Newton's Third Law
Newton's Third Law is the rule that every push or pull creates an equal push or pull back.
A block sits in the center of a tray. You press down on the block with your palm. The block does not move — it presses back up against your hand with the same force. You can feel the push against your skin. Every push you give the block, the block gives right back.
Explaining newton's third law by grade level
A small boat sits in water with a candle heating a tiny boiler. Steam shoots out the back of the boat. The boat moves forward. The steam pushes back, so the boat gets pushed the other way.
Projects that explore newton's third law
When steam escapes through a small hole in a cork, it pushes backward. That backward push creates an equal forward force that moves the boat. You build a balsa wood boat and mount a sealed metal tube above two candles. As the candles heat the water inside the tube, it turns to steam. The escaping gas pushes the boat forward — the same action-reaction principle that launches real rockets.
When air rushes out of a balloon, it pushes backward. That backward push creates an equal forward push on the car — the escaping air pushes one way, and the car moves the other way. You build a small car from a Styrofoam tray with four pin-and-circle wheels, a flexi-straw, and a balloon taped along the car body. Blow through the straw, set the car on a smooth floor, and let go. A well-built car can travel several meters in a straight line.
Newton's Third Law explains why propeller blades generate thrust: the spinning blade pushes air backward, and the air pushes the vehicle forward with an equal and opposite force. Larger blades move more air per rotation, so the reaction force pushing forward is greater. The largest propeller moved the box in 17 seconds while the smallest took 51 seconds, showing that increasing the backward push on air directly increases the forward push on the vehicle.