Momentum
CHAPTER 9
Momentum
• Momentum is a vector quantity defined as the
product of an objects mass and velocity
• Momentum describes an object’s motion
• Symbol for Momentum is p (lower case)
• Note: Uppercase P is Power
• Formula for Momentum is mass x velocity
• p = mv
• Units for momentum are kilogram•meters per
second (kg•m/s)
Momentum
• When we think of a massive object moving at a high
velocity, we often say that the object has a large
momentum.
• A less massive object with the same velocity has a
smaller momentum.
• On the other hand, a small object moving with a very
high velocity has a large momentum.
Momentum
• The faster you move, the more momentum
you have and the more difficult it is to
come to a stop.
• The more massive an object is, the more
force it will exert on another object when
they collide because of its momentum.
Impulse
• Impulse is defined as the product of force
and the time over which an external force
acts on an object.
• Symbol for Impulse is J
• Formula for impulse is Force x change in
time
• J = F∆T
• Units of impulse are Ns or kg•m/s
Impulse-Momentum Theorem
• The Impulse-Momentum Theorem
states a change in momentum takes
force and time.
• Change in Momentum (∆p) = Force x
change in time (F∆T)
• ∆p = pf – pi therefore pf – pi = F∆T
• Since p = mv we can also say
mvf – mvi = F∆T
Impulse- Momentum Theorem
• Stopping time and distances depend on the
impulse-momentum theorem.
• Highway safety engineers use the impulsemomentum theorem to determine stopping
distances and safe following distances for cars and
trucks.
• The impulse-momentum theorem is used to design
safety equipment that reduces the forces exerted
on a human body during collisions
• On a trampoline, jumpers are protected
from injury because the rubber reduces
the force of the collision by allowing it to
take place over a longer period of time.
Egg Impulse Demo
Worksheet 6.A
Conservation of Momentum
• In its most general form, the law of
conservation of momentum can be
stated as follows:
• The total momentum of all objects
interacting with one another remains
constant
• Regardless of the nature of the forces
between the objects, Momentum is
conserved in collisions
Conservation of Momentum
• When two or more objects collide, the
total momentum of the two objects
together remains the same.
• The total initial momentum = the total
final momentum
• M1v1i + m2v2i = m1v1f +m2v2f
• If initially both objects are at rest, then
the initial total momentum = 0
2 major types Collisions
• Perfectly inelastic collisions
• 2 objects collide and then move together as one
mass (coupled).
• Kinetic Energy is not constant
• Some of the energy is converted to sound and
heat (like in a car wreck).
• Elastic collisions
• 2 objects collide and return to their original shapes
with no change in total kinetic energy.
• After the collisions, the objects move off separately.