Excerpts from Chapters 9 and 11 Impulse and Momentum Newtons 2nd Law of motion can be rewritten by using the definition of acceleration as the change in velocity over the change in time ID: 564326
Download Presentation The PPT/PDF document "Momentum & Impulse" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Momentum & Impulse
Excerpts from Chapters 9 and 11Slide2
Impulse and Momentum
Newton’s 2nd Law of motion can be rewritten by using the definition of
acceleration as the change in velocity over the change in time.Slide3
Impulse and Momentum
If the change in time is multiplied out of the denominator, we are left with the following:Slide4
The product of force and change in time is called the
i
mpulse
(symbol is
J
).
Impulse is a
vector
quantity and is measured in Newton-seconds (
Ns
).Slide5
Impulse
If a car hits a haystack or the same car hits a wall, momentum is decreased by same
impulse – the same products of force and time. However, impact force is greater into the wall than it is into the haystack as the haystack extends impact
time
, lessening the impact force.
Impact
time is the time during which momentum is brought to
zero. Slide6
The product of the mass and the velocity is called the
momentum
(symbol
-“rho”) of an object.
Momentum is also a
vector
quantity and is measured in
kgm
/s
.
Note that the units for
impulse
and
momentum
appear different, but they are actually the
same
unit when simplified.Slide7
Momentum
Momentum can be increased with an increase in either
mass or in velocity or both.
Ex: a rolling bowling ball has
greater
momentum than a tennis ball rolling at the same speed because its mass is
greater
Ex: a racecar going forward at 120 mi/hr
has greater momentum than the same size car going 90 mi/hr due to its greater velocity If an object is not moving (no matter how big it is), the momentum is equal to
zero
.Slide8
The
impulse-momentum theorem
states that the impulse on an object is equal to the object’s final momentum
minus
the object’s initial momentum.
Can also be written as:Slide9
Example 1
Tiger Woods hits a 0.050kg golf ball, giving it a speed of 75m/s. What is the impulse given to the ball?Slide10
Example 2
Shane hits a stationary 0.12kg hockey puck with a force that lasts for 1.0x10-2s and makes the puck shoot across the ice with a speed of 20.0m/s, scoring a goal for the team. With what force did Shane hit the puck?Slide11
Example 3
Diana, whose mass is 50.0kg, leaves a ski jump with a velocity of 21.0m/s. What is her momentum as she leaves the ski jump?Slide12
Journal #
What do we mean when we ask people to “conserve water”?What do you think it will mean if we say that momentum is conserved?Slide13
Conservation of Momentum
A system is the environment and all of the objects examined in a problem.
A closed system is a system in which no mass is gained or lost.
An
isolated system
is a system in which the net external force is
zero… no forces acting outside of the system have an effect inside of it.Slide14
Conservation of Momentum
The law of conservation of momentum states that the sum of momentum of any closed, isolated system does
not change… or that the sum of the momentum of the objects in that system is constant.Slide15
Conservation of Momentum
Mathematically, we can view this as a BEFORE and AFTER situation.
For any two objects A and B:Slide16
Types of Collisions
If two objects bounce apart when they collide, it is called an
elastic collision and can be written:
If two objects
stick
together when they collide, it is called an
inelastic collision and can be written:
Slide17
Example 1
Tubby and his twin brother Chubby have a combined mass of 200.0kg and are zooming along in a 100.0kg amusement park bumper car at 10.0m/s. They bump Melinda’s car, which is sitting still. Melinda has a mass of 25.0kg. After the elastic collision, the twins continue ahead with a speed of 4.12m/s. How fast is Melinda’s car bumped across the floor?Slide18
Example 1 Picture
Mel
T&C
Before Collision
Mel
T&C
After CollisionSlide19
Example 1 AnswerSlide20
Example 1 AnswerSlide21
Example 2
If an 800.kg sports car slows to 13.0m/s to check out an accident scene and the 1200.kg pick-up truck behind him continues traveling at 25.0m/s, with what velocity will the two move if they lock bumpers after a rear-end collision?Slide22
Example 2 Picture
Before Collision
After CollisionSlide23
Example 2 AnswerSlide24
Example 2 AnswerSlide25
Journal #
Explain how an airbag protects you by making you come to a stop differently than hitting steering wheel.Try to use the words impulse, force, and time in your answer.Slide26
Journal #
Impulse is a force applied over an interval of time. In this question, the impulse of hitting the steering wheel and hitting the airbag are the same amount because they both cause you to stop. However, the airbag applies a smaller force to your body over a larger time, therefore keeping you safer. Slide27
Journal #
Order these objects from the most momentum to the least.A bullet shot from a rifle
An elephant standing still A bowling ball rollingA fly buzzing by your ear