Physics Unit 10 Review

Angular displacement

The angle of the movement of a body in a circular path

Angular speed

The rate of change of angular displacement

Angular acceleration

The time rate of change of angular velocity

Torque

The measure of the force that can cause an object to rotate about an axis

Force

The push or pull on an object with mass causes it to change its velocity.

Linear acceleration

The uniform acceleration caused by a moving body in a straight line

Balanced forces

Forces that are equal in magnitude but opposite in direction

Balanced torques

The size and direction of the torques acting on an object are exactly balanced

Axis of rotation

The straight line through all fixed points of a rotating rigid body around which all other points of the body move in circles

Center of gravity

The average location of the weight of an object

Rotational mass

A description of how easy or difficult it is to rotate a body or to stop it once it is rotating

Mass

The measure of the amount of matter in an object

Parallel forces

Forces that lie in the same plane and have lines of action that never intersect each other

Law of conservation of angular momentum

When angular momentum is conserved when there is zero net torque applied to a system, where the system is the object or objects that are rotating

Gyroscope

A device used for measuring or maintaining orientation and angular velocity

Precession

The change in orientation of the rotational axis of a rotating body

Topple

To fall because of overbalance

Stability

The ability of an object to maintain its balance after being disturbed

1st and 2nd condition of equilibrium

Firstly, the net force acting upon the object must be zero. Secondly, the net torque acting upon the object must also be zero

Rotational inertia

A property of any object which can be rotated

Moment of inertia

Quantitative measure of the rotational inertia of a body

Forces make objects accelerate in a straight line (linearly) torques make objects ___?___.

accelerate angularly (increase rotational speed)

An angle of ___?___ between the force and the lever arm gives a maximum torque.

90 degrees

Torque is calculated by ___?___ the ___?___ with the ___?___ as described in the equation ___?___.

multiplying, force, lever-arm, T = F x  l

Torque can have a direction of ___?___ or ___?___.

clockwise, counterclockwise

An object like a seesaw is balanced when ___?___ and ___?___ are balanced.

forces, torques

C.O.G. is the abbreviation for ___?___.

center of gravity

Two objects whose c.o.g. is located where no material exists are ___?___ .

answers will vary (boomerang, hoop)

An object will topple if its c.o.g is located outside of its ___?___.

base

An object is most stable when its ___?___ is located at the ___?___ possible point.

cog, lowest

You can increase your bodies stability by moving your feet ___?___.

apart

An object at rest stays at rest and an object in motion stays in motion describes the property of matter  called ___?___.

inertia

Objects that are rotating have ___?___ inertia.

rotational

If the mass of a body is located close to its axis of rotation, it is ___?___ to rotate the body because it  has a ___?___ rotational mass.

easy, low

A ___?___ pendulum is more difficult to rotate and therefore swings more slowly.

long

Animals with shorter legs have ___?___ strides than long-legged animals because their legs have  ___?___ rotational masses.

quicker, less

The formula for angular momentum is ___?___.

L = Iω

If you are rotating on an office chair with your arms and legs extended and you pull them inward your:

a. Rotational speed will ___?___ 

b. Angular momentum will ___?___ 

c. Rotational mass will ___?___ 

d. Angular acceleration will ___?___

a. Increase 

b. Stay the same

c. Decrease 

d. Increase

A gymnast tucks to make a somersault. Her rotational mass decreases during the tuck. Her ___?___ is  conserved because her ___?___ increases during the tuck.

angular momentum, rotational speed

The angular momentum before a somersault is equal to the ___?___ after the somersault.

angular momentum

A spinning bicycle wheel does not easily fall over because it behaves like a ___?___ which has the  characteristic of always keeping its axis pointed in the same direction.

gyroscope

The symbols that represent angular distance, angular speed, and angular acceleration respectively  are ___?___, ___?___, & ___?___.

Δ, θ, ω, α

When a rotating body increases angular speed, it is said to be undergoing ___?___.

angular acceleration

Torque is the ___?___ effect of a force about an axis.

twisting

Torque is found by the product of ___?___ and ___?___.

force, lever-arm

Two ways of increasing torque are ___?___ force or ___?___ the lever arm.

increasing, increasing

The point that a rotating body spins about is called ___?___.

axis of rotation

The point where all mass of a body may be considered to be concentrated is its ___?___.

cog

List three characteristics of the center of gravity.

a. not always within the object 

b. always tries to reach the lowest  possible position 

c. natural axis of rotation

The stability of an object can be increased by ___?___ the cog or by ___?___ its base.

lowering, widening

When the mass is concentrated far from the axis of rotation, the body has ___?___ rotational mass.

high

The angular acceleration will increase if the torque applied to a rotating body ___?___ or if the  rotational mass of the body ___?___.

increases, decreases

When a skater increases her rotational mass, her angular speed ___?___ to conserve angular  momentum.

decreases

A body rotating about an axis is called a ___?___.

gyroscope

___?___ occurs when a force tries to change the direction of the ___?___ of rotation of the gyroscope.

Precession, axis

How far can a body be tipped before it topples over?

Until the cog is outside of the base or support of the object.

Why doesn’t the Leaning Tower of Pisa topple over?

Its cog is within its base.

Why must you bend forward when carrying a heavy load in your backpack?

The backpack shifts your cog outside of your heels so you bend forward to shift it back over your feet (base).

Why is it easier to carry the same amount of water in two buckets, one in each hand, than in a  single bucket?

It is the same weight but the torque is harder to balance with only one bucket compared to two.

How can three bricks be stacked so that the top brick has maximum horizontal displacement from  the base of the bottom brick?

First brick out a ¼, second brick out ½.

Nobody at the playground wants to play with the obnoxious boy, so he fashions a seesaw out of a  plank of wood and a rock that he can play with by himself. Explain how this can be done. 7. One 50 gram rock is balanced on a meter-stick with a fulcrum at 25 cm. The rock is at the 0 cm  mark. What is the mass of the meter-stick?

He can balance the torques using the weight of the bar instead of another child. He must put the  bar off-center for this to be possible.