Chapter-7 Momentum and Impulse

1
Chapter-7 Momentum and Impulse
2
Outline
1 Momentum and Impulse 2 Conservation of
Momentum 3 Recoil 4 Elastic and Inelastic
Collisions 5 Collisions at an Angle Everyday
Phenomenon An Automobile Collision
3
The word momentum in daily life

• Sports to mean changes in the flow of a game
• Elections
• Cheney senses momentum
• Bush Builds Momentum

4
7.1 Momentum and Impulse
A tennis ball bouncing off the floor. There is a
rapid change in the direction of the velocity
when the ball hits the floor.
5
Baseball
Q Why batters swing when they hit a ball?
6
Baseball
Q Why batters swing when they hit a ball? A To
increase the time of contact
7
Catching an Egg

• Q An egg is thrown at you. How can you catch it
  without breaking it?

8
Impulse, J
The impulse J of a force is the product of the
average force and the time interval Dt during
which the force acts
Impulse is a vector quantity and has the same
direction as the average force. SI Unit of
Impulse newton second (N s)
9
Momentum, p
The momentum p of an object is the product of the
objects mass m and velocity v
Momentum is a vector quantity that points in the
same direction as the velocity. SI Unit of Linear
Momentum kilogram meter/second (kg m/s)
10
IMPULSE/MOMENTUM Principle
Impulse Change in momentum When a net force
acts on an object, the impulse of the net force
is equal to the change in momentum of the object
11
A bowling ball and a tennis ball with the same
momentum
12
Bouncing Tennis ball
The floor delivers the impulse to the tennis
ball.
13
Try this box 7.1
14
7.1 Conservation of Momentum
The principle of conservation of momentum helps
us understand collisions such as above.
15
The Principle of Conservation of Momentum
The total momentum of an isolated system remains
constant (is conserved). Isolated means there
are no net external forces. Demo
16
Try this box 7.2
17
7.3 Recoil
Q Why does a shot gun slam against your shoulder
when fired?
18
Rocket Motion
Q How can a rocket accelerate in empty space?
19
Two Skaters Push off
Starting from rest, two skaters push off
against each other on smooth level ice, where
friction is negligible. The mothers mass is 100
kg and the childs is 50 kg. If the mother moves
away with a velocity of 2.5 m/s, west, find the
recoil velocity of the child.
20
(No Transcript)
21
7.4 Elastic and Inelastic Collisions
Collisions are often classified according to
whether the total kinetic energy changes during
the collision 1.Elastic collisionOne in which
the total kinetic energy of the system after the
collision is equal to the total kinetic energy
before the collision. 2.Inelastic collisionOne
in which the total kinetic energy of the system
is not the same before and after the collision
if the objects stick together after colliding,
the collision is said to be perfectly or
completely inelastic.
22
Inelastic Collisions
Partially inelastic collision is one in which
some energy is lost, but the objects do not stick
together after the collision. Perfectly inelastic
collision is one in which the objects stick
together after the collision. A greatest portion
of energy is lost here.
23
(No Transcript)
24
(No Transcript)
25
Try this box 7.4
26
7.3 Collisions at an Angle
27
Vector Diagram
28
An Automobile Collision
29
Analysis
30
Elastic two-dimensional collision