Download momentum

Momentum and Its
Conservation
chapter 9
From our textbook
Pages 198-221
Momentum
Commonly used in terms of sports
(i.e. The team has a lot of momentum before
the big championship game)
The team with momentum is “on the move” and
will be hard to defeat.
Momentum
 Momentum is also a physics term.
Momentum- the quantity of motion that an object
has;
All objects have mass, so if an object is moving, it
has momentum (“mass in motion”)
The amount of momentum an
object has is dependent on two
variables:
MASS- How much is moving
(weight)
VELOCITY-How fast the it is
moving
(speed)
Momentum Equation
The momentum of an object is equal to the
mass of the object times the velocity of the
object
Momentum = Mass times Velocity
IMPULSE
The product of the average force and the
time interval over which it acts.
Unit of measurement is Newton-second
(N * s)
The impulse on an object is
equal to the change in
momentum that it causes.
Also Known As…
Impulse-Momentum Theorem
Impulse = Momentum
Using the Impulse-Momentum
Theorem in real life:
Example:
 If a car is traveling at a
fast speed and is
suddenly stopped by a
thick brick wall, how will
its momentum and
impulse affect it?
An impulse is needed to bring the driver’s
momentum to zero.
What can be used to
decrease the force
exerted on the driver?
An AIR BAG is used to reduce the force
exerted on the driver by greatly increasing
the length of time the force is exerted.
To Explain:
 The initial velocity is
the same with or
without the airbag.
 The air bag is used to
reduce the force by
increasing the time it
takes the driver to hit
the steering wheel.
It’s time to go to work:
What is the momentum of a 16 kg bowling
ball rolling at 4 m/s?
momentum = mass * velocity
What we know:
• M = 16 kg
• V = 4 m/s
16 kg * 4 m/s = 64 kg * m/s
= 64 N
More Fun Work:
Multi-Step Problem!
A. What is the momentum of a 50 kg box
that moves 8 m/s across a table?
What we know:
M = 50 kg
V = 8 m/s
• Momentum = 50 kg * 8 m/s
= 400 N
 B. The moving box hits a pillow and stops in .5 seconds.
What is the average force it exerts on the pillow?
 **remember** F (delta) t = m*v
 What we know:
• t = 0.5 s
• M = 50 kg
• V = 8 m/s
 F (0.5s-0s) = 50 kg * 8 m/s
F (0.5s) = 400 N
F = 800 N
C. What average force does the pillow
exert on the box?
800 N
The same force used to stop the box
The same equation is used
9.2 The Conservation
of Momentum
Pages 207- 216
Two- Particle Collision!
According to Newton’s third law of motion,
if two balls collide, despite different
velocities and sizes, the forces exerted on
each other will be equal and opposite.
Two- Particle Collision!
During the collision, the two balls quickly
exert a force on the other.
The time intervals over which the forces
are exerted are the same so they must be
equal in magnitude but opposite in
direction.
It’s Time to go to Work!
Multi-step problems
A 10 kg monster walking 1 m/s eats a 1
kg monster at rest. (A.) What is the speed
of the bigger monster immediately
afterwards?
10 kg * 1 m/s = 10 kg * m/s
1 kg * 0 m/s = 0 kg * m/s
10 kg * m/s
(10 kg + 1 kg) * v = 10 kg * m/s
v = 10/11 m/s
(B.) What would its speed be if the smaller
monster were walking toward the bigger
one 8 m/s?
10 kg * 1 m/s = 10 kg * m/s
1 kg * 8 m/s =- 8 kg * m/s
2 kg * m/s
11 kg * v = 2 kg * m/s
v = 2/11 m/s
The End.
Mr. Arbo! Give me an A!