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Conservative

Force of gravity

What is the key distinction between the two?

-when a conservative force acts, the work it does is stored in the form of energy that can be released at a later time

gravity

(physics) the force of attraction between all masses in the universe

Kinetic Friction

Friction between moving surfaces

recovered later as kinetic energy

The work done be a nonconservative force cannot be...?

Instead, what occurs?

the work of a nonconservative force is converted to other forms of energy

zero total work

How much work does a conservative force do on a closed path?

Potential Energy

(mass) x (g) x (height)

kinetic energy

a running dog

a storage system for energy

In a sense, what is potential energy?

no

nitrogen monoxide

Instead, what happens to the energy?

it is dissipated into other forms of energy such as heat or sound

yes

Is velocity a vector?

conservative forces

As such, only what type of foces have the potential energy storage system?

-trick question!

What expression describes potential energy?

Why not?

because each different conservative force has a different expression for potential energy

potential energy decreases

When an object falls, what is the impact of the fall on potential energy?

potential energy increases

When an object is lifted, what is the impact of the fall on potential energy?

Joules

Potential energy is measured in units of_______.

scalar

a physical quantity that has magnitude but no direction

energy cannot be created or destroyed

What does the energy conservation theorem state?

positive work removes PE and transforms it into KE

In terms of PE and KE, what does positive work do?

negative work removes KE and transforms it into PE

In terms of PE and KE, what does negative work do?

As such, what is a new definition of work that we can employ?

work is the process of energy transfer from one form of energy to another

What specifically is gravitational PE?

stored energy an object has due to being under the gravitational influence of another body

PEg = mgh

What is the equation that describes the relationship between PEg and work?

we are free to choose

What is h set to when using this equation?

What is usually the best choice?

to set H to zero at the lowest height of interest

KE = 0 for balls A and B

You are given one ball (A) that is dropped from a low height and one ball (B) that is dropped from a high height. What is KE equal to for balls A and B prior to release?

PE b initial > PE a initial

What is the relationship between the PEs of balls A and B?

Why?

because both person a and B cover the same angle in the same time

positive work

As A and B are released and fall towards the ground, what type of work does gravity do?

What does gravity do interms of PE and KE?

Gravity takes energy from PE storage and puts it into KE

all of the energy has moved from potential energy to kinetic enervy

By the time the object has reached the bottom, where is all of the energy?

Which object has more KE at the end of the motion? Why?

ball B has more KE at the end of the motion because object B had more PE to begin with

Which object then has a greater velocity? Why?

ball B has a greater velocity because it has a greater KE

the ability to calculate time

What is the only thing that we give up when we use the energy method?

What is the definition of mechanical energy?

the sum of potential and kinetic energies of an object

mechanical energy is conserved

What happens to mechanical energy in systems involving only conservate forces?

no it does not

If a force does zero net work, does it need to be accounted for when performing calculations using the energy method?

KE decreases

When gravity does negative work on a rising object, what is the impact on KE?

KE increases

When gravity does positive work on a falling object, what is the impact on KE?

What is mechanical energy?

the sum of the potential and kinetic energies of an object

mechanical forces Change the amount of mechanical energy in a system

What impact do nonconservative forces have on the amount of mechanical energy in a system?

Provide an example

nonconservative forces might decrease mechanical energy by converting it into thermal energy

increases the total mechanical energy of a system

What impact does positive nonconservative work have on a system?

Ei < Ef

Therefore, what is the relationship between Ei and Ef?

decreases the total mechanical energy of a system

What impact does negative nonconservative work have on a system?

What impact does zero nonconservative work have on a system?

has no impact on the total mechanical energy of a system

Ei + Wnc = Ef

What is the final definition of the energy method?

Is it possible for the kinetic energy of an object to be negative? Explain.

-the kinetic energy cannot be negative, since KE is given by 1/2mv^2 and m and v^2 are always positive or zero

Is it possible for the gravitational PE of an object to be negative? Explain

the gravitational PE can be negative since any level can be chosen to be zero

If the force on an object is zero, does that mean that the PE of the system is zero?

zero force implies that the rate of Change in the PE with distance is zero--that is the PE is constant--but the value of the PE can be anything at all

If the potential energy of a system is zero, is the force zero?

-similarly, if the PE is zero, it does not mean that the force is zero

-the change in gravitational potential energy for ball 1 is equal to the change for ball 2

Ball 1 is thrown to the ground; ball 2 is dropped to the ground from rest. Assuming the balls have the same mass and are released from the same height, how does the chang…

no nonconservative work is done on the bicycle

You coast up a hill on a bicycle with decreasing speed. Your friend pedals up the hill with constant speed. Ignoring friction, does the mechanical energy of your system (you-bike-Eart) increase, decrease, or stay the same?

Does the mechanical energy of your friend's system increase, decrease or stay the same?

your friend does positive nonconservative work to maintain a constant speed while going uphill

-as the leaf falls, air resistance exerts a force on it opposite to its direction

A leaf falls to the ground with a constant speed. Is KEi + PEi greater than, less than, or the same as KEf + PEf?

ME decreases

A block of mass M1 is connected to a second block of M2. When the blocks are released from rest, they move through a distance d at which point M2 hits the floor. As b…

the tension does negative nonconservative work

Is the nonconservative work done on block to by the tension in the rope positive, negative, or zero? Why?