Air Resistance and Drag

The invisible push of the air

You cannot see air. It feels like there is nothing around you at all. But the next time you stick your hand out of a car window (carefully, with a grown-up driving slowly), you will feel something pushing your hand backward. That push is air resistance. It is a real force, even though the air is invisible.

Scientists also call air resistance drag. Drag is the way the air pushes back against anything that tries to move through it. The faster you move, the more you can feel it. Run as fast as you can and you will feel the air rushing against your face — that is drag pushing on you.

Where does the push come from?

Air is made of tiny bits called particles, far too small to see. When you move forward, you bump into millions and millions of these air particles. They get in your way and push back at you. The more particles you have to push out of the way, the bigger the drag force.

This is why air resistance does two important things:

• It gets bigger when you go faster, because you bump into the air particles more quickly.
• It gets bigger when you have a larger surface facing the air, because a bigger front bumps into more particles at once.

A famous test: the feather and the paper

Hold up a flat sheet of paper and a small coin. Drop them at the same time. The coin lands first, and the paper flutters slowly down. Why? It is not because the coin is "better" at falling. It is because the wide, flat paper catches a lot of air, so drag pushes up on it and slows it down. The small coin slips through the air easily.

Now scrunch that same sheet of paper into a tight ball and drop it again. This time it falls much faster — almost as fast as the coin! The paper still weighs exactly the same, but now it is small and has much less surface to catch the air. With less drag, it drops quickly. This little test proves that shape and size, not just weight, decide how much air resistance pushes back.

Streamlined shapes slip through

Some shapes are good at cutting through the air. We call them streamlined. A streamlined shape is smooth and pointed at the front, so the air slides around it instead of crashing into it.

Think about the things that move fast through air:

• A bird folds its wings and points its beak forward when it dives.
• A racing car is low and smooth so the air flows over it.
• An aeroplane has a pointed nose and sleek wings. To learn more about how planes use the air, see the physics of flight.
• An arrow has a sharp tip and slim body so it flies straight and fast.

A flat board held face-on is the opposite of streamlined. It pushes against a huge wall of air, so it has lots of drag and slows down quickly.

Using drag on purpose: the parachute

Sometimes we want lots of air resistance. A parachute is a brilliant example. When a parachute opens, it spreads out into a huge dome shape. That enormous surface catches a massive amount of air, so the drag force becomes very strong — strong enough to slow a falling person down to a safe, gentle speed for landing.

Without the parachute, the person would fall fast because the pull of gravity speeds them up. With the parachute open, the big push of the air balances the pull of gravity, and the fall becomes slow and steady. Nature uses the same trick: a dandelion seed has a fluffy little parachute so the wind can carry it far away.

Why air resistance matters

Air resistance is happening all around you, all the time. It is why a kite stays up, why a feather floats down, why fast cars are shaped the way they are, and why a parachute keeps a skydiver safe. Once you know that the air can push back, you start to notice it everywhere — in the breeze on a bike, the flutter of a flag, and the slow drift of a falling leaf.

Try it yourself! 🧪

The paper drop race — totally safe and a bit surprising.

1. Take two sheets of paper that are exactly the same size and weight.
2. Leave one sheet flat. Scrunch the other one up into a tight little ball.
3. Hold both up at the same height, level with each other. Let go of both at the same moment.
4. Watch carefully. Which one lands first?

The scrunched ball wins the race almost every time! Both pieces of paper weigh the same, so this proves it is the shape that matters. The flat sheet catches lots of air (more drag, slower fall); the little ball catches very little air (less drag, faster fall).

Bonus: make a tiny parachute. Tie four equal pieces of thread to the corners of a square of a plastic bag, then tie the other ends to a small toy or a cork. Drop it from a safe, low height (like standing on the bottom step, with a grown-up nearby) and watch how the big plastic dome catches the air and floats the toy down gently.