Newton’s Third Law Section 10.4 Standard 2: Forces Students know a force has both ____________ and ____________. Students know when an object is subject to two or more forces at once, the result is a ______________. Students know when the forces on an object are balanced, the motion of the object ________________. Students know how to identify separately the two or more forces that are acting on a single static object, including __________, _________ due to tension or compression in matter, and __________. Students know that when the forces on an object are unbalanced, the object will ________________. Students know the ____________ the mass of an object, the _______ force is needed to achieve the same rate of change in motion.

Warm Up! 1. The amount of force required to start a 6-kg object accelerating at 2 m/s/s is: 2. A flying squirrel is moving at a constant velocity of 18 m/s. What is the amount of force required to keep it moving? (Are the forces balanced or unbalanced?) 3. Which objects could be moving to the right? Try to use the length of the arrow as the strength of the force.

Recap Newton’s First 2 Laws An object in motion will stay in motion and an object at rest will stay at rest until acted upon by a force Newton’s Second Law: Force = Mass x Acceleration F = ma

Newton’s Third Law What is the law? If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction What does that mean? For every ACTION. . . there is an equal and opposite REACTION Example: Rocket! Coke and Mentos Rocket http://youtu.be/OLbjrio5GWo ACTION (Gases push downward) REACTION (Rocket pushes upward)

Action/Reaction Pairs

What is the action? Reaction?

What is the action? Reaction?

What is the action? Reaction?

State the action and reaction.

Think about it! So if the force is equal and opposite, it cancels out the other force, right? But, what about Newton’s 1st Law? It takes an unbalanced force to change motion. So how does the man push the car? How does the gun shoot a bullet? How does the rocket launch?

Two Different Objects! When the gymnast does a flip, she pushes down on the vaulting horse (action force). The reaction force of the vaulting horse pushes her up to complete the flip.

What is momentum. How much motion something has What is momentum? How much motion something has! Depending upon both mass and velocity How do we calculate momentum? Momentum = Mass x Velocity Momentum is a vector quantity What does that mean? Momentum

Conservation of Momentum “Momentum is Conserved” In the absence of outside forces, the total momentum of objects that interact does not change. (What does that sound like?) A turtle is on the ice rink with a heavy medicine ball. If he throws the ball forward, what happens to him?

Conservation of Momentum Case #1: Two Objects are moving and energy is transferred!

Conservation of Momentum Case #2: One Object is moving and transfers ALL its energy!

Conservation of Momentum Case #3: One object sticks to another and slows down