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MOMENTUM

MOMENTUM. Momentum is a commonly used term in sports. A team that has the momentum is on the move and is going to take some effort to stop.

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MOMENTUM

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  1. MOMENTUM

  2. Momentum is a commonly used term in sports. A team that has the momentum is on the move and is going to take some effort to stop.

  3. Momentum is a physics term; it refers to the quantity of motion that an object has. A sports team which is "on the move" has the momentum. If an object is in motion (on the move) then it has momentum.

  4. Let’s look at some examples of what momentum is. Which will have a greater momentum, a tennis ball served at you by me, or by Pete Sampras? Why ? More force is needed to stop a tennis ball served at 135 mph than one at 75 mph, even though they both have the same mass.

  5. Which has more momentum, a car at 45 mph or a train at 45 mph? Train Why ? More force is needed to stop a train than a car traveling at the same speed.

  6. So…what factors are important for determining the momentum of an object? Both mass and velocity are important factors when considering the force needed to change the motion of an object. This relationship was originally developed by Newton in his 2nd Law.

  7. the product of mass and velocity of an object momentum = mass x velocity ρ = mv

  8. So you got the Mo? • 1. Determine the momentum of a ... • 60-kg halfback moving eastward at 9 m/s. • B. 1000-kg car moving northward at 20 m/s. • C. 40-kg freshman moving southward at 2 m/s.

  9. 2. A car possesses 20 000 units of momentum. What would be the car's new momentum if ... • its velocity were doubled. • B. its velocity were tripled. • C. its mass were doubled (by adding more passengers and a greater load) • D. both its velocity were doubled and its mass were doubled.

  10. An object’s momentum will change if its mass and/or velocity changes. Most common… a change in velocity. What is a change in velocity called? Acceleration a = Vf-Vo t According to Newton’s laws, a net force causes an object to accelerate, or change its velocity.

  11. Newton’s Second Law V t m (Vf-Vo) t m F = ma = = = m v p F t =

  12. Impulse = change in momentum FΔt = m(Vf-Vo) So what does this mean?

  13. A 1000 kg car moving at 30 m/s (p = 30,000 kg m/s) can be stopped by 30,000 N of force acting for 1.0 s (a crash!) or by 3000 N of force actingfor 10.0 s (normal stop)

  14. Possible?

  15. A 0.50-kg cart (#1) is pulled with a 1.0-N force for 1 sec; another 0.50 kg cart (#2) is pulled with a 2.0 N-force for 0.50 seconds. • Which cart (#1 or #2) has the greatest acceleration? Explain. B. Which cart (#1 or #2) has the greatest impulse? Explain. C. Which cart (#1 or #2) has the greatest change in momentum? Explain.

  16. Rhonda, who has a mass of 60.0 kg, is riding at 25.0 m/s in her sports car when she must suddenly slam on the brakes to avoid hitting a dog crossing the road. She strikes the air bag, which brings her body to a stop in 0.400 s. What average force does the seat belt exert on her? If Rhonda had not been wearing her seat belt and not had an air bag, then the windshield would have stopped her head in 0.001 s. What average force would the windshield have exerted on her?

  17. Contact time is reduced if arm's deceleration is kept as small as possible. This is done by using "follow-through", which means to continue to push during the contact period. Some applications of impulse

  18. Spreading impulse out over a longer time means that the force will be less; either way, the change in momentum of the boxing glove, fist, and arm will be the same.

  19. Observe that the greater the time over which the collision occurs, the smaller the force acting upon the object. Thus, to minimize the effect of the force on an object involved in a collision, the time must be increased; and to maximize the effect of the force on an object involved in a collision, the time must be decreased.

  20. For the remainder of class...  PSE Chapter 4 pg 53 #1-6 due BOC 1/6

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