Transcript PHYS 2_25_2013 notes

Notes: Monday, February 25,
2013
Title: Momentum and Impulse
EQ: Why do gymnasts use floor mats
that are very thick?
Momentum
• Momentum = mass × velocity
• The letter we use to say momentum is p
• So another way of writing the equation
p=mv
• A moving object can have a large momentum
if it has a large mass, high speed, or both.
Applied Question
• When would a roller skate and a truck have
the same momentum?
Impulse
• An impulse is a change in momentum and
depends on the force applied and the length
of time it acts.
• Or impulse = force × time
• Impulse = change in momentum
Ft=∆mv
» Remember ∆ means change in
Changes in Momentum
Increasing Momentum
• To increase momentum the
most you want to apply the
greatest possible force for
the longest possible time
• Baseball players do this by
swinging as hard as possible
and by following through.
Decreasing Momentum
• To decrease momentum
without causing damage the
best way is use less force
over an extended amount
of time.
• When padding is used
collisions happen over
longer time, such that the
change in momentum cause
less damage.
Applied Question
• When a dish falls, will the impulse be less if it
lands on a carpet than if it lands on a hard
floor?
Bouncing
• The impulse required to bring an object to a
stop and then throw it back again is greater
than the impulse required merely to bring the
object to a stop.
Happy Sad Physics Spheres
Concept Checking Questions
• A lunar vehicle is tested
on Earth at a speed of
10 [km/h]. When it
travels as fast on the
moon, is its momentum
more, less, or the
same?
• When you ride a bicycle
at full speed and the
bike stops suddenly,
why do you have to
push hard on the
handlebars to keep
from flying forward.
Concept Checking Questions
• What does an airbag do
to help you reduce
damage to your head in
a car accident?
• When jumping from a
significant height, why
is it advantageous to
land with your knees
slightly bent?