Download Today`s Topic - OnMyCalendar

Today’s Topic
Momentum
Momentum
Momentum is inertia in motion.
p = mv
p = momentum
kg m/s
m = mass
kg
v = velocity
m/s
Momentum
Impulse is the change of momentum.
Momentum
By increasing the time of contact
you will decrease the amount of
force from an impact.
By decreasing the time of
contact you will increase the
amount of force from an
impact.
Momentum
If you want to change an object’s
momentum you must exert an
impulse on the object.
If no net force or impulse acts on a
system, the momentum of the system
can not change.
Momentum
The Law of Conservation of
Momentum
In the absence of an external force, the
momentum of a system remains
unchanged.
The total momentum of a system before
and after an event is the same.
Momentum
Elastic Collision – objects hit each
other and bounce off (KE conserved)
Inelastic Collision – objects hit each
other and stick together (KE lost)
Momentum
A bug hits the windshield
of a fast moving car.
Are the forces of impact on the bug and
the car the same size? Yes
Is the impulse on the bug and the car the
same size? Yes
Momentum
A bug hits the windshield
of a fast moving car.
Are the changes in speed of the bug and
the car the same? No
Are the changes in momentum of the bug
and the car the same size? Yes
Momentum
Granny is skating and
collides with Ambrose who
is standing still. After the
collision, Granny and
Ambrose move together.
What is their velocity after
the collision?
Momentum
pG = mG vG
pG = (80 kg)(6 m/s)
pG = 480 kg m/s
pA = mA vA
Momentum before
pA = (40 kg)(0 m/s)
pB = pG + pA
pA = 0 kg m/s
pB = 480 kg m/s
Momentum
pB = mafter vafter
vafter = pB / mafter
vafter = (480 kg m/s)/(80 kg + 40 kg)
vafter = (480 kg m/s) / 120 kg
vafter = 4 m/s