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## Momentum

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**Momentum**Chapter 7**Momentum**“Inertia in Motion” mass X velocity mv**Momentum**mass X velocity mv If traveling at the same speed, which has more momentum?**Momentum**What if they had the same momentum? mv = mv**What is the momentum of a 0.50 kg kitten running with a**velocity of 1.00 m/s to the left?**What is the momentum of a 0.50 kg kitten running with a**velocity of 1.00 m/s to the left? Given: Substitute: m = 0.50 kg p = (0.50 kg)(1.00 m/s) v = 1.00 m/s Unknown: Solve: p (momentum) p = 0.5 kgm/s Equation: p = mv**Jenny has a mass of 35.6 kg and her skateboard has a mass of**1.3 kg. What is the momentum of Jenny and her skateboard together if they are going 9.50 m/s?**Jenny has a mass of 35.6 kg and her skateboard has a mass of**1.3 kg. What is the momentum of Jenny and her skateboard together if they are going 9.50 m/s? Given: Equation: m = 36.9 kg p=mv v = 9.50 m/s Substitute: Unknown: p = (36.9 kg)(9.50 m/s) p (momentum) Solve: p = 350.55 kgm/s**How do we change momentum?**• Change in mass • example: items falling out of a truck • Change in velocity**What is the term for change in velocity?**• Acceleration And what causes acceleration? FORCES!**Impulse**• Any change in momentum, but usually occurs as a change in speed What besides force would cause a change in momentum? TIME! Ft**Impulse**v = 20 m/s v = 20 m/s Which would you rather hit?**Impulse**Ft And you look like:**Impulse**Ft And you look like:**While being thrown, a net force of 132 N acts on a baseball**(mass = 140 g) for a period of 4.5 X 10-2 sec. What is the magnitude of the change in momentum of the ball?**When the batter hits the ball, a net force of 1320 N,**opposite to the direction of the ball’s initial motion, acts on the ball for 9.0 X 10-3 s during the hit. What is the change in momentum of the ball? What force does the ball exert on the bat in the question above?**A 1.00 kg ball traveling at a velocity of 3.00 m/s west**strikes a wall and rebounds with a velocity of 3.00 m/s east. The ball contracts the wall for 0.01 s. • What is the ball’s momentum before it hits the wall?**A 1.00 kg ball traveling at a velocity of 3.00 m/s west**strikes a wall and rebounds with a velocity of 3.00 m/s east. The ball contracts the wall for 0.01 s. • What is the ball’s momentum before it hits the wall? -3 kgm/s • What is the ball’s momentum after it hits the wall?**A 1.00 kg ball traveling at a velocity of 3.00 m/s west**strikes a wall and rebounds with a velocity of 3.00 m/s east. The ball contracts the wall for 0.01 s. • What is the ball’s momentum before it hits the wall? -3 kgm/s • What is the ball’s momentum after it hits the wall? 3 kgm/s • What is the ball’s change in momentum?**A 1.00 kg ball traveling at a velocity of 3.00 m/s west**strikes a wall and rebounds with a velocity of 3.00 m/s east. The ball contracts the wall for 0.01 s. • What is the ball’s momentum before it hits the wall? -3 kgm/s • What is the ball’s momentum after it hits the wall? 3 kgm/s • What is the ball’s change in momentum? 6 Ns • What force must the wall exert on the ball in order to change its momentum?**Bouncing**Requires more impulse than stopping.**Bouncing**The flat paddle just stops the water.**Bouncing**The curved paddle causes the water to make a U-turn or bounce.**Impulse Question**On a sheet of paper, answer the following question, using what was discussed yesterday about impulse and momentum. Which would you rather hit and why? or**Conservation of Momentum**-mv = mv Before firing:After firing: momentum = 0 momentum = 0 0 + 0 = 0 mV + (-Mv) = 0**Conservation of Momentum**• Law of Conservation of Momentum: In the absence of an external force, the momentum of a system remains unchanged. • If no external forces are applied to the system, momentum is conserved.**Elastic collisions**Momentum is conserved The total momentum for the system does not change Energy is also conserved Collisions**Elastic collisions**Basically, if A and B have the same masses, they simply swap velocities after the collision. Collisions**Inelastic collisions**Momentum is still conserved, but energy is lost due to an outside force (like friction) Usually occurs when there is a change in mass or when the two masses combine to form one object. Collisions**If the objects have the same mass.**With elastic collisions, starting and ending velocities are equal. With inelastic collisions, starting velocities are reduced Collisions