Physics 211 S3 Philosophy

Front 1

Forces are not physical things we can see. They do not take up space or have mass. But,

Back 1

We can measure forces through their effects; their push and pull between bodies or between a body and it's environment.

Front 2

Conservative forces: If I put

c-forces relative to position:

Only c-forces can

Back 2

work in, I can get it back out.

conservative forces depend only on position, not the path it took to get there.

have potential energy.

Front 3

What is work?

Back 3

A measure of energy transfer that occurs when an object is moved over a distance by a force (at least part of which is applied in the direction of the displacement).

Front 4

We always speak of work done

Back 4

on a particular body by a specific force.

Front 5

The total work done on a body by a specific force is related to

But the total work is also related to

When a particle undergoes a displacement, it speeds up if

Back 5

the body's displacement (to changes in its position).

changes in the speed of the body!

Wtot > 0, slows down if Wtot < 0, and maintains the same speed if Wtot = 0

Front 6

Apply the work-energy theorem to the block in the last flash card. When Wtot is positive,

When Wtot is negative,

When Wtot =0,

Back 6

the kinetic energy increases (the final kinetic energy Kf is greater than the initial kinetic energy Ki)

The kinetic energy decreases (Kf is less than Ki) and the speed is less after the displacement.

The kinetic energy stays the same (Ki = Kf) and the speed is unchanged.

Front 7

Force is

Work is

Mechanical energy (_________________) is conserved if

Back 7

-the way we transfer energy from one thing to another.

-the amount of energy we transfer!

-(the sum of kinetic and potential energy) is conserved if there are no nc-forces doing work.

Front 8

Energy is what you can

While work is

Back 8

Possibly do at any moment.

What you actually do. It is stuff that has happened (or that will happen).

Front 9

Energy is a property of

Back 9

a property of matter and space, objects and fields. It can be transferred between objects and can also be converted in form.

Front 10

Energy can not be...

Back 10

Energy can not be felt or touched. It is not a physical object. It is a scalar quantity, something we use to understand the world around us.

It causes objects to move or change.

Front 11

Energy is the quantitative

Back 11

the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object. Energy is the ability to do work.

Front 12

What are the two basic forms of energy?

Back 12

Kinetic energy or potential energy.

Kinetic energy is the energy of an object possesses due to its motion.

Potential energy is the energy held by an object because of its position relative to other objects.

Front 13

Potential energy is the energy by virtue of an object's position relative to other objects. Potential energy is often associated with restoring forces such as a spring or the force of gravity. The action of stretching a spring or lifting a mass is performed by an external force that works against the force field of the potential. This work is stored in the force field, which is said to be stored as potential energy. If the external force is removed the force field acts on the body to perform the work as it moves the body back to the initial position, reducing the stretch of the spring or causing a body to fall.

Back 13

Forces derivable from a potentialare also called conservative forces. Thework done by a conservative force is where is the change in thepotential energy associated with the force. The negative sign provides theconvention that work done against a force field increases potential energy,while work done by the force field decreases potential energy.

More abstractly, potential energy isthe energy difference between the energy of an object in a given position andits energy at a reference position.

Front 14

Mechanical energy

Back 14

In physical sciences, mechanical energy is the sum of potential energy and kinetic energy. It is the energy associated with the motion and position of an object.

Front 15

Common types of potential energy include

Back 15

The gravitational potential energy of an object that depends on its mass and its distance from the center of mass of another object.

The elastic potential energy of an extended spring, and

the electric potential energy of an electric charge in an electric field.

Front 16

Potential energy is the

Back 16

The stored energy required to do work. It is the energy that is inactive for the moment, but has the potential to do work. It is the energy difference between the energy of an object in a given position and its energy at a reference position.

Front 17

Power is ______________________ - so power is the ________________, and total _______ used is _______________________________________.

Back 17

rate of use of energy -

derivative of energy-flow, and total energy used is the time-integral of power use.

Front 18

If you lose energy when you move an object from an initial position and back, then you know

Back 18

non-conservative forces acted and did work on the object, stealing energy.

Front 19

Informally, a conservative force can be thought of as a force that ___________ __________ ______.

Suppose a particle starts at point A, and there is a force F acting on it. Then the particle is moved around by other forces, and eventually ends up at A again. Though the particle may still be moving, at that instant when it passes point A again, it has traveled a closed path. If:

Back 19

conserves mechanical energy.

the net work done by F at this point is 0, then F passes the closed path test. Any force that passes the closed path test (for all possible closed paths) is classified as a conservative force.