It would be appropriate to pull out your phone or planner and write these dates down.

Transcription

1 Upcoming dates 11/11 (A) + 11/12 (B): Virtual Collision Lab 11/13 (A) + 11/14 (B): Momentum and Impulse Quiz and Collision Lab 11/17 (A) + 11/18 (B): Momentum and Impulse Vocabulary Quiz and Test Review 11/19 (A) + 11/20 (B): Momentum and Impulse Test 12/8 (A) + 12/9 (B): Egg Drop Project It would be appropriate to pull out your phone or planner and write these dates down.

2 Momentum and Impulse 11/7 (A) 11/10 (B)

3 Quantity Chart Quantity Variable Unit Unit Symbol Momentum p kilogram kg m/s meters per second Mass m kilograms kg Velocity v or v meters per m/s second Impulse J Newton seconds Force F Newtons N Time t or t seconds s N s

4 What is Momentum? The word momentum is used a lot in sports. A team with momentum is on the move and will be hard to stop. A team with a lot of momentum is REALLY on the move and will be REALLY hard to stop. For once, the English language uses it right!

5 Momentum Defined Momentum is mass in motion. Momentum = mass x velocity p = m v Momentum is directly proportional to mass and directly proportional to velocity. m p v p The unit of momentum is kg m/s. Momentum is a vector!

6 Practice Determine the momentum of a... a. 60-kg halfback moving eastward at 9 m/s. b kg car moving northward at 20 m/s. c. 40-kg freshman moving southward at 2 m/s.

7 Impulse How would you stop something with a lot of momentum? You would have to apply a force! Impulse = Force x time J = F t Impulse = change in momentum J = p F t = m v

8 Impulse in real life This idea of impulse is what car companies use when designing air bags. Because the impulse applied to you is going to be equal to your change in momentum, there are two quantities that can be manipulated: force and time. When you increase the amount of time in a collision, the force experienced decreases. Airbags use this idea to lessen the force you feel during a crash. If the time of the collision is shortened, the force experienced increases.

9 Conservation of Momentum Much like energy, momentum is a conserved quantity. When a moving object collides with another object, momentum is conserved.

10 Why do we care if momentum is conserved? Collisions! Elastic Collisions: The moving object stops and all momentum is transferred to the new object. Inelastic Collisions: The moving object sticks to the new object and both keep moving.

11 Momentum and Impulse Momentum is defined as mass in motion. An object with a little momentum is easier to stop than an object with a lot of momentum. You can stop an object with momentum by applying an impulse, that is, a force for a period of time. The impulse applied to an object is equal to the object s change in momentum. In a collision momentum is conserved, which means the momentum before a collision is equal to the momentum after a collision. By Newton s third law, both the of the forces the objects experience during the collision are the same, so the impulse and change in momentum is also the same. The only thing that can be different in a collision is the change in velocity an object experiences.

12 Quantities that are the same A car hits a wall. In the collision, all of the following quantities are the same except: The force of impact on the car and the wall The time of impact of the car and the wall The impulses on the car and the wall The changes in speed/velocity of the car and the wall The changes in momentum of the car and the wall

13 Practice Jennifer, who has a mass of 50.0 kg, is riding at 35.0 m/s in her red sports car when she must suddenly slam on the brakes to avoid hitting a deer crossing the road. She strikes the air bag, that brings her body to a stop in s. What average force does the seat belt exert on her? If Jennifer had not been wearing her seat belt and not had an air bag, then the windshield would have stopped her head in s. What average force would the windshield have exerted on her?

14 A hockey player applies an average force of 80.0 N to a 0.25 kg hockey puck for a time of 0.10 seconds. Determine the impulse experienced by the hockey puck. If a 5-kg object experiences a 10-N force for a duration of 0.10-second, then what is the momentum change of the object?

15 Collision Practice A 60 kilogram astronaut moving at 3 m/s collides with and sticks to his stationary partner of 50 kilograms. What is their new velocity? A 0.5 kilogram ball moving at 1 m/s collides with a 2 kilogram skateboard and comes to a stop. What is the velocity of the skateboard after the collision?

16 Conservation of Momentum Practice A 0.08 kilogram cue ball is moving at 1.7 meters per second when it hits a toy car and comes to a complete stop. If the car has a mass of 0.05 kilogram, what speed is the car moving after the collision? An 55 kilogram ice skater is skating at 4.5 m/s. He swoops down to pick up a 20 kilogram child. After the skater has picked up the child, what speed are they moving at?

17 Impulse-Momentum A force is applied to a 2200 kilogram car initially at rest for 10 seconds. If resulting velocity of the car is 3 m/s, what was the force that was applied?

18 Momentum and Impulse Videos Momentum Cat fight Dance Slow motion explosion Impulse Car and wall Jet and wall Children Conservation Kickback Shotgun

19 Write about it in complete sentences We just watched videos with examples of momentum, impulse and conservation of momentum. Choose to do one of the following: Write about 2 of the examples we just watched, using the vocabulary: momentum, impulse, conservation of momentum, force, time, change in momentum. Write about 1 example from your life, using the vocabulary: momentum, impulse, conservation of momentum, force, time, change in momentum.

20 Notes in brief Momentum: p = m v Impulse: J = F t Impulse-momentum: F t = m v Conservation of momentum: momentum initial ta =momentum final Elastic Collisions: m 1 v 1 =m 2 v 2 Inelastic Collisions: m 1 v 1 =(m 1 +m 2 )v 2