Section 2.4: Forces transfer
momentum
Vocabulary
momentum
• _______________
is a measure of mass
in motion.
If you throw a
tennis ball at a
wall, what would
happen?
If you could throw
a wrecking ball at
a wall, what would
happen?
So…why would a wrecking ball have a different effect on the
wall than the tennis ball?
The wrecking ball will have more momentum than the tennis
ball because the wrecking ball has more ____________!
mass
Thinking Question
• Momentum is similar to inertia,
because it takes into account an
mass
object’s ____________.
• Momentum is dissimilar to inertia
because inertia does NOT take into
velocity
account an object’s ________________
like momentum does.
• An increase in either mass or velocity
___________________
momentum.
increases
• A decrease in either mass or velocity
decreases
_________________
momentum.
Calculating Momentum:
Formula
Momentum = mass x velocity
p = mv
p = momentum
m = mass
v = velocity
Calculating Momentum
Class Example
• What is the momentum of a 1.5 kg ball
moving at 2 m/s?
p = 1.5 kg • 2 m/s
p = 3 kg • m/s
Calculating Momentum
Class Practice Problem #1
• A 3 kg ball is moving with a velocity of
1 m/s. What is the ball’s momentum?
p = 3 kg • 1 m/s
p = 3 kg • m/s
Calculating Momentum
Class Practice Problem #2
• What is the momentum of a 0.5 kg ball
moving 0.5 m/s?
p = 0.5 kg • 0.5 m/s
p = 0.25 kg • m/s
Vocabulary
collision
• A ___________
is a situation in which
two objects in close contact exchange
energy and momentum.
As the second car bumps into the back of the first car the
force pushes the car forward. Some of the momentum of
the second car is transferred to the first car. At the same
time the second car slows down because of the reaction
force from your car. Therefore….
gains
The first car ______
momentum from the
collision, and the second car ________
loses
momentum.
Thinking Question
• If two objects involved in a collision
have very different masses, which one
will have a greater change in velocity?
The one with less mass will have a
greater change in velocity!
Vocabulary
conservation of momentum
• The principle of ______________________
states that the total momentum of a
system of objects does not change, as
long as no outside forces are acting on
that system.
Total momentum
Momentum 2
The forces on the two
cars are are equal and
opposite. Momentum is
transferred from one car
to the other during the
collision.
Momentum 1
Forces in collision
Total momentum
Momentum 2
Momentum 1
Is momentum a vector?
• Yes – it has both size and
direction!
What happens to the momentum
of a bowling ball when it strikes
the pins?
Some of the
momentum
transfers to the
pins, but the total
momentum
remains the same!
Thinking Question
• In a game of pool,
momentum does not
appear to be totally
conserved. What
other outside forces
are acting on the
momentum system?
Friction!
Really….A Hard Thinking
Question
• What is the overall momentum of a system
made up of a 1 kg ball moving south at 2 m/s
and a 1.5 kg ball moving north at the same
speed?
P=1 kg • 2 m/s
P = 2 kg • m/s south
P = 1.5 kg • 2 m/s
P = 3 kg • m/s north
Since they are in opposite directions you should subtract:
3 kg • m/s – 2 kg • m/s
Overall momentum = 1 kg • m/s north