Impulse and Momentum

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Transcript Impulse and Momentum

Objectives
Students should be able to:
1. Define linear momentum and calculate it.
2. Distinguish between the unit of force and
momentum.
3. design an experiment in order to make
conclusions about the total momentum in a
system before and after a collision or
explosion.
Let’s start with everyday
language
What do you say when a sports team
is on a roll?
They may not have the lead but they
may have ___________
MOMENTUM
A team that has momentum is hard to
stop.
Momentum Defined
p = mv
p = momentum
vector
m = mass
v = velocity vector
Momentum
• Momentum depends on the mass of an
object and the speed it is going.
– Momentum = mass x velocity
• Because velocity has direction then
momentum does, also.
Momentum of Objects
• Put the following in the order of most
momentum to least:
–
–
–
–
–
Mosquito
Automobile
Space Shuttle
Bullet
Freight Train
Questions
• Does a small object always have less
momentum than a large one?
• How can a bullet from a rifle knock over
an animal?
Which has more momentum?
• A truck or a roller skate rolling down a hill
with the same speed?
• A truck stopped at a light or a marble
rolling down the road?
• When could the roller skate and the truck
have the same momentum?
What is Momentum?
An object with a lot of momentum is also hard to
stop
Momentum = ρ = mv
Units: kg∙m/s
m=mass
v=velocity
Momentum is also a vector (it has direction)
Momentum
MASS
Momentum is _________
in
MOTION
________.
Momentum is a vector quantity.
Momentum is dependant on the
VELOCITY
mass and the ___________
of
an object.
Momentum Facts
• p = mv
• Momentum is a vector quantity!
• Velocity and momentum vectors point in the same direction.
• SI unit for momentum: kg·m/s (no special name).
• Momentum is a conserved quantity (this will be proven later).
• A net force is required to change a body’s momentum.
• Momentum is directly proportional to both mass and speed.
• Something big and slow could have the same momentum as
something small and fast.
Momentum Examples
10 kg
3 m/s
10 kg
30 kg · m
/s
Note: The momentum vector does not have to be
drawn 10 times longer than the velocity vector,
since only vectors of the same quantity can be
compared in this way.
26º
5g
p = 45 kg · m /s
at 26º N of E
Equivalent Momenta
Car: m = 1800 kg; v = 80 m /s
p = 1.44 ·105 kg · m /s
Bus: m = 9000 kg; v = 16 m /s
p = 1.44 ·105 kg · m /s
Train: m = 3.6·104 kg; v = 4 m /s
p = 1.44 ·105 kg · m /s
continued on next slide
Equivalent Momenta
(cont.)
The train, bus, and car all have different masses and
speeds, but their momenta are the same in magnitude. The
massive train has a slow speed; the low-mass car has a
great speed; and the bus has moderate mass and speed.
Note: We can only say that the magnitudes of their
momenta are equal since they’re aren’t moving in the
same direction.
The difficulty in bringing each vehicle to rest--in terms of a
combination of the force and time required--would be the
same, since they each have the same momentum.
Newton’s Law and Momentum
• Newton’s Second Law can be used to relate the
momentum of an object to the resultant force
acting on it
• The change in an object’s momentum divided
by the elapsed time equals the constant net
force acting on the object
March 26, 2016
Problem
 A 1200 kg car drives west at 25 m/s for 3 hours.
What is the car’s momentum?
 Identify the variables:



1200 kg = m
25m/s, west = v
3 hours = t
p = mv
p = (1200kg)(25m/s) = 30000 kgm/s, west
Homework
• Be ready with your procedure for next class.
Leading to Inquiry for Total
Momentum of a System Before
and After a Collision or explosion
 Each group will have a different type of
collision or explosion. Some will overlap
since we will focus on three types of
collisions/explosions.
Momentum – Elastic Collisions period 5 start here
 Elastic Collision – a collision in which the colliding bodies do not
stick together.
© 2001-2007 Shannon W. Helzer. All Rights Reserved.
Momentum – Inelastic Collisions
 Inelastic Collision – a collision in which the colliding bodies stick
together.
© 2001-2007 Shannon W. Helzer. All Rights Reserved.
Explosions
M
v1
m1
“before”
m2
v2
“after”
Momentum
 Identify the number and types of collisions in the animation below.
© 2001-2007 Shannon W. Helzer. All Rights Reserved.
Momentum
 Identify the number and types of collisions in the animation below.
© 2001-2007 Shannon W. Helzer. All Rights Reserved.
Momentum
 Identify the number and types of collisions in the animation below.
© 2001-2007 Shannon W. Helzer. All Rights Reserved.
Inquiry for Total Momentum Before
and After a Collision/Explosion
• PROBLEM
• Design an experiment to demonstrate the
effect of a collision/explosion on total
momentum of the objects before and after
using the same mass for each cart and then
for a second experiment change one of the
cart’s mass by adding mass.
Inquiry for Total Momentum Before
and After a Collision/Explosion
• Design an experiment to demonstrate the effect of a collision/explosion
on total momentum of the objects before and after using the same mass
for each cart and then for a second experiment change one of the cart’s
mass by adding mass to it.
• Make a prediction on the effect of some condition on the
total momentum before and after a collision.
• Materials
–
–
–
–
–
–
Dynamics cart with spring bumper or plunger
Meter stick
Stop watch
Masses
Large white boards
Ramp
Inquiry for Total Momentum Before and After
a Collision/Explosion
• Your group will present using the whiteboards your
design and findings.
• What did you discover about the momentum before and after a collision
or explosion?
• What happened to the momentum before and after when one of the carts
had more mass?
• Were any of the results NOT what you expected?
• Did the data support your original prediction?
Evaluation
• Individually, you will write an analysis about the investigation
with supporting evidence, and then explain how the
conservation of momentum can be applied to the
investigation.
• Describe the investigation and the theoretical concepts
related to the investigation.
• Can you test the predictions? What conclusion(s) did you
reach due to the results of this experiment? If so, do results
agree with your conclusion(s)?
• What evidence (text and/or data) supports your
conclusion(s)?
• Are your results reliable? What were the sources of error and
how did you compensate for sources of error in the
experiment?
• This will be due 3 days after the conclusion of the
investigations.
Conclusions
• Based on the investigations, what conclusion
can you make about the momentum in a
system?
• Kahoot