What is Momentum and Impulse ConceptsPowerPoint.ppt

Momentum Review
A parked truck A bicycle pedaled by a boy

Questions:
Which has more momentum, the bicycle or
the truck? Why?
How do we define momentum?

• Are you familiar
with these
pictures?
• Where can we
commonly see
them?

Lesson Objectives:
1. Describe how each factor (force and time)
affects the change in momentum/impulse.
2. Solve simple problems on impulse.
3. Relate the concept of momentum – impulse
relationship on road safety and on some contact
and non-contact sports during collision.

Egg-drop Experiment Demo
Video
Setup A- the egg will be dropped directly on the tile
floor (the tile floor is wrapped with a thin plastic);
Setup B- the egg will be dropped on the tile floor with
a piece of 3.65 cm thick foam on top and a thin plastic.

PROBEX (Predict-Observe-Explain)
1. What do you think will happen to the egg in
setup A? Why?
2. What do you think will happen to the egg in
setup B? Why?

Processing
Setup A Setup B
1. Why did the egg break
in setup A?
2. Why did the egg didn’t
break in setup B?
3. What did the foam had
in setup B which keep the
egg from breaking?

momentum = mass x velocity
p = mv
p = momentum; has units of kg*m/s
m = mass; has units of kg
v = velocity; has units ofm/s

Momentum is a vector,
so direction is important.
An object’s momentum will change
if its mass and/or velocity
(speed and direction) changes.
According to Newton’s laws,
a net force causes an object to accelerate,
or change its velocity.
A net force, therefore, causes a
change in an object’s momentum.

F = ma (Newton’s Second Law)
The formula F = ma can be
broken down into the following
units:
N = (kg)(m/s2)
REMEMBER…

m v
=
p
Impulse = change in momentum
To have a change in momentum there must
be a force applied during a time interval
F t
=
p
(kg)(m/s)
=
p (N)(s)
=
p
Units: Momentum
Momentum equation Impulse equation
Units: Impulse

mvf - mvi
=
pf - pi
F t
=
p
Symbols:
m v
=
p
mvf – mvi = F
Since Δ means “the change in” – we can
rewrite the equation on the left to be:
Now we can combine the two equations into one:

How hard is it to stop a moving
object?
To stop an object, we have to apply a force over a period
of time.
This is called Impulse
Impulse = FΔt Units: N∙s
F = force (N)
Δt = time elapsed (s)

How hard is it to stop a moving
object?
• Using Newton’s 2nd Law we get
FΔt= mΔv
Which means
Impulse = change in momentum

Practice Problem
A 57 gram tennis ball falls on a tile floor. The ball changes
velocity from -1.2 m/s to +1.2 m/s in 0.02 s. What is
the average force on the ball?
Identify the variables:
Mass = 57 g = 0.057 kg
Δvelocity = +1.2 – (-1.2) = 2.4 m/s
Time = 0.02 s
using FΔt= mΔv
F x (0.02 s) = (0.057 kg)(2.4 m/s)
F= 6.8 N

Try to Solve this!
A lady tennis payer hits an approaching ball
with a force of 750 N. If she hits the ball I
0.002 s, how much impulse is imparted to the
tennis ball?

Given:
F= 750 N
t= 0.002 S
Required: Impulse (I)
Solution:
I=Ft = 750 N (0.002 s)
I = 1.5 N.s

Why does an egg break or not break?
• An egg dropped on a tile floor breaks, but an egg
dropped on a pillow does not. Why?
FΔt= mΔv
In both cases, m and Δv are the same.
If Δt goes up, what happens to F, the force?
Right! Force goes down. When dropped on a pillow,
the egg starts to slow down as soon as it touches it.
A pillow increases the time the egg takes to stops.

Impulse Application
Why do we need safety devices like seatbelts
and helmets?
Can you think of other safety devices used in
automobiles/cars?

The greatest change in
velocity will occur when
the impulse is the greatest.
By increasing the amount
of force and the amount of
time the force is applied,
the greatest change in
velocity can be achieved.

A 1000 kg car moving at 30 m/s (p = 30,000 kg*m/s)
can be stopped by
30,000 N of force acting for 1.0 s (a crash!)
or
by 3000 N of force acting for 10.0 s (normal stop)

Concept Check
Write I if the impact time is smaller and O if the impact
time is bigger.
1. A quick jab by Pacman makes a hard hit.
2. A net used to catch mango fruit.
3. Jet Li severs a piece of wood to cut in half.
4. WWF wrestler spreads his arms and legs as he hits the ground.
5. A kid practices back tumbling in a pile of haystack.

What is Momentum and Impulse ConceptsPowerPoint.ppt

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