Why Do We Float? Exploring Archimedes in the Swimming Pool

 Physics is everywhere — even in your holiday paddling pool. Buoyancy, anyone?

Why Do We Float? Exploring Archimedes in the Swimming Pool

It’s summer. The students are on holiday, the lab is a bit quieter… and yet physics is still very much at work – especially if you’ve taken to the pool for a well-earned dip. Whether you’re bobbing gently on a lilo or sinking like a brick after a cannonball, you’re living proof that Archimedes’ Principle is alive and kicking.

💡 The Eureka Moment (In a Bath)

Archimedes of Syracuse was reportedly taking a bath when he noticed that the water rose as he got in. According to legend, this observation sparked such excitement that he ran through the streets naked shouting, “Eureka!” (I have found it!).

What he found was the principle that explains why things float:

Archimedes' Principle: An object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces.

Put simply: when you’re in the pool, the water pushes back.

🏖️ Why Some Things Float (and Others Don’t)

Let’s test this with your beach bag:

• Inflatable beach ball? Floats brilliantly. It displaces lots of water but weighs very little. The upward force is greater than its weight.

• Swim goggles? Sink. Small volume, not much water displaced, so not enough upward force to keep them afloat.

• You? Surprisingly floaty—thanks to the air in your lungs and the fat in your body (yes, it helps).

Even humans can float, provided the buoyant force exceeds their body weight. Try lying on your back and holding a full breath – you’ll find yourself bobbing gently at the surface.

⚖️ The Physics of Floating

The balance of forces is everything:

• Downwards force = weight (mass × gravity)

• Upwards force = buoyant force (equal to the weight of water displaced)

If upward > downward, you float.
If downward > upward, you sink.

That's why heavier objects with small volume sink, and why ships (very heavy but very wide) float.

🧪 Try This Experiment (Pool Optional)

If you have access to a pool – great! If not, a washing-up bowl and a few objects will do.

You’ll need:

• Bowl of water

• Orange (whole)

• Orange (peeled)

• Spoon

• Stone

• Plastic cup (with and without holes)

What to do:

1. Predict which objects will float.

2. Place each gently in the water.

3. Observe what happens and relate it to how much water each displaces.

4. Try sinking the cup – and then fill it with air bubbles underwater. What happens?

Bonus observation: A peeled orange sinks, but a whole one floats. That’s because the peel traps air and increases volume without adding much weight.

🏗️ Archimedes in Engineering

It’s not just poolside trivia. Archimedes’ principle is essential for:

• Boat design

• Submarine operation

• Hydraulic lifts

• Measuring density via water displacement

It’s a principle we build ships on – quite literally.

🎯 Why It Matters

Teaching students about buoyancy through real-life examples – especially ones they’re already experiencing over the summer – reinforces the idea that physics isn’t just in the textbook. It’s in the pool, the bath, the sea, and your fizzy drink can bobbing in the ice bucket.

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Interested in hands-on physics?
At Philip M Russell Ltd, we teach A-Level and GCSE Physics in our lab, online studio, or one-to-one in person. Whether you want to float or fly, we’ll help you grasp the science behind it.

📅 Book your place for September: www.philipmrussell.co.uk