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”

SI unit of momentumMomentum is avector quantity

Today the concept of moving inertia is called momentum which is define as the product of mass and velocity

Impulse and Momentum

Newton’s 2nd Law was written in terms of momentum and force

SI unit of impulseImpulse is a vector quantity

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

average or constant force

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)!

BallMass

(kg)

Speed imparted

(m/s)

Impact

time

(ms)

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

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?

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.