Momentum

•The Texas Rangers lost momentum at the end of the season.

•The Ravens gain momentum as the season goes on.•You hear these terms a lot.•A team or politician on the move is said to have

“momentum” and is tough to stop.

Physics:

•Momentum: mass in motion.•All objects have mass. If they’re moving, they have

momentum.

Equation (on reference page, too)

Momentum = mass x velocity

p = mvStandard metric unit: kg·m/s

• It’s a vector quantity.•The momentum vector is in the same direction as the

velocity vector.•What we deal with is more precisely called linear

momentum, since it is straight line motion.

Example 1

Rich Gossage set a fastball record by hurling a 0.14 kg baseball at a speed of 46.3 m/s (104 mi/h). What was the magnitude of the ball’s momentum as it left his hand?

Example 2

•A 0.149 kg baseball travelling at 28 m/s due south approaches a waiting batter. The ball is hit and momentarily crushed; it springs back, sailing away at 46 m/s due north. Determine the magnitude of its initial and final momenta and the change in its momentum.

•Force must be applied to stop an object in motion.•More momentum = harder to stop

•Newton’s Second Law of Motion: an unbalanced force causes acceleration.

Derive the equation a bit and you come up with another way to write his Second Law…

Impulse-Momentum Equation

F Δ t = Δ pF Δ t is known in physics as the impulse of the force.

Impulse = change in momentum

Think about it

•How do you catch a water balloon at a water balloon toss?

Real World Applications

•Air bags in automobiles increase the time of impact, thereby minimizing the force of impact.

•Football helmets do the same.• In boxing, you’ll often notice a boxer who knows

he’s about to get hit in the head relax his neck, allowing his head to move backwards on impact. It’s called riding the punch and it extends impact time.

•Following through on a swing in tennis/baseball increases the velocity.

Example 3

•On Sep 12, 1966, a Gemini spacecraft docked with an orbiting Agena launch vehicle. With plenty of fuel left, NASA decided to determine the mass of the Agena. While coupled, Gemini’s motor was fired, exerting a constant thrust of 890 N in a fixed direction for 7.0 s. As a result of the little nudge, the Gemini-Agena sped up by 0.93 m/s. Assuming Gemini’s mass as a constant 3400 kg, compute the mass of the Agena.