Warm-up by yurtgc548

VIEWS: 4 PAGES: 12

									           Warm-up:
    Which of these objects would be
         the hardest to stop?

   1500 m/s                 25 m/s

.02 kg bullet         10 kg bowling ball


   3 m/s                   3×108 m/s

80 kg running back      2×10-27 kg neutron
       Dimensional Analysis WS
   Any questions?
                Momentum
We have learned that inertia determines how
 difficult it is to change an object’s state of
 motion, but there is more to the story. We must
 also consider the velocity of the object.


Momentum – a measure of how hard it is to
 stop a moving object.
                  Momentum
Calculating momentum:
     Momentum = mass × velocity
     Equation: p = mv

   Units of momentum are (kg)(m)/s

   Note that when an object is standing still (v=0),
      it has no momentum.
                Momentum
Use p = mv to calculate the momentum of each
 of the objects from the Warm-up problem.

Which one really is the hardest to stop?
           Warm-up:
    Which of these objects would be
         the hardest to stop?

   1500 m/s                 25 m/s

.02 kg bullet         10 kg bowling ball


   3 m/s                   3×108 m/s

80 kg running back      2×10-27 kg neutron
               Momentum
Now we know how to find out which object is the
 hardest to stop, but we still don’t know how
 much force you would experience when you
 were stopping them.

Q: How do you win a water-balloon toss?

A: You change the balloon’s momentum slowly.
                Momentum
Impulse – when a force is exerted over a period of
  time, causing a change in momentum.

We need another equation to determine the forces
 that are exerted while changing an object’s
 momentum:
                F(t) = m(Δv)

     Impulse              Change in momentum
            Impulse in action…
Example #1: Hitting a homerun

You must make the ball gain momentum by:

 A) hitting it hard:   F ( t)   (strength)

 B) extending contact time: F( )   t    (technique)

Why are there so few opposite field home runs?
           Impulse in action…
Example #2: Falling out of a window and landing
 on…

 A) …Concrete:   F ( t)       (stopped in a small
                                    amount of time)

 B) …a Trampoline: F( )   t      (stopped in a large
                                    amount of time)
           Impulse in action…
How else do we minimize force by increasing the
 time of impact?

 A. padded dashboards
 B. seatbelts and airbags
 C. helmets
 D. bungee cords and climbing ropes
 E. sand-filled barrels on the freeway
             Impulse in action…
Practice Problem: If you exert a 300N force on a
  .08 kg golf ball for .04 seconds, how fast will the
  golf ball fly?

     F    (t) = m (Δv)
  (300N)(.04s) = (.08kg) v
            12 = .08 v
              v = 150 m/s

								
To top