Transcript Momentum Lecture

Momentum
Momentum is…
•Inertia in motion
•Mass x Velocity
Creating Momentum
•Greater Force =
Greater Momentum
Force creates acceleration, so pushing
harder makes you go faster.
Impulse is…
• Force applied x Time applied
• Change in Momentum
Therefore…
•Δ(mv) = Ft
Impulse is…
• Commonly confused with
impact (be careful)
• The force applied
• Determined by solving the
equation Ft  mv for force
Momentum
Increasing Momentum:
–Increase force or time
–Greatest momentum:
• Big force for big time
Momentum
Decreasing Momentum
–When you stop you lose all of your
momentum – impulse is same no
matter how you stop
–More time means less force
(haystack)
–Less time means more force (brick
wall)
A Picture is Worth a Thousand Words
Man moves back,
increasing time and
decreasing force
Man leans in,
decreasing time and
increasing force
Bouncing
• When something bounces the impulse
is greater because you bring velocity to
0 and then increase it the other way
A few more examples
• Conservation of momentum can also be shown
with moving objects that undergo a weight
change.
– The following examples show a freight train that has
weight added to it while it is moving – notice the
change in velocity that occur with the weight
increase
• Are mass and velocity proportional or inversely
proportional?
Big Cart, Little Brick
Little Cart, Big Brick
The Fish Example Part #1
The Fish Example Part #2
Conservation in Collisions
• Net Momentum Before =
Net Momentum After
– Friction is usually considered to be
negligible during the collision itself
Collision Types
–Elastic collisions objects are not
deformed or attached and don’t
generate heat or sound.
–Inelastic collisions colliding objects
become tangled or coupled together.
They still follow the law of conservation,
but after the collision they are attached
to each other.
Inelastic Collision Example #1
This demonstration illustrates an astronaut in a
frictionless environment undergoing an inelastic
collision with another astronaut
Inelastic Collision Example #2
Inelastic Collision Example #3
Inelastic Collision Example #4
Inelastic Collision Example #5
Elastic Collision Example #1
Elastic Collision Example #2
Elastic Collision Example #3
Look at the difference…
Look at the difference…
Look at the difference…
Momentum Vectors
 Momentum vectors combine like all other
vectors.
 When looking at the vectors involved in a
collision the vector(s) before and after the
collision must have the same resultant.
Vector Collision Example