Newton's Third Law of Motion — Examples
For every action, there is an equal and opposite reaction. When you push something, it pushes you back with the same force. This applies everywhere — from walking on the ground to launching rockets into space.
Newton's third law states: when object A exerts a force on object B, object B simultaneously exerts a force of equal magnitude but opposite direction on object A. These are called action-reaction pairs. They always act on different objects, which is why they don't cancel each other out.
10 Real-World Examples
🚶 1. Walking
Your foot pushes the ground backward. The ground pushes your foot forward. That reaction force propels you.
🚀 2. Rocket Launch
The rocket expels exhaust gas downward at high speed. The gas pushes the rocket upward. No air needed — works in space!
🏊 3. Swimming
Your hands push water backward. The water pushes your body forward.
🍏 4. Apple Falling (Gravity)
Earth pulls the apple down with gravity. The apple pulls Earth up with the same force! Earth doesn't visibly move because its mass is enormous.
💺 5. Sitting in a Chair
Your body pushes down on the chair (your weight). The chair pushes up on you (normal force).
🚗 6. Car Collision
Car A hits Car B with 50,000 N of force. Car B hits Car A with exactly 50,000 N. The smaller car sustains more damage because it has less mass and therefore greater acceleration (F = ma).
💺 7. Pushing a Wall
You push the wall with 100 N. The wall pushes you back with 100 N. Neither moves because both forces are balanced by friction and structure.
🎾 8. Hitting a Ball
A bat hits a ball with 5,000 N of force for 1 ms. The ball hits the bat with the same 5,000 N. The ball accelerates more because it has far less mass.
🚢 9. Rowing a Boat
The oar pushes water backward. The water pushes the oar (and boat) forward.
🌞 10. Earth Orbiting the Sun
The Sun pulls Earth inward (gravity). Earth pulls the Sun outward with the same force. The Sun wobbles slightly — this is how astronomers detect exoplanets!
The #1 Misconception
"If forces are equal and opposite, how does anything move?"
This is the most common confusion. The answer: action and reaction forces act on different objects. When you push a shopping cart, your force acts on the cart (making it accelerate). The cart's reaction force acts on you (pushing you backward slightly). The cart moves because the only horizontal force on it is your push — the reaction force is on you, not the cart.
When you jump, your feet push Earth downward and Earth pushes you upward. You accelerate dramatically; Earth accelerates by about 10−²³ m/s² — trillions of times too small to measure.
People Also Ask
Does Newton's third law apply in space?
Absolutely. Rockets work precisely because of Newton's third law — they push exhaust gas backward and the gas pushes them forward. No air or ground is needed. All spacecraft manoeuvres rely on action-reaction.
What is the difference between Newton's three laws?
1st law: An object stays at rest or constant velocity unless a net force acts (inertia). 2nd law: F = ma (quantifies the acceleration). 3rd law: Every force has an equal and opposite reaction force (force pairs).
Are weight and normal force a Newton's third law pair?
No! Your weight (Earth pulling you down) and the normal force (floor pushing you up) act on the same object (you). The true third-law pair for your weight is: Earth pulls you down, and you pull Earth up.
References and further reading
- Taylor, J. R. Classical Mechanics. University Science Books, 2005.
- Goldstein, H., Poole, C. & Safko, J. Classical Mechanics, 3rd ed. Addison-Wesley, 2002.