Newton’s Third Law

1. Newton’s Third Law 8th Grade Science Fremont Junior High

2. It’s the Law! Newton’s 3rd Law of Motion states… • For every action, there is an equal and opposite reaction. • So…forces always come in pairs.

3. Applies to objects at rest • An object stands on the floor, pulled down by the force of Earth’s gravity. • However, the object does not move in that direction, because the floor stops it. • The floor is exerting on the object an equal and opposite force. • http://www-istp.gsfc.nasa.gov/stargaze/Snewton3.htm

4. Applies to Objects in Motion • The oars move in a backwards motion • The boat moves forward. • The movement of the oar is the “action.” • The movement of the boat is the “reaction.” • The movements are opposite in direction but equal in force. Boat Oars

5. Applies to Objects in Motion • The swimmers arms move in a backwards motion • The swimmer moves forward. • The movement of the arm is the “action.” • The movement of the swimmer’s body is the “reaction.” • The movements are opposite in direction but equal in force. swimmer arm motion

6. Applies to Objects in Motion • The hot gases move in a downward motion • The rocket moves upward. • The movement of the gases is the “action.” • The movement of the rocket is the “reaction.” • The movements are opposite in direction but equal in force. Rocket hot gases

7. Applies to Objects in motion + objects at rest • The toe exerts a force on the rock. • The rock exerts a force on the toe. • The movement of the foot is the “action.” • The force of the rock is the “reaction.” • The movements are opposite in direction but equal in force. • The greater the force, the greater the impact (pain)

8. Applies to Objects in motion + objects at rest • The runner exerts a force on the starting block. • The starting block exerts a force on the runner. • The push of the foot against the starting block is the “action.” • The force of the starting block is the “reaction.” • The forces are opposite in direction but equal in force. • The greater the force, the greater “push off”

9. Skateboarding • The foot exerts a force against the ground. • The ground exerts a force on the foot. • The push of the foot is the “action.” • The force of the ground is the “reaction.” • The forces are opposite in direction but equal in force. • The greater the force, the faster the rider will go.

10. Rifle Recoil • A gunpowder explosion creates hot gases that expand outward allowing the rifle to push forward on the bullet. • The bullet pushes backwards upon the rifle. The acceleration of the recoiling rifle is ... • a. greater than the acceleration of the bullet. • b. smaller than the acceleration of the bullet. • c. the same size as the acceleration of the bullet.