1. Newton’s Third Law of Motion Building Science Champions

2. In thought http://www.wimp.com/spaceshuttle/ After watching the Discovery launch, explain how Newton’s three laws are used by NASA scientist to launch a space shuttle.

3. Objectives State Newton’s third law of motion Define and calculate momentum and state the law of conservation of momentum

4. Key Terms Force pair Momentum Law of conservation of momentum Elastic collision Inelastic collision

5. Newton’s Third Law of Motion Newton realized forces are not one direction One object exerts a force on the second; while the second exerts a force back on the first Second’s force is equal to and opposite of the first First force is action and the second force is reaction IF ONE OBJECT EXERTS A FORCE ON ANOTHER OBJECT, THEN THE SECOND OBJECT EXERTS A FORCE OF EQUAL STRENGTH IN THE OPPOSITE DIRECTION ON THE FIRST OBJECT IMPORTANT

6. Force Pairs Forces in Newton’s 3 rd law depend on each other Force pair – is the force two objects apply to each other Why don’t equal but opposite forces cancel each other out? Because each force acts on a different object The person is pushing on the diving board The diving board is pushing on the person 2 separate forces

7. Equal but Opposite Action Force Reaction Force EqualEqual Opposite When contact between the two players is made the forces are equal. The players flying backwards is the opposite force. The ground is the unbalanced force that will stop the players fall. The force the white player hits the blue player with is transferred to the blue player and that is equal to the force that he will fall with.

8. Action-Reaction in Action A squid brings water in, then expels it to move Action expulsion of water Reaction Squid moves forward A space shuttle burns fuel to create thrust, a pushing force, the ground pushes back on the shuttle Reaction Action

9. Momentum Momentum (p) – is the product of an object’s mass and it’s velocity p = mv Mass is measures in kilograms (kg) and velocity is measured in meters per second (m/s) Momentum is also described by it’s direction as well as its quantity

10. Momentum Problem Which has more momentum: a 3-kg sledgehammer swung at 1.5 m/s or an 4-kg sledgehammer swung at 0.9 m/s? Momentum = mass x velocity 3 kg x 1.5 m/s = 4.5 kg x m/s 4 kg x 0.9 m/s = 3.6 kg x m/s

11. Practice Problems Golf ball = 0.72 kg x m/s baseball = 0.98 kg x m/s A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has greater momentum? What is the momentum of a bird with a mass of 0.018 kg flying at 15 m/s? Bird = 0.27 kg x m/s

12. Conservation of Momentum Law of conservation of momentum – the total momentum of the objects that interact does not change Quantity of momentum is the same before and after they interact Total momentum of any group of objects remains the same unless outside forces act on the objects Conservation refers to conditions before and after an event A quantity that is conserved is the same after an event as it was before the event

13. Types of Collisions Objects collide with one another in two different ways Elastic collision – when colliding objects bounce off one another in the collision Inelastic collision – when colliding objects stick to another No matter the type of collision, the total momentum will be the same before and after the collision

14. Two Moving Objects Look at the two trains traveling in the same direction, train 1 is traveling at 10 kmph and train 2 is traveling at 5 kmph 10 km p h 5 km p h When the trains collide the speed of each car changes Train 2 is now traveling at 10 kmph and train 1 is now traveling at 5 kmph 10 km p h 5 km p h Momentum is conserved – the momentum of one train decreases while the momentum of the other increases

15. One Moving Object Cue ball is moving toward the stationary billiard balls Stationary MovingMoving The momentum from the cue ball is transferred to all the other billiard balls Cue ball will become stationary, the stationary billiard balls will go in motion Stationary Momentum The momentum is the same before and after the collision. This time the momentum from the cue ball is transferred to numerous other billiard balls.

16. Two Connected Objects Instead of objects bouncing off of each (elastic collision) other sometimes they will remain connected (inelastic collision) Player A is running at 4 m/s and player B is stationary 4 m/s Stationary Once contact is made, the two players will share the momentum of player A 2 m/s 2 m /s The momentum of the two players is still conserved

17. Review Momentum’s formula is p=mv Elastic collisions the objects bounce off one another Inelastic collisions the objects stay connected Reactions are opposite but equal to the action Newton’s third law is action/reaction

18. References Anderson, M. et all (2012) Physical Science. McGraw- Hill: Columbus Frank, D.V et al (2001). Physical Science. Prentice Hall: New Jersey