Unit B, Chapter 4,Lesson 5

Action and Reaction

• Newton’s third law states that when one object exerts a force on another object, the second object exerts an equal force and moves in the opposite direction.– Example: A frog jumping off a Lilly pad.

• All forces come in pairs.– They are called action and reaction forces.– If you push down on your desk, or lean against a

wall, the desk and the wall push against you with an equal force.

• Forces must be balanced whenever an object is at rest.

Action and Reaction

• People who design rockets use Newton’s Third Law.

- For example, the gases that are in a rocket’s engine push backward and makes the rocket go up.

• When you walk it is also an example of action and reaction.

– When you push your foot on the ground the ground pushes back with equal force.

– Since you push your foot off the ground, it makes you move forward.

Newton’s Laws at the Amusement Park

• Motion, gravity, mass, forces, acceleration, friction, inertia, and reaction, are all important parts of amusement park rides.– An example of the first law is a roller coaster

and the swings. • If you didn’t have straps on a roller coaster you

would fall out and get seriously injured. • When the swings start moving in a circular

motion, you would fly out of your seat. It wouldn’t be pleasant!

Newton’s Laws at the Amusement Park

– Another example of the second law is hitting a target with enough force to make the bell ring. It tests your strength.

– An example of a ride using Newton’s third law is bumper cars. When they hit, they bounce backward with an equal force.

– Newton’s law can be displayed in all different rides. Next time your on a ride, think about what law might be demonstrated.