Ch. 9 Study Guide- Physics

Be able to identify any factor(s) that could have affected your results from the momentum and collision lab.

Factors include- friction, timing, construction error, tables (not leveled), calculation error

impulse formula

FΔt

equation from mini-quiz

FΔt= mΔv

impulse-momentum theorem

FΔt= pf-pi

list four vectors

force, velocity, momentum, impulse

angular momentum unit

kg m^2/s

momentum formula

p=mv (mass x velocity)

vector definition

quantities, such as position, that have both magnitude and direction

angular velocity

the angular displacement of an object divided by the time needed to make the displacement

variables from angular momentum equations

F= force Δt= time interval m= mass v= velocity L= angular momentum w= angular velocity I= inertia p= momentum

List 2 ways to create a large impulse.

1. large force acting over a short period of time 2. smaller force acting over a long period of time

impulse unit

N x sec

Newton's second law of motion states that if no net force is exerted on a system, no acceleration is possible. Does it follow that no change in momentum can occur.

No net force on the system means no net impulse on the system and no net change in momentum. However, individual parts of the system may have a change in momentum as long as the net change in momentum is zero.

A 0.11-g bullet leaves a pistol at 323 m/s while a similar bullet leaves a rifle at 396 m/s. Explain the difference in exit speeds of the two bullets, assuming that the forces exerted on the bullets by the expanding gases have the same magnitude.

The bullet is in the rifle a longer time, so the momentum it gains is larger.

Explain what happened to the momentum of the metal ball, from the collision lab, when it was allowed to roll down without any obstruction.

The momentum increased.

Explain what occurred to the momentum when there was a collision on the track.

We lost momentum, but it should have been conserved.

Can a bullet have the same momentum as a truck?

Yes, for a bullet to have the same momentum as a truck, it must have a higher velocity because the two masses are not the same.

Is it possible for an object to obtain a larger impulse from a smaller force than it does from a larger force?

Yes, if the smaller force acts for a long enough time, it can provide a larger impulse.

You are sitting at a baseball game when a foul ball comes in your direction. You prepare to catch it bare-handed. To catch it safely, should you move your hands toward the ball, hold them still, or move them in the same direction as the moving ball?

You should move your hands in the same direction the ball is traveling to increase the time of the collision, thereby reducing the force.

torque

a measure of how effectively a force causes rotation; is equal to the force times the lever arm

coordinate system

a system used to describe motion that gives the zero point location of the variable being studied and the direction in which the values of the variable increase

A pitcher throws a curve ball to the catcher. Assume that the speed of the ball doesn't change in flight. a) Which player exerts the larger impulse on the ball? b) Which player exerts the larger force on the ball?

a) The pitcher and the catcher exert the same amount of impulse on the ball, but the two impulses are in opposite directions. b) The catcher exerts the larger force on the ball because the time interval over which the force is exerted is small.

An ice skater is doing a spin. a) How can the skater's angular momentum be changed? b) How can the skater's angular velocity be changed without changing the angular momentum?

a) by applying an external torque b) by changing the momentum of inertia

impulse

the net force on an object over time period force is applied

angular momentum

the product of a rotating object's moment of inertia and its angular velocity; measured in kg x m^2/s

momentum

the product of the object's mass and the object's velocity; is measured in kg x m/s

inertia

the tendency of an object to resist change