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Momentum and
collisions
Mrs Eman Zaki
Objctives
01
03
Introduction
You can describe the
topic of the section here
Our team
You can describe the
topic of the section here
02
04
Activities
You can describe the
topic of the section here
Conclusions
You can describe the
topic of the section here
Can You Explain the
EXPLAIN
A car collides with a tree,
causing the airbag in the
steering wheel to deploy.
Describe what happens to
the driver and passengers
as the airbag deploys and
their car suddenly comes
to a stop
The airbag rapidly
inflates, cushions the
driver and passengers,
and slows their
forward motion during
the collision.
In an accident, the airbag rapidly inflates to protect the driver and the
passengers.
Momentum
Moving objects all have a property called
momentum, which can be used to quantify how
hard it is to change their motion.
The momentum of an object is related to the
amount of force needed to change the object's
motion in a given amount of time.
The symbol used
in physics for momentum is the variable (p).
The units of momentum are kilogram meters
per second, kg·m/s
Momentum
unit =
kg·m/s
Momentum and Newton’s second law
The momentum of a
particle is the product
of its mass and its
velocity:
The truck and car have the same momentum. Assuming the
brakes are the same and the drivers applied the brakes in the
same way, the vehicles would be equally hard to stop.
The momentum of an object is
directly proportional to both that
object’s mass and its
velocity. If two objects have the same
momentum but different masses,
then the object
with the smaller mass must have a
greater velocity.
More massive objects can have large amounts of momentum
even when they are moving at low velocities. Less massive
objects must be moving at higher velocities to have the same
amount of momentum as a more massive object.
Momentum
• The momentum of a ball depends on its
mass and velocity.
• Ball B has more momentum than ball A.
Momentum
Ball A is 1 kg moving 1m/sec,
• Ball B is 1kg at 3 m/sec.
• If a 1 N force is applied to deflect each ball's motion.
• What happens?
• Does the force deflect both balls equally?
•
 Ball B deflects much
less than ball A when
the same force is
applied because ball B
had a greater initial
momentum.
Calculating Momentum
 The momentum of a moving object
is its mass multiplied by its
velocity.
 That means momentum increases
with both mass and velocity.
Momentum
(kg m/sec)
Mass (kg)
p=mv
Velocity (m/sec)
Comparing momentum
A car is traveling at a velocity of 13.5 m/sec
(30 mph) north on a straight road. The
mass of the car is 1,300 kg.
A motorcycle passes the car at a speed of
30 m/sec (67 mph). The motorcycle (with
rider) has a mass of 350 kg.
Calculate and compare the momentum of
the car and motorcycle.
You are asked for momentum.
You are given masses and velocities.
Use: p = m v
Solve for car: p = (1,300 kg) (13.5 m/s) = 17,550 kg m/s
Solve for cycle: p = (350 kg) (30 m/s) = 10,500 kg m/s
The car has more momentum even though it is going much slower.
Momenta
Car: m = 1800 kg; v = 80 m /s
Bus: m = 9000 kg; v = 16 m /s
p = 144, 000 kg · m /s
p = 144 ,000 kg · m /s
Train: m = 3.6 ·104 kg; v = 4 m /s
p = 144,000 kg· m /s
8.1 Momentum
A truck rolling down a hill has more momentum than a roller
skate with the same speed. But if the truck is at rest and the
roller skate moves, then the skate has more momentum.
2480 kg.m/s to the south
46.5 m/s to the east
Classroom Practice
●
●
●
●
A 1000 kg car has a velocity of 30 m/s to the west.
What is the momentum of the car?
30 000 kg•m/s to the west
A 0.17 kg ball has a momentum of 1.87 kg·m/s to the
south. What is the velocity of the ball?
11 m/s to the south
Conservation of momentum
I think the ice skater who is pushed will move away from the
skater who does the pushing. I could compare the momenta
of both objects before and after the push.
https://www.youtube.com/watch?v=DxKelGugDa8
01
Lets investigate
https://phet.colorado.edu/sims/html/collisionlab/latest/collision-lab_en.html
https://interactives.ck12.org/simulations/physics/bumpercars/app/index.html?screen=sandbox&lang=en&referrer=ck
12Launcher&backUrl=https://interactives.ck12.org/simulatio
ns/physics.html
How to design a case to
make the velocity of the
cart 4 times the velocity
of the other cart
During Part 1, the carts always moved away from each other. How fast they moved
depended on the masses of the carts. The more mass a cart had, the slower it moved
after the spring was released
we found that the average velocity of the heavier cart was always lower than the
average velocity of the lighter cart. If we have the velocity of one cart, we can predict
the velocity of the other cart using the concept of conservation of momentum.
when one skater pushes on another, both skaters will
move away from each other. note that the heavier skater
will move more slowly than the lighter skater.
7-2 Conservation of Momentum
During a collision, measurements show that the
total momentum does not change:
https://www.youtube.com/watch?v=Fp7D5D8Bqjc
7-2 Conservation of Momentum
More formally, the law of conservation of
momentum states:
The total momentum of an isolated system of
objects remains constant.
Homework
Short research
Short summary
How momentum is conserved in
explosions includes (videos,
websites, visual illustrations)and
from a short slide show
Write a short summary for the
pervoius lesson
Collisions
where two or more objects exert forces on one
another
over a relatively short period of time.
eBoo
k
Unit 2 Lesson 1
28
Collisions
• When objects collide,
momentum can be
transferred between them.
COLLABOARATE
Two billiard balls hitting each
other is a collision.
With a partner, use a large piece of
paper and pens of different colors to
model conditions before and after a
collision. Generate the ideas of what
the system is in terms of what forces
are acting on the objects in the
system.
29
Collisions
Unit 2 Lesson 1
Systems and System Models
ANALYZE
Describe a situation in which the
momentum of two billiard balls
would not be conserved. Your
description should include the
limits of the system.
If an external force acts on the balls, such
as hitting one of the balls with a pool cue
or stopping one of the balls with your
hand, momentum would not be
conserved because a force from outside
the system acted on at least one of the
balls
Unit 2 Lesson 1
30
Conservation of
Momentum
• When a collision
between two objects
occurs in a system
with no net external
forces acting on it, the
total momentum of
the objects before the
collision is equal to
the total momentum
of the objects after
the collision.
The white ball gives momentum to the red ball in an amount
equal to the white ball’s loss of momentum. Internal forces do
not change the momentum of the system.
31
Collisions
Before | Two people are at rest.
MODEL
The photos show two people on roller skates
that are facing each other and touching hands.
At the same time, they push against each
other and roll away from each other in
opposite directions. Write equations to
represent the initial and final momentum of
the system of the two skaters.
Are pi and pf equal to each other?
Unit 2 Lesson 1
After | Two people push away
from each other.
Pi = p1 + p2 =0; pf = p1 + p2 = m1v1 + m2v2
The quantities of pi and pf are equal because
m1v1 = –m2v2.
pi = 0 = pf
√
Types of collisions
Perfectly Inelastic
Elastic collision
Inelastic collision
collision
Elastic collision
●
●
Collisions where objects bounce off of
one another and kinetic energy ,there
is no loss of velocity and the objects
return back to their original shapes
after impact. Momentum is
conserved
The total kinetic energy of the objects
before the collision equals the total
kinetic energy of the objects after the
collision.
Inelastic collision
●
Most collisions observed in everyday
life are actually inelastic collisions. In
an inelastic collision, two objects
bounce off of one another, and while
momentum is still conserved, kinetic
energy is not. In these collisions,
energy is often lost from the system
through some combination of
deformation, friction, and sound.
37
Collisions
Unit 2 Lesson 1
Watch what happens in an inelastic collision between a skateboarder
and a backpack. Notice changes in the velocity of each.
APPLY
What do you expect to happen after the collision of the skateboarder
and the backpack?
Perfectly Inelastic collision
●
In a perfectly inelastic
collision, two objects stay
together after colliding.
Momentum is conserved,
but kinetic energy is not.
√
●
EXPLAIN Two billiard balls hitting one another can be modeled
as an elastic collision, and a skateboarder picking up a backpack
can be modeled as a perfectly inelastic collision. Summarize the
differences between elastic, inelastic, and perfectly inelastic
collisions using these examples to help illustrate the differences.
Elastic collisions such as the instance of two billiard balls
colliding conserve both kinetic energy and momentum, and
neither object suffers deformation. Inelastic collisions only
conserve momentum as total kinetic energy before the
collision and after the collision are not equal. Perfectly inelastic
collisions involve the objects changing their shapes and
deforming together, which occurs when the skateboarder and
the backpack become one combined mass.
3.8 m/s to the south
. 1.8 m/s
. a. 3.0 kg
b. 5.3 m/s
38 kg
–1.43 m/s, backward
In all three cases, some
of the kinetic energy of
the moving bumper car(s)
is lost. When the bumper
car collides with the
barrier, most of the
momentum is transferred
back to the bumper car,
so the driver feels the
strongest jolt.
√