Building an A Level Platform Game Project — Part 4: Adding Platforms and Collision Detection

In Part 1, we planned the platform game and set realistic success criteria.

In Part 2, we created the game window and added basic left and right movement.

In Part 3, we added gravity and jumping, so the player could rise, fall and land on the ground.

Now we reach one of the most important stages in the whole project: platforms and collision detection.

This is where the game stops being a character jumping on a single ground line and starts to become a proper platform game world.

It is also where many students discover that game programming is not quite as simple as it first appears.

A platform looks simple. It is just a rectangle on the screen.

But the program has to answer some awkward questions:

• Has the player landed on top of the platform?

• Has the player hit the side of the platform?

• Has the player jumped into the underside of the platform?

• Should the player stand on the platform or fall through it?

• What happens if the player is moving quickly?

• How does the program know which platform the player is touching?

This is why collision detection is such a good A Level Computer Science topic. It takes a simple visual idea and turns it into a proper programming problem.

Why Platforms Matter

A platform game needs a world for the player to interact with.

So far, our player can move, jump and land, but only on the bottom of the screen. That is useful for testing, but it is not enough for a game.

Platforms allow us to create:

• different routes through the level

• jumps of different difficulty

• collectables placed in interesting positions

• hazards that must be avoided

• areas that require planning and timing

• a proper start and finish point

Once platforms work, we can begin to design levels.

That is why this article is so important. Collision detection is the bridge between movement and level design.

The Aim for Part 4

The aim of this stage is:

Add rectangular platforms to the game and allow the player to land on them without falling through.

By the end of this stage, the game should include:

• several visible platforms

• a player affected by gravity

• collision detection between the player and platforms

• the ability to land on top of platforms

• prevention of repeated jumping while in the air

• testing evidence showing that platforms work correctly

This is still a prototype, but it is now much closer to a real game.

Representing Platforms

The simplest platform can be represented as a rectangle.

In Pygame-style code, a platform might be written as:

platform = pygame.Rect(200, 450, 200, 20)

This creates a rectangle with:

• x-position: 200

• y-position: 450

• width: 200

• height: 20

Instead of one platform, we can store several platforms in a list:

platforms = [
    pygame.Rect(0, 580, 800, 20),
    pygame.Rect(150, 480, 200, 20),
    pygame.Rect(450, 380, 200, 20),
    pygame.Rect(250, 280, 180, 20)
]

This gives us a basic level layout:

• a ground platform at the bottom

• one platform slightly higher

• another platform further across

• a higher platform above

This simple list is already important.

It means the level is not just drawn manually. It is stored as data.

That is a key idea for future articles, because later we can develop this into proper level design.

Drawing the Platforms

Once the platforms are stored in a list, they can be drawn using a loop:

for platform in platforms:
    pygame.draw.rect(screen, (0, 0, 0), platform)

This is better than writing a separate drawing command for every platform.

It also makes the project easier to extend.

If we want to add another platform, we add another rectangle to the list. The drawing loop does not need to change.

This is a good point for students to mention in their project documentation:

I stored the platforms in a list so that the program could process them using a loop. This made it easier to add, remove or change platforms without rewriting the drawing code.

That shows good programming thinking.

Representing the Player as a Rectangle

In earlier versions, the player used separate variables such as:

player_x
player_y
player_width
player_height

For collision detection, it is useful to create a rectangle for the player as well:

player_rect = pygame.Rect(player_x, player_y, player_width, player_height)

A rectangle makes it easier to check whether the player overlaps a platform.

For example:

if player_rect.colliderect(platform):
    print("Collision detected")

This is the basic idea behind rectangle collision detection.

It is not perfect, but it is ideal for a first platform game.

What Is Collision Detection?

Collision detection means checking whether two objects are touching or overlapping.

In this project, we need to know when the player touches:

• the ground

• a platform

• a wall

• a hazard

• a collectable

• a finish point

For now, we will focus only on platforms.

The simplest approach is rectangle collision detection.

If the player rectangle overlaps a platform rectangle, a collision has happened.

That sounds easy.

The difficult part is deciding what to do after the collision.

Why Collision Response Is Harder Than Collision Detection

Detecting a collision simply tells us that two rectangles overlap.

It does not automatically tell us where the collision happened.

The player might have:

• landed on top of the platform

• hit the platform from below

• run into the side

• touched a corner

The response should be different in each case.

If the player lands on top, they should stand on the platform.

If the player hits the underside, they should stop moving upwards.

If the player hits the side, they should not pass through the platform.

For this stage, we will keep things simple and focus on landing on top of platforms.

Side collisions can be developed later.

This is a sensible project decision because it controls the scope.

A Simple Landing Algorithm

To land on a platform, the program needs to check whether the player is falling and whether the bottom of the player has reached the top of the platform.

The player is falling when:

player_y_velocity > 0

The bottom of the player is:

player_rect.bottom

The top of the platform is:

platform.top

If the player is falling and collides with a platform, we can place the player on top of the platform:

player_rect.bottom = platform.top
player_y_velocity = 0
on_ground = True

This means:

• the player is no longer falling

• the player is positioned exactly on top of the platform

• the player is allowed to jump again

That is the basic idea.

Updating the Player Position

One important issue is that the player’s rectangle must be updated as the player moves.

A sensible structure is:

1. Check input.

2. Move horizontally.

3. Apply gravity.

4. Move vertically.

5. Check collisions with platforms.

6. Draw everything.

The order matters.

If the order is wrong, collisions may behave strangely.

For example, if the program checks collisions before the player moves, it may be using old position data.

Example Code for Platforms and Landing

Here is a simplified version of the Part 4 prototype:

import pygame

pygame.init()

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600

screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))
pygame.display.set_caption("Escape the Platforms")

clock = pygame.time.Clock()

player_rect = pygame.Rect(100, 500, 40, 60)
player_speed = 5
player_y_velocity = 0

gravity = 0.5
jump_strength = -12
on_ground = False

platforms = [
    pygame.Rect(0, 580, 800, 20),
    pygame.Rect(150, 480, 200, 20),
    pygame.Rect(450, 380, 200, 20),
    pygame.Rect(250, 280, 180, 20)
]

running = True

while running:
    clock.tick(60)

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    keys = pygame.key.get_pressed()

    # Horizontal movement
    if keys[pygame.K_LEFT]:
        player_rect.x -= player_speed

    if keys[pygame.K_RIGHT]:
        player_rect.x += player_speed

    # Screen boundary checks
    if player_rect.left < 0:
        player_rect.left = 0

    if player_rect.right > SCREEN_WIDTH:
        player_rect.right = SCREEN_WIDTH

    # Jumping
    if keys[pygame.K_SPACE] and on_ground:
        player_y_velocity = jump_strength
        on_ground = False

    # Apply gravity
    player_y_velocity += gravity
    player_rect.y += player_y_velocity

    # Assume the player is not on the ground until a platform proves otherwise
    on_ground = False

    # Platform collision detection
    for platform in platforms:
        if player_rect.colliderect(platform) and player_y_velocity > 0:
            player_rect.bottom = platform.top
            player_y_velocity = 0
            on_ground = True

    # Draw everything
    screen.fill((255, 255, 255))

    for platform in platforms:
        pygame.draw.rect(screen, (0, 0, 0), platform)

    pygame.draw.rect(screen, (0, 0, 255), player_rect)

    pygame.display.update()

pygame.quit()

This is a major step forward.

The player now interacts with platforms.

The player can jump, fall and land on different surfaces.

The level is still basic, but it is becoming a real platform game.

Why on_ground = False Is Reset Each Frame

This line is important:

on_ground = False

It appears before checking platform collisions.

At first, this may look strange.

Why set on_ground to False when the player might be on a platform?

The reason is that each frame, the program should check the current situation again.

The player is assumed to be in the air unless a collision with a platform proves they are standing on something.

If the player is touching a platform from above, the collision code sets:

on_ground = True

This keeps the jumping logic accurate.

Without this, the game might incorrectly think the player is still on the ground after walking off the edge of a platform.

That is an excellent bug to discuss in the project write-up.

The Walk-Off-the-Platform Problem

One of the most important tests is what happens when the player walks off a platform.

The expected result is simple:

The player should fall.

However, if the on_ground variable is not updated correctly, the player may be able to jump in mid-air after walking off the edge.

That would be a bug.

The solution is to reset on_ground each frame and only set it to True when a platform collision confirms that the player is standing on something.

This is a good example of state management.

The program must keep track of whether the player is grounded, but that state must be checked and updated continuously.

Common Collision Detection Bugs

This stage is likely to produce bugs. That is not a failure. It is exactly why this makes a good A Level project.

Bug 1: The Player Falls Through Platforms

This can happen if the player is moving too fast or if the collision check is in the wrong place.

Possible fixes include:

• checking collisions after vertical movement

• reducing gravity

• limiting the maximum falling speed

• checking whether the player was above the platform in the previous frame

Bug 2: The Player Gets Stuck Inside a Platform

This often happens when the player overlaps a platform but is not moved back to a safe position.

A simple fix is:

player_rect.bottom = platform.top

This places the player exactly on top of the platform.

Bug 3: The Player Can Jump After Walking Off a Platform

This usually happens because on_ground remains True after the player leaves the platform.

Resetting on_ground each frame helps solve this.

Bug 4: The Player Lands on the Side of a Platform

If the collision detection is too simple, the game may treat a side collision as a landing.

This is one reason why more advanced collision detection often separates horizontal and vertical movement.

For now, we are focusing mainly on landing from above. Later, students may improve the algorithm to handle side collisions more accurately.

Separating Horizontal and Vertical Collision

A more advanced approach is to deal with horizontal and vertical movement separately.

The program can:

1. Move the player horizontally.

2. Check for side collisions.

3. Move the player vertically.

4. Check for floor or ceiling collisions.

This is more complex, but it gives better control.

For example, if the player moves horizontally into a wall, the program can stop sideways movement without affecting vertical movement.

If the player falls onto a platform, the program can stop vertical movement without affecting horizontal movement.

This is something students could add as an extension once the basic version works.

It would also make a strong discussion point in the evaluation.

Using Platform Data for Future Levels

At the moment, our platforms are stored like this:

platforms = [
    pygame.Rect(0, 580, 800, 20),
    pygame.Rect(150, 480, 200, 20),
    pygame.Rect(450, 380, 200, 20),
    pygame.Rect(250, 280, 180, 20)
]

This is already a simple form of level design.

If we change the numbers, we change the level.

For example, moving a platform higher makes the jump harder.
Making a platform narrower makes landing more difficult.
Placing platforms further apart changes the route.
Adding a platform creates a new possible path.

This is where students can begin to see the connection between code and game design.

The level is not just decoration. It is data.

In the next part of the series, we can develop this further by creating proper levels, perhaps storing them as lists, dictionaries or external files.

Designing a First Test Level

A good first test level should not be too difficult.

The aim is to test the mechanics, not frustrate the player.

A sensible first level might include:

• a wide ground platform

• one low platform that is easy to jump onto

• a second platform slightly higher

• a third platform further away

• a finish point that will be added later

For now, the goal is simply to check that the player can land on each platform.

Students should avoid making the platforms too small too early.

Difficult levels should come after reliable mechanics.

Testing Platforms and Collision Detection

Testing is essential at this stage.

Students should create a test table that checks normal movement and awkward cases.

Test Number	Test	Expected Result	Actual Result	Pass/Fail
1	Run the program	Player appears and platforms are visible	Player and platforms appear	Pass
2	Player falls onto ground platform	Player lands and stops falling	Player lands correctly	Pass
3	Jump onto first raised platform	Player lands on top of platform	Player lands correctly	Pass
4	Walk off a raised platform	Player falls downwards	Player falls correctly	Pass
5	Press jump while standing on platform	Player jumps upwards	Player jumps correctly	Pass
6	Press jump after walking off platform	Player should not jump again in mid-air	Player cannot jump in mid-air	Pass
7	Land on second platform	Player lands and can jump again	Player lands correctly	Pass
8	Hit side of platform	Player should not behave unpredictably	Needs improvement	Fail/Partial
9	Fall from top platform to ground	Player lands on lower surface	Player lands correctly	Pass
10	Move to screen edge	Player remains inside screen	Player remains inside screen	Pass

Notice that one test may not fully pass.

That is acceptable if it is recorded honestly.

A project that identifies limitations and suggests improvements is often stronger than one that pretends everything is perfect.

Linking Back to Success Criteria

This stage supports several success criteria from the planning article:

• The game contains several platforms.

• The player can stand on the top of each platform.

• The player falls when not standing on a platform.

• The player can jump from a platform.

• The player cannot repeatedly jump while in the air.

• The player can move left and right while jumping.

• The player remains within the screen boundaries.

Students should keep referring back to the original criteria.

This makes the project feel coherent rather than random.

A good development log entry might say:

This stage met the success criteria relating to platforms, jumping and landing. The player can now land on several rectangular platforms. Testing showed that walking off a platform causes the player to fall, which fixed an earlier problem where the player could still jump after leaving the platform.

That is strong project evidence.

Evidence Students Should Collect

For this stage, useful evidence might include:

• screenshot of the platform layout

• screenshot of the player standing on a platform

• screenshot of the player falling between platforms

• code showing the platform list

• code showing collision detection

• test table for landing and falling

• notes about bugs and fixes

• short video showing the player jumping between platforms

The most important thing is to collect evidence while the work is happening.

Trying to recreate evidence at the end of the project is much harder.

Personal Reflection: This Is Where Students Start to Understand Games Differently

This is one of my favourite stages when teaching programming projects.

At the beginning, students often think of games mainly in terms of graphics.

They talk about characters, backgrounds and visual style.

But when they add platforms and collision detection, they begin to see that a game is really a system of rules.

A platform is not just a rectangle.

It is something the player can stand on, fall from, jump from and interact with.

The program has to decide what touching means.

That is a powerful lesson.

Students begin to understand that programming is not simply making something appear on screen. It is defining behaviour.

That is why a simple retro platform game can be such a good project.

It looks small, but it contains real computational thinking.

Practical Task for Students

Before moving on to level design, students should complete this task.

Part 4 Student Task

Add platforms and collision detection to your platform game.

Your program should include:

1. At least four platforms, including the ground.

2. Platforms stored in a list.

3. A loop to draw all platforms.

4. A player rectangle used for collision detection.

5. Gravity applied each frame.

6. Collision detection between the player and platforms.

7. A landing response that places the player on top of the platform.

8. An on_ground variable that updates correctly.

9. A test table for platform collisions.

10. Screenshots or video evidence of the player landing on platforms.

Extension Task

Improve the platform system by adding one of the following:

• side collision detection

• ceiling collision detection

• moving platforms

• one-way platforms

• different platform types

• platforms stored in a separate level data structure

• a simple finish point

• a debug mode showing collision rectangles

Students should only attempt extensions once the basic collision detection is reliable.

Development Log Example

A good development log entry might look like this:

Development Stage

Adding platforms and collision detection.

Aim

To allow the player to land on raised platforms instead of only landing on the bottom of the screen.

What Was Added

• platform list

• platform drawing loop

• player rectangle for collision detection

• collision detection using rectangle overlap

• landing response when falling onto a platform

• updated on_ground logic

Problems Found

• The player could initially jump after walking off a platform.

• The player sometimes overlapped slightly with a platform before being corrected.

• Side collisions were not handled accurately in the first version.

Changes Made

• Reset on_ground to False each frame.

• Set on_ground to True only when landing on a platform.

• Set the bottom of the player rectangle to the top of the platform after collision.

• Recorded side collision as an area for later improvement.

Evidence Collected

• screenshots of the player on platforms

• code showing the platform list

• code showing collision detection

• test table

• notes explaining the walk-off-platform bug

This sort of development record is exactly what students need for a strong A Level project.

Preparing for Levels

Once platforms work, we are ready for the next major step: level design.

A level is more than a random collection of platforms.

A good level has:

• a start point

• a route

• increasing challenge

• safe areas

• risk areas

• a finish point

• opportunities for scoring

• suitable difficulty for the target user

At the moment, our platforms are hard-coded into one list.

That is fine for the prototype.

But as the game grows, we can improve this by storing levels as separate data structures.

For example, we might eventually have:

level_1_platforms = [...]
level_2_platforms = [...]
level_3_platforms = [...]

Or we might store level data in dictionaries:

level_1 = {
    "platforms": [...],
    "player_start": (100, 500),
    "finish": (700, 520)
}

This opens the door to multiple levels.

It also creates excellent A Level project material because the student can explain how the game data is organised.

Final Thoughts: Collision Detection Turns Movement Into a Game

Adding platforms and collision detection is a major step in the project.

The player is no longer just moving around a blank screen.

The player is now interacting with a world.

They can jump onto platforms, fall from them, land on them and begin to move through a level.

This stage also creates some of the best learning moments in the whole project. The bugs are real. The problems are interesting. The solutions require thought.

The player may fall through platforms.
They may get stuck.
They may jump when they should not.
They may collide from the side in unexpected ways.

All of that is valuable.

A good A Level project is not one where everything works perfectly first time. It is one where the student can show how they found problems, tested them, improved the program and explained the decisions they made.

With platforms now working, the project is ready to move from mechanics to design.

In the next article, we will look at how to turn these platforms into proper levels, with routes, difficulty, start points, finish points, collectables and hazards.

 

Making Something Useful from Chemistry: Building a Lead–Acid Accumulator

Chemistry lessons often involve colour changes, precipitates, gases and equations. These can be interesting, but students sometimes leave the laboratory wondering what any of it is actually for.

Making a simple lead–acid accumulator changes that.

Using two carefully prepared lead sheets, dilute sulfuric acid, beakers, connecting wires and a low-voltage power supply, it is possible to construct a device that stores electrical energy chemically. After charging it for only a few minutes, the accumulator can be disconnected from the supply and used to light a small bulb.

For a student, that moment is important.

The bulb may not be especially bright and it may not stay illuminated for very long, but the electricity is no longer coming directly from the power supply. Energy has been stored inside the chemicals and then released again.

That is chemistry doing something useful.

A Battery Built in the Laboratory

The basic apparatus looks surprisingly simple:

• two lead sheets;

• dilute sulfuric acid;

• a beaker;

• connecting wires;

• a low-voltage direct-current supply;

• an ammeter and voltmeter;

• a small bulb or suitable low-voltage load.

The lead sheets first need careful preparation. Grease, dirt and surface contamination can prevent good contact between the metal and the electrolyte. In our experiment, the sheets were degreased and soaked in sodium hydroxide solution for approximately 10 minutes before being rinsed and placed in the sulfuric acid.

This preparation is not merely tidying the apparatus. It is part of the science.

Electrochemical reactions happen at the surfaces of the electrodes. A contaminated surface can reduce the effective area available for reaction, increase the internal resistance and make the results much less reliable.

The Royal Society of Chemistry describes a comparable classroom experiment using lead strips and dilute sulfuric acid to demonstrate the operation of a rechargeable lead–acid accumulator.

An Important Correction: An Accumulator Is a Rechargeable Battery

It is easy to describe the investigation as exploring why accumulators are used in cars rather than rechargeable batteries. However, a lead–acid accumulator is a rechargeable battery.

The useful comparison is between a lead–acid accumulator and other rechargeable technologies, such as:

• lithium-ion batteries;

• nickel-metal hydride batteries;

• rechargeable alkaline systems;

• newer solid-state or sodium-ion technologies.

The word accumulator emphasises that the device accumulates or stores electrical energy. In modern everyday language, we are more likely to call it a rechargeable battery.

A single lead–acid cell produces a voltage of roughly two volts. A conventional 12-volt car battery contains six such cells connected in series.

Our beaker cell was therefore not intended to reproduce the full performance of a car battery. It was a model that allowed us to investigate the same underlying chemistry.

What Happens During Charging?

Initially, both electrodes are lead. When the cell is connected to a direct-current supply, electrical energy forces chemical changes to take place at their surfaces.

The electrode connected to the positive terminal gradually develops a coating containing lead dioxide, PbO₂. The negative electrode remains largely as lead, although its surface becomes more active and porous.

The charging process is an example of electrolysis. A non-spontaneous chemical change is being driven by an external source of electricity.

This is one of the most useful links students can make between different parts of chemistry. Electrolysis is not simply about producing copper at an electrode or splitting a molten ionic compound. It can also be used to place a chemical system into a higher-energy state.

The electrical supply does not disappear into the cell. Its energy is stored through chemical changes in the electrodes and electrolyte.

What Happens During Discharge?

After charging, the power supply is removed and the cell is connected to a bulb.

The chemical reactions now proceed in the opposite direction. Electrons flow through the external circuit from the negative electrode, through the bulb and towards the positive electrode.

At the negative electrode, lead reacts with sulfate ions:

Pb + SO₄²⁻ → PbSO₄ + 2e⁻

At the positive electrode, lead dioxide reacts with hydrogen ions, sulfate ions and electrons:

PbO₂ + 4H⁺ + SO₄²⁻ + 2e⁻ → PbSO₄ + 2H₂O

The overall discharge reaction is:

Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O

Both electrodes gradually become coated with lead sulfate. At the same time, sulfuric acid is consumed and water is formed.

The stored chemical energy is converted back into electrical energy, which is then transferred by the bulb into light and thermal energy.

The Moment the Bulb Lights

There is something particularly satisfying about disconnecting the charging supply, attaching the bulb and seeing it light.

Before that moment, the experiment can appear to be little more than two grey pieces of metal sitting in a colourless liquid. There is no dramatic flame, vivid colour or obvious movement.

Then the bulb glows.

It provides visible evidence that something has changed inside the cell.

This is why practical chemistry matters. A diagram of a lead–acid cell can show the electrodes and equations, but it cannot reproduce the experience of making one work.

The glow of the bulb creates questions:

• Where did the energy come from?

• Why does the bulb gradually become dimmer?

• Why does the terminal voltage fall?

• Can the cell be recharged?

• How much of the original energy is recovered?

• What limits its performance?

These questions turn a demonstration into a genuine scientific investigation.

Measuring the Charging Energy

To calculate the efficiency of the accumulator, we first need to estimate how much electrical energy is supplied during charging.

Electrical energy is calculated using:

Energy = potential difference × current × time

or:

E = VIt

where:

• E is energy in joules;

• V is potential difference in volts;

• I is current in amperes;

• t is time in seconds.

Suppose the accumulator is charged at:

• 3.0 V;

• 0.40 A;

• for 300 seconds.

The charging energy would be:

E = 3.0 × 0.40 × 300

E = 360 J

This assumes that the voltage and current remain approximately constant. For a more accurate investigation, readings should be taken at regular intervals and the energy calculated from the area beneath a power–time graph.

Because:

Power = voltage × current

we can plot power against time. The area beneath that graph represents the electrical energy supplied.

Measuring the Energy Recovered

The charged accumulator is then connected to the bulb or another suitable resistor.

The output energy can again be estimated using:

E = VIt

Suppose the bulb operates with an average potential difference of 1.7 V and an average current of 0.15 A for 240 seconds.

The recovered electrical energy would be:

E = 1.7 × 0.15 × 240

E = 61.2 J

The energy efficiency would then be:

Efficiency = useful energy output ÷ total energy input × 100

Efficiency = 61.2 ÷ 360 × 100

Efficiency = 17%

A simple classroom cell may have quite a low efficiency. That does not mean the experiment has failed. It gives us something more interesting to investigate.

Where Does the Missing Energy Go?

Energy is conserved, but not all of the charging energy can be recovered as useful electrical energy.

Some is transferred through:

• heating of the electrolyte;

• heating of the wires and electrodes;

• electrical resistance inside the cell;

• unwanted gas production;

• incomplete or competing chemical reactions;

• energy remaining chemically stored when the test is stopped;

• losses caused by contamination or poor electrode contact.

The bulb itself also converts only part of its electrical input into visible light. Much of the energy becomes thermal energy.

This creates an important distinction.

If we are calculating the electrical efficiency of the accumulator, the useful output is the electrical energy delivered to the bulb.

If we are calculating the efficiency of the complete system as a source of visible light, we would also need to consider the efficiency of the bulb.

That is a much more difficult measurement.

Making the Investigation More Scientific

A single successful demonstration proves that the accumulator can store energy. A proper investigation asks what affects its performance.

Students could investigate:

Charging time

Does doubling the charging time double the energy recovered?

At first, a longer charging period may increase the discharge time. Eventually, however, further charging may produce diminishing returns or encourage unwanted reactions.

Electrode surface area

Larger electrodes provide more surface area for electrochemical reactions. This may reduce internal resistance and allow a larger current to flow.

Distance between the electrodes

Moving the electrodes further apart increases the distance ions must travel through the electrolyte. This can increase resistance and reduce the current.

The electrodes must not touch, as this would short-circuit the cell.

Condition of the lead surfaces

Clean, roughened or porous surfaces may behave differently from smooth or contaminated surfaces.

This makes the lengthy preparation of the lead sheets scientifically significant rather than merely procedural.

Discharge current

A small load may allow the accumulator to operate for longer, while a low-resistance load may draw a larger current but discharge the cell rapidly.

Number of cells

Cells can be connected in series to increase the voltage. They can also be connected in parallel to increase current capacity, although this requires cells with closely matched characteristics.

Voltage Is Not the Same as Stored Energy

Students sometimes measure the terminal voltage and assume that the cell with the highest voltage stores the most energy.

That is not necessarily true.

A cell can produce a measurable voltage but be unable to maintain that voltage when a significant current is drawn. Its internal resistance may be high, or only a small quantity of reactant may be available.

A useful battery must provide both:

• an appropriate voltage;

• sufficient current for a useful length of time.

This is why measuring only the open-circuit voltage gives an incomplete picture.

The accumulator should also be tested under load. Measuring voltage and current while the bulb is operating reveals much more about its actual performance.

Why Lead–Acid Batteries Are Used in Cars

A petrol or diesel engine needs a substantial burst of electrical power to operate its starter motor. Turning the engine requires a very large current for a relatively short time.

Lead–acid batteries are well suited to this job because they can be designed to provide high power, are relatively inexpensive and have a long-established reputation for reliability. Their disadvantages include low energy per unit mass and a shorter cycle life than some newer chemistries.

This is the central point.

A traditional car battery does not need to provide moderate power for hundreds of kilometres. Its main job is to supply a brief but powerful starting current and then support the vehicle’s electrical systems. Once the engine is running, the alternator recharges it.

Lead–acid batteries are also used for stop–start systems and for ancillary electrical loads in some electric vehicles. The main traction batteries in modern electric vehicles are usually lithium-ion because lithium-ion cells store considerably more energy for their mass and volume.

Why Not Use Lithium-Ion for Every Car Battery?

Lithium-ion batteries are lighter and have much greater energy density. That makes them ideal when weight and stored energy are critical, especially in electric vehicles, phones and laptops.

However, a vehicle’s low-voltage battery has different requirements.

It must be:

• dependable;

• capable of delivering high current;

• tolerant of repeated charging;

• economical to replace;

• compatible with established vehicle charging systems;

• supported by a reliable recycling network.

Lead–acid technology is mature, widely available and comparatively inexpensive. Replacing it is not simply a question of finding a battery that stores more energy. The replacement must satisfy the whole engineering specification.

This is an excellent example of why engineers rarely ask, “Which material is best?”

They ask, “Which material is best for this particular job?”

The Environmental Question

Lead is toxic, and sulfuric acid is corrosive. A lead–acid battery should never be treated as ordinary rubbish.

The technology remains viable partly because collection and recycling systems are already well established. The US Environmental Protection Agency reports a 99% recycling rate for lead–acid batteries in its cited national data and describes a collection network involving retailers, manufacturers and specialist recyclers.

High recycling rates do not make lead harmless. They demonstrate the importance of designing a complete system around a hazardous but useful material.

The environmental judgement therefore cannot be based only on what happens while the battery is inside the car. It must include:

• extraction of raw materials;

• manufacturing;

• working life;

• maintenance;

• collection;

• recycling;

• safe handling of lead and acid;

• prevention of contamination.

This wider life-cycle thinking is increasingly important across science and engineering.

Safety Must Come First

This is not a casual home experiment.

Sulfuric acid is corrosive, sodium hydroxide is corrosive, lead is toxic, and charging can produce gases if the conditions are not properly controlled. The activity should only be carried out in a suitably equipped laboratory under competent supervision, using an approved risk assessment and appropriate local guidance.

Essential precautions include:

• suitable eye protection and protective clothing;

• careful control of acid and alkali concentrations;

• good ventilation;

• avoiding flames and ignition sources;

• using a current-limited low-voltage supply;

• preventing the electrodes from touching;

• washing hands thoroughly after handling lead;

• collecting all lead-containing materials and solutions as hazardous waste;

• never pouring lead-contaminated liquids down a sink.

The purpose of the experiment is to teach electrochemistry, not to reproduce a commercial battery without industrial safeguards.

From a Beaker to a Car

The laboratory accumulator is small, inefficient and temporary. A car battery is sealed, carefully engineered and constructed with many plates to provide a very large effective surface area.

Yet both depend on the same principles:

• oxidation and reduction;

• movement of electrons through an external circuit;

• movement of ions through an electrolyte;

• reversible chemical reactions;

• conversion between electrical and chemical energy.

That connection is what makes the investigation so valuable.

Students are not simply memorising half-equations. They are seeing how those equations describe a working energy-storage device.

Chemistry That Earns Its Place

I find experiments like this particularly valuable because they answer a question students often do not ask aloud:

Why are we learning this?

We learn about ions because their movement allows charge to be transported through an electrolyte.

We learn about oxidation states because electrons are transferred during charging and discharging.

We learn about electrolysis because electrical energy can drive chemical change.

We learn about energy calculations because a working device must be measured, compared and improved.

We learn about efficiency because no real system returns all the energy supplied to it in a useful form.

Most importantly, we learn that chemistry is not confined to bottles on a laboratory shelf. It is inside vehicles, phones, emergency power systems, renewable-energy installations and almost every modern electrical device.

Conclusion: When the Chemistry Becomes Real

Two pieces of prepared lead, a beaker of sulfuric acid and some wires do not initially look like an energy-storage system.

After a few minutes of charging, however, they can light a bulb.

That small glow represents a remarkable sequence of energy transfers. Electrical energy has driven chemical reactions, the products have stored energy, and the reverse reactions have released electrical energy into a circuit.

The accumulator may not be especially efficient. Its voltage may fall rapidly and its light may be brief. Those limitations are not reasons to dismiss it. They are opportunities to measure, explain and improve it.

The experiment brings together redox chemistry, electrolysis, electrical circuits, energy, power, efficiency, materials science and environmental responsibility.

Above all, it shows students that chemistry can make something genuinely useful.

Sometimes the best way to understand a battery is not merely to draw one.

It is to build one, charge it and watch the bulb come on.

 

The Hidden Frequencies Inside Everything: Understanding Resonance

Why can a small, repeated force sometimes produce an enormous vibration?

It seems counter-intuitive. We normally expect a small force to have a small effect and a large force to have a large effect. Yet a child can make a playground swing rise higher and higher using a series of relatively gentle pushes. A singer can occasionally make an object vibrate noticeably. A musical instrument can turn the faint vibration of a string into a sound that fills a room.

The explanation is resonance.

Resonance is often mentioned briefly in physics courses, perhaps as a definition to be remembered for an examination. However, it is far more important than a single line in a specification. Resonance helps us understand musical instruments, buildings, bridges, machinery, radio receivers, microwave ovens and medical imaging.

It also reveals something fascinating about the physical world:

Every object has frequencies at which it naturally prefers to vibrate.

Everything Can Vibrate

We tend to think of vibration as something associated with obvious objects such as guitar strings, tuning forks and loudspeakers. In reality, almost every physical object can vibrate.

A ruler hanging over the edge of a desk can move up and down.

A wine glass can vibrate around its rim.

A bridge can bend and twist.

The air inside a tube can oscillate.

The body of a guitar can flex.

Even atoms and molecules can vibrate.

The exact way in which an object vibrates depends on factors including:

• its mass;

• its shape;

• its stiffness;

• its dimensions;

• the material from which it is made;

• how it is supported or fixed.

These properties determine the object’s natural frequencies.

A natural frequency is a frequency at which an object can vibrate particularly easily after it has been disturbed. Strike a tuning fork and it vibrates at its natural frequency. Pull a pendulum to one side and release it, and it swings at a frequency determined mainly by its length.

Many objects do not have just one natural frequency. They have several possible patterns of vibration, known as modes.

From Natural Frequency to Resonance

A vibrating system can be made to oscillate by applying an external force. This is called a driving force.

The driving force may be:

• a person pushing a swing;

• a motor causing a machine to vibrate;

• moving air acting on a bridge;

• a loudspeaker producing changing air pressure;

• an alternating electrical signal in a circuit.

When the frequency of the driving force is close to one of the system’s natural frequencies, energy is transferred particularly efficiently.

The amplitude of the vibration increases.

This is resonance.

A useful definition is:

Resonance occurs when a system is driven at or near one of its natural frequencies, producing a large-amplitude oscillation.

The force does not necessarily need to be large. What matters is its timing.

The Playground Swing: Resonance in Its Simplest Form

A playground swing is one of the clearest everyday examples.

Imagine pushing the swing at random moments. Some pushes help it to move, while others oppose its motion. Very little energy is transferred efficiently.

Now apply a small push every time the swing reaches the correct point in its motion. Each push adds a little more energy. The amplitude gradually increases, and the swing rises higher.

The individual pushes may be small, but their effects accumulate because they are applied at the correct frequency and phase.

This is why resonance is not simply about repeating a force. The force must be repeated at the right time.

A poorly timed force can reduce a vibration just as easily as a well-timed force can increase it.

Standing Waves: Patterns That Appear Not to Move

Resonance is closely connected with standing waves.

A standing wave forms when two waves of the same frequency travel in opposite directions and overlap. This often occurs when a wave reflects from the end or boundary of a system.

The two waves interfere with one another, creating a fixed pattern.

Some points remain almost stationary. These are called nodes.

Other points vibrate with the greatest amplitude. These are called antinodes.

Standing waves are sometimes misunderstood because of their name. The material is not completely still, and energy has not stopped existing. Instead, the pattern of nodes and antinodes remains in a fixed position.

Strings, air columns, plates and electromagnetic fields can all form standing-wave patterns.

Revealing Hidden Patterns with a Chladni Plate

One of the most visually impressive resonance demonstrations uses a Chladni plate.

A thin metal plate is supported, and a small amount of salt or fine sand is scattered across its surface. The plate is then made to vibrate using a bow or a mechanical vibration generator.

At most frequencies, the grains move around without forming a clear pattern.

At certain frequencies, however, something remarkable happens. The grains jump away from the parts of the plate that are vibrating strongly and collect along the lines that are moving very little.

These lines are nodes.

The resulting geometric patterns reveal the standing waves across the plate.

Changing the frequency produces a different vibration mode and therefore a different pattern.

This demonstration makes an otherwise invisible idea visible. Students are not merely being told that nodes exist. They can see their positions mapped out by the grains.

I find that this is often the moment when resonance stops being an abstract definition and becomes something real. The plate may appear simple, but it contains many possible patterns of movement. Each pattern has its own frequency.

The hidden frequencies were present all along. The experiment simply reveals them.

Tuning Forks and Sympathetic Vibration

Tuning forks provide another useful demonstration.

Strike one tuning fork and it produces a nearly pure musical note. The frequency depends on the dimensions and material of the fork.

Place two tuning forks of the same frequency close together. Strike the first fork, allow it to vibrate and then stop it with your hand. The second fork may continue producing a sound even though it was never struck directly.

Sound waves from the first fork have driven the second fork at its natural frequency.

This is sometimes called sympathetic vibration.

Repeat the experiment using two tuning forks with noticeably different frequencies and the effect is much weaker. The second fork does not respond strongly because the driving frequency does not match its natural frequency.

This comparison is valuable because it demonstrates that resonance is selective. An object does not respond equally to every frequency.

Coupled Pendulums: Matching Lengths Matter

Pendulums provide a simple way to explore the same idea at a much lower frequency.

Several pendulums can be suspended from a shared support. Some should have the same length, while others should have different lengths.

Set one pendulum swinging.

The movement creates small vibrations in the shared support. These vibrations act as a driving force on the other pendulums.

The pendulum with the matching length begins to oscillate more noticeably because it has approximately the same natural frequency. Pendulums with different lengths respond much less strongly.

This is a particularly useful demonstration because the movement is slow enough to observe carefully.

Students can see that energy is being transferred from one oscillator to another. They can also watch the amplitude of the first pendulum decrease as the matching pendulum begins moving.

It is resonance, but it also introduces the wider idea of coupled oscillators: systems that can exchange energy through a connection between them.

Resonance in Air Columns

Sound is produced by vibrations travelling through a medium, usually air.

The air inside a pipe or tube can also resonate.

A useful practical investigation involves a signal generator connected to a loudspeaker placed near the end of a tube. The frequency is varied gradually while the sound level is monitored.

At particular frequencies, the sound becomes noticeably louder.

These are resonant frequencies of the air column.

Depending on whether the ends of the tube are open or closed, different standing-wave patterns are possible. Nodes and antinodes form at particular positions along the air column.

This principle is central to wind instruments.

A flute, clarinet, recorder, organ pipe or brass instrument does not simply produce sound because air is blown through it. The air column inside the instrument resonates. Changing the effective length of that air column changes the natural frequencies and therefore changes the notes produced.

Opening and closing holes, pressing valves or moving a slide alters the available resonant modes.

Music is therefore closely connected with standing waves.

Why a Guitar String Needs a Guitar Body

Stretch a guitar string between two rigid supports and pluck it. The string vibrates, but on its own it moves very little air. The sound is surprisingly quiet.

Attach the string to the body of a guitar and the result is completely different.

The vibrating string transfers energy through the bridge into the larger wooden soundboard and body. These components vibrate and move a much greater volume of air.

The hollow body also contains resonant air modes that contribute to the instrument’s sound.

The instrument is not simply making the string louder. Its materials, dimensions and resonant frequencies influence the character or timbre of the note.

This is why two instruments playing the same note can sound different.

Instrument makers are therefore managing resonance. They select materials, shapes, thicknesses and internal structures that produce a desirable response across a range of frequencies.

Resonance Can Be Useful or Dangerous

Resonance is neither inherently good nor bad.

In musical instruments, it is essential.

In machinery or structures, it may be destructive.

Engineers must decide whether to encourage resonance, control it or avoid it entirely.

Bridges and Buildings

Bridges and buildings have natural frequencies just as strings and tuning forks do.

Wind, footsteps, traffic and machinery can apply repeated forces. When a driving frequency is close to a structural natural frequency, oscillations may grow.

Modern engineering therefore includes careful analysis of vibration modes.

Designers can:

• change the stiffness of a structure;

• alter its mass;

• add damping;

• install tuned mass dampers;

• change the shape to reduce aerodynamic forces;

• ensure regular driving forces do not match important natural frequencies.

A tuned mass damper is a large moving mass installed within a structure. It is designed to move in a way that counteracts unwanted motion, reducing the vibration experienced by the main building or bridge.

This is resonance being controlled by another carefully designed oscillator.

Suspension Systems and Vehicles

A car’s suspension system contains springs and dampers.

The springs allow the wheels to move over uneven surfaces, but a spring alone would cause the car to continue bouncing.

The dampers remove energy from the oscillation and reduce its amplitude.

Suspension designers must consider the natural frequency of the vehicle and the repeated forces produced by the road. Poor damping could make a vehicle uncomfortable, unstable or difficult to control.

The same general principles apply to trains, bicycles and aircraft.

Machinery and Unwanted Vibration

Rotating machinery can produce repeated forces because of imbalance, misalignment or worn components.

If the rotation frequency approaches a natural frequency of the machine or its supporting structure, the vibration can become much larger.

This may result in:

• excessive noise;

• inaccurate operation;

• loosening fasteners;

• damaged bearings;

• metal fatigue;

• eventual mechanical failure.

Engineers can measure the vibration spectrum of a machine to identify unusually strong frequencies. This can help detect faults before serious damage occurs.

A vibration is not merely an inconvenience. It can contain information about the condition of the machine producing it.

Radio Tuning and Electrical Resonance

Resonance is not limited to mechanical movement.

Electrical circuits containing inductance and capacitance can also have natural frequencies.

In a radio receiver, a tuning circuit can be adjusted so that its resonant frequency matches the frequency of the desired radio signal. That signal produces a stronger response than signals at other frequencies.

Turning the tuning control changes the resonant frequency of the circuit.

The radio can therefore select one station from the many electromagnetic waves arriving at its aerial.

The same fundamental idea appears again: a system responds most strongly when the driving frequency matches its natural frequency.

Standing Waves in a Microwave Oven

A microwave oven contains electromagnetic waves that reflect from its metal walls.

The reflected waves interfere, producing standing-wave patterns inside the oven cavity. Some regions have stronger electromagnetic fields than others, contributing to uneven heating.

This helps explain why food may develop hot and cold regions.

A rotating turntable moves the food through different parts of the standing-wave pattern, helping to average out the heating.

A simple demonstration can be performed only under appropriate supervision by removing the turntable rotation and observing the spacing of melted regions in a suitable food. However, microwave experiments require careful risk assessment, and the oven must never be operated incorrectly or with inappropriate objects inside it.

The important physics is that standing waves are not restricted to ropes, strings or sound. Electromagnetic waves can form them too.

Resonance in Medical Imaging

Magnetic resonance imaging, or MRI, uses a form of resonance involving atomic nuclei.

In a strong magnetic field, certain nuclei can respond to radio-frequency energy. By applying carefully controlled signals and detecting the resulting response, the equipment can build detailed images of structures inside the body.

The physics is far more advanced than a classroom pendulum or tuning fork, but the broad principle is related: a system responds strongly to energy supplied at an appropriate frequency.

A simple classroom idea can therefore develop into one of the most important tools in modern medical diagnosis.

The Importance of Damping

In real systems, vibrations do not usually continue forever.

Energy is transferred to the surroundings through:

• friction;

• air resistance;

• internal deformation;

• electrical resistance;

• sound;

• heating.

This loss of energy is called damping.

Damping limits the amplitude of resonance.

With very little damping, the resonant response can be sharp and large. A small change in frequency can produce a dramatic change in amplitude.

With greater damping, the maximum amplitude is lower and the response is spread across a wider range of frequencies.

This creates an important engineering trade-off.

A musical instrument may need sufficient resonance to produce a rich, sustained sound. A vehicle suspension or tall building may require enough damping to prevent uncomfortable or dangerous movement.

A Practical Resonance Lesson

A useful lesson could be organised as a sequence of connected demonstrations:

1. Begin with a pendulum or swing

Establish that correctly timed pushes increase the amplitude.

2. Compare tuning forks

Show that matching frequencies produce a much stronger response than non-matching frequencies.

3. Use coupled pendulums

Allow students to see energy transfer between systems with similar natural frequencies.

4. Reveal standing waves on a Chladni plate

Make nodes and vibration modes visible.

5. Investigate a resonant air column

Use a signal generator and loudspeaker to locate resonant frequencies.

6. Examine a musical instrument

Compare the quiet sound of an isolated string with the amplified sound created when the body resonates.

Students can then identify the same physics appearing in several different forms.

The apparatus changes, but the central pattern remains:

A system has natural frequencies. A repeated force supplies energy. When the frequencies match, the response becomes much larger.

What Students Often Miss

Students can sometimes repeat the definition of resonance without understanding the mechanism.

The most important ideas are:

• the driving force does not need to be large;

• timing is more important than the size of each individual push;

• resonance involves efficient energy transfer;

• the forcing frequency must be close to a natural frequency;

• standing waves contain nodes and antinodes;

• real systems lose energy through damping;

• one object may have several natural frequencies and vibration modes.

Once these points are understood, resonance becomes much more than an examination term.

It becomes a way of interpreting the behaviour of the world.

The Hidden Frequencies Around Us

A tuning fork, guitar, bridge, building and radio receiver appear to be very different systems.

Yet all can be understood using the same underlying principles.

Each has characteristics that determine how it naturally responds.

Each can be driven by an external influence.

Each responds particularly strongly at certain frequencies.

That is one of the most satisfying parts of physics. A concept first demonstrated with a pendulum or a vibrating metal plate can explain musical notes, mechanical failures, communication systems and medical technology.

Resonance reminds us that a small action can have a large effect when it is applied in the right way, at the right time and at the right frequency.

The world is full of hidden patterns of vibration.

We simply need the right experiment to reveal them.