Transcript Momentum and Impulse Notes

momentum = mass x velocity
p = mv
p = momentum; has units of kg*m/s
m = mass; has units of kg
v = velocity; has units of m/s
Momentum is a vector,
so direction is important.
An object’s momentum will change
if its mass and/or velocity
(speed and direction) changes.
According to Newton’s laws,
a net force causes an object to accelerate,
or change its velocity.
A net force, therefore, causes a
change in an object’s momentum.
More force is needed to quickly stop a
baseball thrown at 95 mph than to quickly stop
a baseball thrown at 45 mph, even though
they both have the same mass.
More force is needed to quickly stop a
train moving at 45 mph than to quickly
stop A car moving at 45 mph, even though
they both have the same speed.
Both mass and velocity are important
factors when considering the force
needed to change the motion of an object.
REMEMBER…
F = ma
(Newton’s Second Law)
The formula F = ma can broken
down into the following units:
N = (kg)(m/s2)
http://www.youtube.com/watch?v=C5h2NF2xMYI
Impulse = change in momentum
To have a change in momentum there must
be a force applied during a time interval
Change in Momentum
Symbols:
equation
p =m v
Units: Change in Momentum
p = (kg)(m/s)
Impulse equation
J = F t
Units: Impulse
J =
(N)(s)
Symbols:
p =m v
J = F t
Since Δ means “the change in” – we can
rewrite the equation on the left to be:
pf - pi = m(vf – vi)
Now we can combine the two equations into one:
mvf – mvi = F t
The impulse –
momentum theorem
states that the impulse on
an object is equal to the
change in momentum.
J = F∆t = m∆v = m(vf-vi)
The greatest change in
velocity will occur when
the impulse is the greatest.
By increasing the amount
of force and the amount of
time the force is applied,
the greatest change in
velocity can be achieved.
A 1000 kg car moving at 30 m/s (p = 30,000 kg*m/s)
can be stopped by
30,000 N of force acting for 1.0 s (a crash!)
or
by 3000 N of force acting for 10.0 s (normal stop)
http://www.youtube.com/watch?v=3vDQm0qIYi0
Practice Problem 1:
Tiger Woods hits a 0.1 kg golf ball,
giving it a speed of 76.1 m/s. What
impulse does he impart to the ball?
Practice Problem 2:
Wayne hits a station 0.2 kg hockey puck
with a force that lasts for 0.1 s and
makes the puck shoot across the ice
with a speed of 16.0 m/s scoring a goal
for the team. With what force did
Wayne hit the puck?