Do Now
• I am not collecting HW today. Take back your quiz
• I can guarantee you will see these questions again
(midterm, Quest, etc.)
• Go through your HW, notes (Do Now’s, Exits,
POGILs, etc) and HIGHLIGHT where you can find
the solutions to every one of your quiz questions
(for the majority of them, it’s word for word)
• As you are highlighting, MAKE CORRECTIONS.
• Check in with me when you are stuck.
Question
2 cars are involved in a collision. Which would be more
damaging - if the cars collide and bounce or collide and
crumple?
Collide and bounce. The momentum change is larger and
therefore there is a greater impulse and greater force.
Question
What are two ways that crumple zones in cars minimize the
effect of force in a collision?
1. Crumpling increases the time over which the momentum
is changed, thus decreasing the force.
2. Crumpling means less likely to rebound, thus less impulse.
Question
Why is falling on a floor with more give less
dangerous than falling on a floor with less give?
The floor with more give allows a greater time for the
impulse that reduces the momentum of the fall. A
greater time for changing momentum means less force.
Take out your
Elastic and
Inelastic
collision notes
from last class.
We are now
going to define
what these
collisions
actually are.
(turn the page)
Qualities
Describe how they
collide – bounce,
stick together, etc…
ELASTIC
Bounce
INELASTIC
Stick
What happens to
Always conserved!
the momentum
after collision? Is it **It’s the LAW**
conserved? Is it
shared, or
transferred…
Are the objects
Nope!
deformed postcollision?
Always conserved!
Is heat generated
during the
collision?
No – there is no such thing as
perfectly elastic collision that we
can SEE, because there is always
SOME friction
Yes – friction!
Give real life
examples:
TECHNICALLY…Subatomic
particles colliding
TECHNICALLY…Everything we
can see with our bare eyes
**It’s the LAW**
Yep! As long as there is no external
force, there is no way to get them
back to normal…
But the closest thing we can see But the closest thing we can see
to it would be something like
to it would be something like a
billiards
car crash
Series of questions from your HW last
night…
• Heads down, 1-2-3 answers
If 2 objects of EQUAL mass experience
an ELASTIC collision…
1. Momentum IS
conserved
2. Momentum IS NOT
conserved
3. Not quite sure
If 2 objects of UNEQUAL mass
experience an ELASTIC collision…
1. Momentum IS
conserved
2. Momentum IS NOT
conserved
3. Not quite sure
If 2 objects of EQUAL mass experience
an INELASTIC collision…
1. Momentum IS
conserved
2. Momentum IS NOT
conserved
3. Not quite sure
If 2 objects of UNEQUAL mass
experience an INELASTIC collision…
1. Momentum IS
conserved
2. Momentum IS NOT
conserved
3. Not quite sure
Key Point?
Momentum is ALWAYS conserved, in both
ELASTIC
and
INELASTIC
collisions
Momentum is a conserved quantity in physics.
This means that if you have
an object or several objects in
a system, interacting with
each other, but not being
influenced by any forces from
outside of the system, then
the total momentum of the
system does not change over
time.
11
Law Of Conservation Of Momentum
In the absence of an external force, the momentum
of a system remains unchanged.
The momentum lost by an object in a closed system will be
gained by other objects so that the total
momentum will remain the same in the system.
Closed System: No matter or energy is allowed to enter or leave the system.
The separate momenta of each object within the system may
change.
One object might change momentum, while another object changes
momentum in an opposite manner, picking up the momentum that
was lost by the first.
Conservation of Momentum
Momentum = 0 before the shot
And after the shot
Cannon’s
momentum
Shell’s momentum
(equal and opposite)
Before collision:
1. The momentum of the cart is 60 kg*cm/s
2. The momentum of the dropped brick is 0 kg*cm/s
3. The total system momentum is 60 kg*cm/s.
After collision:
1. The momentum of the cart is 20.0 kg*cm/s
2. The momentum of the dropped brick is 40.0 kg*cm/s
3. The total system momentum is 60 kg*cm/s.
4. The momentum lost by the loaded cart (40 kg*cm/s) is gained by the
dropped brick.
In hockey…Momentum is transferred from the stick to
the puck. The momentum lost by the stick is equal to the
momentum gained by the puck. The total amount of
momentum stays the same.
Or…Momentum is transferred from player to player.
(The momentum lost by one player is equal to the momentum
gained by the other. The total amount of momentum stays the
same.)
Go to this
Page in your
Pogil 
Remember…key point is
MOMENTUM BEFORE = MOMENTUM AFTER
Fill
this
in!!!
Elastic 
INelastic

We are going to try one together…
(80 * 3 ) + (42 * 0)
(240) + (0)
= (80 + 42 ) vf
= (122) vf
240 kg m/s = (122 kg) vf
Divide both sides by 122 kg, and
vf = ~ 2m/s
Data from Collision Java Activity
• Take out your data from last class
• Pick your data from ONE of the ELASTIC
COLLISIONS and check via formula.
• Repeat with data from ONE of the INELASTIC
COLLISIONS and check via formula.
BEFORE
Mass of Wagon 1
Mass of Wagon 2
AFTER
Mass of Wagon 1
Mass of Wagon 2
Velocity of Wagon Velocity of Wagon Velocity of Wagon Velocity of Wagon
1
2
1
2
Total Momentum:
Total Momentum:
Quest Prep
• I am not collecting these, but here are your options for
Quest Prep… (all worksheets also online)
• Want more practice with conservation of momentum
formula? On the back of your web quest, try the
problems listed (p. 100, #22, 27, 35, 37)
• Need more math practice in general, including
conservation of momentum? Go here for problems AND
written as well as spoken solutions (also linked on my website)
tinyurl.com/RHSmomentumMATH
Or try these on page 101-102: #24, 29, 32, 34 & 36
• Need more conceptual practice? Finish the back
of the Granny/Ambrose worksheet, and see me
for another conceptual review worksheet