Friction in air and water

The idea

Air, water and other liquids also exert a force of friction on objects moving through them.

Moving through water

A boat moves through water. An aeroplane moves through air.

Do air and water exert friction on a moving object?

• Yes, both do
• Only solid surfaces do
• Neither does

Air or water

Pick air, then water. Press Move the ball in each.

Friction everywhere

Both air and water pushed back on the ball, against its motion. So aeroplanes, ships, boats and high-speed trains are designed with special shapes to reduce this friction.

Air, water and other liquids also exert a force of friction on objects moving through them. Aeroplanes, ships, boats and high-speed trains have specific shapes to reduce it.

Notes

Air, water and other liquids also exert a force of friction on objects moving through them. Specific shapes reduce it.

Check yourself

Which of these exerts friction on a moving boat?

An aeroplane moves through the air. The air …

Why do aeroplanes and high-speed trains have specific shapes?

Does friction act only on objects moving over solid surfaces?

• The water — correct. Yes!
• Nothing, boats are free. Water and other liquids exert friction on objects moving through them.
• Only the sky. The water around the boat exerts friction on it.
• exerts no force on it. Air also exerts friction on objects moving through it.
• exerts a force of friction on it — correct. Yes!
• pulls it with a magnet. The force from the air is friction.
• To make friction larger. They are designed to reduce friction.
• Only to look nice. The shapes are designed to reduce the friction of the air.
• To reduce the force of friction from the air — correct. Yes!
• No, liquids and gases also exert friction — correct. Yes!
• Yes, only solids. Air, water and other liquids also exert friction.
• Yes, only on the ground. Objects moving through air or water also feel friction.