Transcript Impulse and Collisions

QW
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What is the unit for momentum?
How do you tell if something is harder to
stop?
If velocity is increased, and momentum
remains the same, what happens to
mass?
What is the difference between inertia
and momentum?
What does magnitude mean?
What is the difference between vector
and scalar?
Impulse
Impulse

Unikitty and Batman are coming toward
you, who is harder to stop?
m= 3 kg
v= 1 m/s
m= 90 kg
v= 1 m/s
Impulse

But, how do you stop Batman?
Impulse

In order to stop Batman (or anything else)
you must apply a force.

When you stop something, you are
changing it’s momentum.
Impulse
A
change in momentum created by a
force exerted over time is called
impulse.
 Basically,
impulse is a change in
momentum.
Impulse
If the momentum of an
object changes, either the
mass, the velocity, or
both change
Impulse
Which do you think is
more likely to change:
the mass of an object, or
the velocity of an object?
Impulse
If the mass remains
unchanged, which is most
often the case, then the
velocity changes and
WHAT occurs?
Impulse
Acceleration
 Remember:
in velocity
acceleration is a change
Impulse
What produces
acceleration?
Impulse
Force
Impulse
The greater the force acting
on an object, the greater its
change in velocity, and
therefore, the greater its
change in momentum
Impulse
How
long the force acts is
also important.
If
you apply a brief force to a
stalled car you changed the
car’s momentum.
Impulse
If you applied the same force
over an extended period of
time you will produce a
greater change in the car’s
momentum.
Impulse
A force sustained for a longer
time produces more change
in momentum than does the
same force applied briefly.
Impulse
BOTH Force and Time are
important in changing
momentum.
Impulse - examples

Boxers attempt to move with an
opponent’s punch when it is thrown. In
other words, a boxer moves in the same
direction as their opponent's punch. This
movement may prevent a knockout blow
being delivered by their opponent. Explain
how.
Impulse - examples
If the force applied by the opponent's
punch can be extended over a longer
time, the force of the blow is reduced,
minimizing the chances of a knockout
punch being delivered to the boxer.
Impulse - examples
 An
egg dropped on a tile floor
breaks, but an egg dropped on a
pillow from the same height does
not.
 Why?
Impulse - examples

In both cases, the mass and velocity are
the same. In this type of example, if the
amount of time the object is in contact
with the force goes up, then the amount
force goes down.

When dropped on a pillow, the egg starts
to slow down as soon as it touches the
pillow. The pillow increases the amount of
time it takes the egg to stop.
Can you throw an egg, and not break it?
https://www.youtube.com/watch?v=7RSUjxi
ZnME
Impulse
In physics, the quantity
Force • time is known as
impulse.
Impulse
Impulse = change in momentum
This is how it looks on your STAAR chart:
Units?
Both sides are Impulse:
Impulse = Ft
J = Ft
Impulse = m(vf-vi)
J = m(vf-vi)
So you will be expected to solve using either side, but
sometimes you will have to use the entire formula.
Impulse – practice problem
A net force of 25 newtons is applied to a 20
kilogram cart for 2 seconds?
What is the impulse?
What is the change in momentum?
Impulse – practice problem
A net force of 25 newtons is applied to a 20
kilogram cart for 2 seconds?
What is the impulse?
F= 25 N
Impulse=Ft
m= 20 kg
(25)(2)=50 N*s
t= 2 s
What is the change in momentum?
50 kg*m/s
Impulse – guided practice
A net force of 30 newtons is applied to a 10
kilogram cart that is already moving at 1
meter per second. The final speed of the
cart was 2 meters per second. For how long
was the force applied?
Impulse – guided practice
A net force of 30 newtons is applied to a 10
kilogram cart that is already moving at 1
meter per second. The final speed of the
cart was 2 meters per second. For how long
was the force applied?
F= 30 N
m= 10 kg
vi= 1 m/s
vf= 2 m/s
Ft = m(vf-vi)
(30)(t)=(10)(2-1)
30t=10
t=.3 s
Impulse – practice problem
A 0.045 kg ball is thrown (from rest) with a
force of 450 N. If the force acts on the ball
for 12 s, what is the final speed of the ball?
Impulse – practice problem
A 0.045 kg ball is thrown (from rest) with a
force of 450 N. If the force acts on the ball
for 12 s, what is the final speed of the ball?
F= 450 N
m= .045 kg
vi= 0 m/s
t= 12 s
Ft = m(vf-vi)
(450)(12)=(.045)(vf-0)
5400=(.045) vf
120,000 m/s =vf
Impulse – practice problem
A .5 kg frisbee is thrown from rest to a final
speed of 12 m/s. What is the impulse of the
frisbee?
Impulse – practice problem
A .5 kg frisbee is thrown from rest to a final
speed of 12 m/s. What is the impulse of the
frisbee?
m= .5 kg
vi= 0 m/s
vf= 12 m/s
J = m(vf-vi)
J =(.5)(12-0)
J = 6 kg*m/s
Impulse-Practice Problem

A tennis player hits a ball during a tennis
match. Compared to the magnitude of the
impulse given to the ball, the magnitude
of the impulse given to the bat is?
A) Same
 B) More
 C) Less

Impulse-Practice Problem

A tennis player hits a ball during a tennis
match. Compared to the magnitude of the
impulse given to the ball, the magnitude
of the impulse given to the bat is?

A) Same