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Momentum and Impulse

Momentum and Impulse. What is momentum? (p). 2 Definitions Momentum – the impetus of a body resulting from it’s motion. Impetus – the force or energy associated with a moving body So, momentum is a measurement of how energetically a body is moving. Anything that is moving has momentum.

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Momentum and Impulse

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  1. Momentum and Impulse

  2. What is momentum? (p) • 2 Definitions • Momentum – the impetus of a body resulting from it’s motion. • Impetus – the force or energy associated with a moving body • So, momentum is a measurement of how energetically a body is moving. Anything that is moving has momentum. • Think of momentum as the “oomph” that a moving body has when it collides with another object. • Mathematically we define it as follows (p – variable for momentum) or

  3. Calculating momentum • Calculating momentum • A 5.8 g bullet is traveling at 975 m\s. What is it’s momentum? • Sometimes an object’s momentum changes based on what happens during it’s movement. • A 150 Kg roller coaster car is initially traveling at 25 m/s. Over time, friction causes it to slow 20 m/s. What is the change in it’s momentum? • p=mv p= (.0058)(975) p= 5.7 kg*m/s (don’t forget to convert g to kg) • Δp = mΔv Δp = (150)(20 - 25) = 150(-5) = -750 kg*m/s

  4. How does an object “get” momentum? • For an object to have momentum, it must be moving. Therefore, non-moving objects must become moving objects to have momentum. • To begin (or change) an object’s movement, an unbalanced force must be applied. The stronger the unbalanced force the more it changes the object’s momentum. In addition, the longer the period of time that the unbalanced force is applied the more momentum the object will have. FU increased a increased v increased p or FU decreased a decreased v decreased p

  5. Impulse (Δp) • Anything that causes a change in an object’s momentum is called an impulse. • Impulses are unbalanced forces acting upon the object for a certain period of time. • Mathematically, impulse (Δp) can be expressed in 2 ways. or • Since FΔt and mΔv are both expressions of impulse they may be set equal to each other. This is called the momentum-impulse theorem, and it is expressed as FΔt = mΔv .

  6. Using the momentum-impulse theorem • A 75 kg man jumps out of a 50 m tall window. He is traveling at 31.3 m\s at the instant before he hits the ground. The parking lot brings him to a stop in .001 s. A second 75 kg man jumps out of the same window and an airbag brings him to a stop over the course of 1.5 s. Which one has the greater chance to survive the fall? • First, calculate his momentum before the man hits the ground p=mv=(75)(31.3)=2347.5 kg*m/s • Then calculate the force he hits the ground\airbag with. FΔt = 2347.5 F(.001) = 2347.5 F = 2,347,500 N • Now do the same calculations for the second man. (1565 N)

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