1 / 23

What is Momentum?

What is Momentum?. An object with a lot of momentum is also hard to stop Momentum = p = mv Units: kg ∙m/s m=mass v=velocity Momentum is also a vector (it has direction). How hard is it to stop a moving object?. To stop an object, a force must be applied for a period of time.

hagen
Download Presentation

What is Momentum?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. What is Momentum? An object with a lot of momentum is also hard to stop Momentum = p = mv Units: kg∙m/s m=mass v=velocity Momentum is also a vector (it has direction)

  2. How hard is it to stop a moving object? To stop an object, a force must be applied for a period of time. This is called Impulse Impulse = FΔt Units: N∙s F = force (N) Δt = time elapsed (s)

  3. How hard is it to stop a moving object? • Using Newton’s 2nd Law we get FΔt= mΔv Which means Impulse = change in momentum

  4. Why does an egg break or not break? • An egg dropped on a tile floor breaks, but an egg dropped on a pillow does not. Why? FΔt= mΔv In both cases, m and Δv are the same. If Δt goes up, what happens to F, the force? Right! Force decreases. When dropped on a pillow, the egg starts to slow down as soon as it touches it. A pillow increases the time needed to stop the egg.

  5. A Thought Experiment: • Suppose that you were captured by an evil physicist who gave you the following choice: • You must either: • Stand in front of a 1000 kg. truck moving at 1 m/s, or • Stand in front of a 1 kg. frozen meatball moving at 1000 m/s. • …think…

  6. Truck: • Truck's momentum = mv = (1000 kg)(1 m/s) = 1000 kg m/s • Truck's kinetic energy = 0.5 mv2 = (0.5)(1000 kg)(1 m/s)2 = 500 Joules • Meatball: • Meatball's momentum = mv = (1 kg)(1000 m/s) = 1000 kg m/s • Meatball's kinetic energy = 0.5 mv2 = (0.5)(1kg) (1000 m/s)2 = 500 000 Joules

  7. Diagramming: • A 120 kg lineman moving west at 2 m/s tackles an 80 kg football fullback moving east at 8 m/s. After the collision, both players move east at 2 m/s. Draw a vector diagram in which the before- and after-collision momenta of each player is represented by a momentum vector. Label the magnitude of each momentum vector.

  8. Answer to previous slide question www.physicsclassroom.com

  9. impulse = change in momentum • www.physicsclassroom.com

  10. Bouncing increases impulse explain... • www.physicsclassroom.com

  11. Impulse= change in momentum • www.physicsclassroom.com

  12. Elastic collisions: momentum is redistributed or transferred without loss. m1v1o+ m2v2o= m1 v1f +m2v2f

  13. Inelastic collisions: when two objects become entangled m1v1o+ m2v2o= (m1+m2)vf

  14. M M M M Inelastic Collisions v = 10 v = 0 Before Collision p = mv v’ = 5 After Collision p = 2mv’ mv = 2mv v’ = ½ v

  15. Granny & Little Timmy: calculate the final velocity. • www.physicsclassroom.com

  16. Law of Conservation of Momentum • In the absence of an external force, the momentum of a system does not change. • www.physicsclassroom.com

  17. Truck Collision • In a head-on collision: • Which truck will experience the greatest force? • Which truck will experience the greatest impulse? • Which truck will experience the greatest change in momentum? • Which truck will experience the greatest change in velocity? • Which truck will experience the greatest acceleration? • Which truck would you rather be in during the collision? http://hyperphysics.phy-astr.gsu.edu/hbase/truckc.html#c1

  18. http://hyperphysics.phy-astr.gsu.edu/hbase/truckc.html#c2 Ride in the BIG truck! 

  19. Stopping a Truck • Suppose a large truck and a small truck are moving with equal momentum. Which will require more work to stop? Which will require more force to stop in a given distance? http://hyperphysics.phy-astr.gsu.edu/hbase/truckc2.html#c1

  20. More Force to Stop the Little Truck!?? • Since the little truck is moving substantially faster it will have more Kinetic Energy!

  21. Impulse http://sol.sci.uop.edu/~jfalward/physics17/chapter3/chapter3.html

  22. YIKES! • If the boulder and the boyhave the same momentum,will the boulder crush the boy? • …do not try this at home! http://sol.sci.uop.edu/~jfalward/physics17/chapter3/chapter3.html

  23. Two Dimensional Collision • The purple ball which is twice as massive as the green ball, is initially moving at 5 m/s. After the collision the purple ball moves at 3 m/s at 20º North of East. What is the velocity of the green ball after the collision? http://turing.kingsu.ca/~map/java/applets/collisions_2D/applethelp/lesson/fig01a.png

More Related