# Warm-up by yurtgc548

VIEWS: 4 PAGES: 12

• pg 1
```									           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?

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