Forces in Action – Testing Newton’s Laws With Carts 

Newton’s laws of motion are at the heart of physics, but they really come alive when students can test them in the lab. Using @pascoscientific Smart Carts or simple dynamics trolleys, we can turn abstract principles into measurable results.

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🧑‍🔬 Newton’s First Law – Inertia

A cart at rest stays at rest. A moving cart keeps rolling — until a force (like friction or a barrier) acts on it. Students push, release, and observe how carts continue in motion unless something interferes.

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⚡ Newton’s Second Law – F = ma

With force sensors, motion sensors, or a known hanging weight, students can measure how acceleration changes when they:

• Keep mass constant but vary the pulling force.

• Keep force constant but vary the cart’s mass.

The data plots beautifully onto a straight-line graph, showing that acceleration is directly proportional to force, and inversely proportional to mass.

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💥 Newton’s Third Law – Action and Reaction

When two carts with bumpers collide, the sensors show equal and opposite forces during the impact. It’s one thing to hear “every action has an equal and opposite reaction” — but seeing the mirrored force-time graphs makes it click.

The Effect of Mass on Momentum

Momentum is defined as:

$$p = m \times v$$

Where:

• $p$ is momentum (kg·m/s)

• $m$ is mass (kg)

• $v$ is velocity (m/s)

This means that for the same speed, a heavier object has more momentum than a lighter one.

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🧪 In the Cart Experiment

• Load the cart with extra masses and give it the same push.

• Measure velocity with motion sensors.

• Even if the velocity is similar, the momentum has increased because the mass is greater.

When two carts collide:

• A heavier cart transfers more momentum.

• Students see conservation of momentum in action:

  $$m_1 v_1 + m_2 v_2 = m_1 v_1' + m_2 v_2'$$

This makes the link between Newton’s 2nd Law (F = ma) and momentum crystal clear: a greater mass resists changes in motion but also carries more momentum once moving.

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🎓 Teaching Takeaway

• Mass doesn’t just make things harder to push — it changes the outcome of collisions.

• Students quickly realise why heavy lorries take longer to stop than cars, even at the same speed.

• It’s a perfect bridge between classroom equations and everyday road safety.

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🎓 Why It Works in Teaching

• Students collect real data instead of relying only on theory.

• Graphs reinforce proportionality and the maths behind the laws.

• Collisions and rolling carts add a dose of fun to physics.

Newton’s three laws stop being distant principles and become something students can see, measure, and prove for themselves.