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Momentum

Momentum. What is Momentum?. How do we commonly use the term momentum? Sports!!!! A team that has a lot of momentum is really on the move and is going to be hard to stop . Momentum is a physics term; it refers to the quantity of motion that an object has. . What is Momentum?.

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Momentum

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  1. Momentum

  2. What is Momentum? • How do we commonly use the term momentum? • Sports!!!! • A team that has a lot of momentum is really on the move and is going to be hard to stop. • Momentum is a physics term; it refers to the quantity of motion that an object has.

  3. What is Momentum? • Momentum can be defined as "mass in motion." • The amount of momentum that an object has is dependent upon two variables: • how much stuff is moving • how fast the stuff is moving. Momentum = mass • velocity p = m • v Mo’ Mass Mo’mentum

  4. Momentum and Force • To stop such an object, it is necessary to apply a force againstits motion for a given period of time. • It requires a greater amount of force or a longer amount of time or both to bring such an object to a halt

  5. Momentum and Force • If we take Newton’s 2nd law (F=ma) and combine it with a=Δv/t then we get this: • Multiply both sides by time and you get:

  6. Impulse • In physics, the quantity Force • time is known as impulse. • Since the quantity m•v is the momentum, the quantity m•Δv must be the change in momentum. Impulse = Change in momentum

  7. Impulse-Momentum Theory • In a collision, an object experiences a force for a specific amount of time that results in a change in momentum. • The result of the force acting for the given amount of time is that the object's mass either speeds up or slows down (or changes direction).

  8. If a large truck and a small car hit 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?

  9. Impulse is force multiplied by time, and time of contact is the same for both, so the impulse is the same in magnitude for the two trucks. • Change in momentum is equal to impulse, so changes in momentum are equal. • With equal change in momentum and smaller mass, the change in velocity is larger for the smaller truck. • Since acceleration is change in velocity over change in time, the acceleration is greater for the smaller truck. • RIDE IN THE BIGGER TRUCK!!!

  10. Collisions

  11. Conservation of Momentum • Momentum is conserved in ALL collisions! • Law of conservation of momentum: the momentum of any closed, isolated system does not change • Closed system=a system where mass is neither gained nor lost • Isolated system= there are no forces acting on the system by objects outside of it pf=pi

  12. Kinetic Energy is Energy of motion

  13. Types of Collisions • A perfectly elastic collision is defined as one in which there is no loss of kinetic energy in the collision. • An inelastic collision is one in which part of the kinetic energy is changed to some other form of energy in the collision. • Objects stick together after the collision

  14. Inelastic Collisions • The objects stick togetherafter the collision • This means they share the same velocity after the collision • Only momentum is conserved • m1vi1 + m2vi2 = (m1+ m2)vf

  15. Elastic Collisions • The objects bounce off of each other after the collision • Both momentum and kinetic energy are conserved • m1vi1 + m2vi2 = m1vf1 + m2vf2

  16. Collision Calculations • A 1875 kg car going 23 m/s rear-ends a 1025 kg compact car going 17 m/s on ice in the same direction. The two cars stick together. How fast do the two cars move together immediately after the collisions?

  17. An astronaut at rest in space fires a thruster pistol that expels 35g of hot gas at 875m/s. The combined mass of the astronaut and the pistol is 84kg. How fast and in what direction is the astronaut moving after firing the pistol? • Hint: What unit is mass suppose to be in? • How can you calculate the mass of the astronaut?

  18. A 15 g bullet is shot into a 5.09kg wooden block resting on a frictionless surface. The block, with the bullet in it, acquires a velocity of 1.0m/s. Calculate the velocity of the bullet before striking the block. • Sneak peak of next unit… http://www.youtube.com/watch?v=UQPWdG_ByVY

  19. A tomato, mass of 0.168kg, moving at 25.0 m/s strikes a can sitting on a fence. The can has a mass of 0.523 kg. Calculate the final velocity of the can and tomato if they fly off together.

  20. http://hyperphysics.phy-astr.gsu.edu/hbase/colsta.html#c1

  21. Two-dimensional Collisions • p1i = p1f + p2f • p1i= p1fx +p2fx • p1fy +p2fy = 0 p2f p1i

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