Friction
Friction happens when two surfaces rub together. Rough surfaces make more friction; smooth ones make less. Friction is why you can walk — and why brakes work!
Air resistance
Air pushes back against objects moving through it. Parachutes are designed with lots of air resistance to slow you down.
Water resistance
Water pushes back against things moving through it. Boats and fish are streamlined to reduce water resistance.
Upthrust
Water and other liquids push upward on objects in them. This is why some things float!
🔑 Key Terms
- Friction
- A force that resists motion between two surfaces touching.
- Air resistance
- The push of air against a moving object.
- Upthrust
- The upward push of a liquid on an object.
- Streamlined
- Shaped to move easily through air or water.
Did you know?
Sharks have tiny tooth-like scales on their skin that reduce water resistance — engineers copy them to make faster swimsuits!
Try it at home: Float or sink?
- Fill a bowl with water.
- Test 5 small objects (coin, leaf, paperclip, grape, lego).
- Predict first, then test. Why do some float? (Upthrust!)