Transcript ImpulseandMomentum

Impulse and Momentum
Momentum
“The change of motion is ever proportional to the motive
force impressed; and is made in the direction of the right
[straight] line in which that force is impressed”
Sir Isaac Newton
What Newton called “motion” translates into “moving inertia”
Today the concept of moving inertia is called momentum
which is define as the product of mass and velocity
momentum mass  velocity
Momentum is a
vector quantity
p  mv
SI unit of momentum
1 kilogram  1
meter
kg m
=1
second
s
Impulse and Momentum
Newton’s 2nd Law was written in terms of momentum and force
p
F
t
mv
F
t
F  ma
Ft  mv
average or
constant force
impulse
momentum
change
Impulse causes a change of momentum for any object; this is
analogous to work causes a change of energy for any object
Impulse is a vector quantity
I  Ft
SI unit of impulse
1 newton 1 second =1 N s
1 N s = 1kgm / s
Impulse of Collisions
Momentum decreased by a small force over a long time
Momentum decreased by a large force over a short time
Impulse of Sports
A boxer who “rolls with the punch”
will experience less force
In what other sports should you extend
the impulse time for safety?
Impulse of Sports
In many sports you are taught to “follow through”. Why?
As you “follow through” the time of contact with the ball is
increased, so the amount of momentum change is also
increased. More momentum….more speed (and/or distance)!
Impulse of Sports
Impact
time
(ms)
Ball
Mass
(kg)
Speed
imparted
(m/s)
Baseball
0.149
39
1.25
Football (punt)
0.415
28
8
Golf ball (drive)
0.047
69
1
Handball (serve)
0.061
23
12.5
Soccer ball (kick)
0.425
26
8
Tennis ball (server)
0.058
51
4
Impulse of Sports
Example:
You pull out your 9 iron for a 150 yard approach shot to the
18th green at Augusta National. You apply an average force
of 3000 N to a 47 gram Titleist Professional golf ball, giving
it a speed of 75 m/s off the clubhead. How long is the club in
contact with the golf ball?

1 kg 
m  47 g 
  0.047 kg

1000 g 
Ft  mv  m(v f  vi )
3000 Nt  0.047 kg75 m / s - 0 
t  1.18  10 3 s  1.18 ms
Impulse of Spacecraft
Example:
On September 12, 1966, a Gemini spacecraft met and docked with
an orbiting Agena launch vehicle. NASA decided to determine the
mass of the Agena. While coupled Gemini's motor was fired,
exerting a constant thrust of 890 N for 7.0 s. As a result, the
Gemini-Agena sped up by 0.93 m/s. Assuming Gemini's mass is a
constant 3400 kg, calculate the mass of the Agena.
Ft  mv  m(v f  vi )
890 N7.0 s  3400 + mAG ENA 0.93 m / s
mAG ENA  3300 kg