# Energy 2

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Published on March 7, 2008

Author: zglazenburg

Source: slideshare.net

ENERGY By

Work Formula: Work= Force * Distance W=FD

Formula:

Work= Force * Distance

W=FD

Example of Work Lifting a load against Earth’s gravitational pull For example, this man is attempting to lift a box off of the ground against the pull of gravity.

Lifting a load against Earth’s gravitational pull

For example, this man is attempting to lift a box off of the ground against the pull of gravity.

Continued The heavier the load and the higher we lift the object, the more work we do. Superman here is doing quite the amount of work because he is lifting a very heavy mass, while at the same time lifting it high into the air.

The heavier the load and the higher we lift the object, the more work we do.

Superman here is doing quite the amount of work because he is lifting a very heavy mass, while at the same time lifting it high into the air.

Example 2 Weight lifting Work is done when lifting a barbell. The higher the mass, and the higher the barbell is lifted, the more work is done.

Weight lifting

Work is done when lifting a barbell. The higher the mass, and the higher the barbell is lifted, the more work is done.

Hold up Contrary to the past two slides, though the amount of work done depends on the displacement and the mass of the object, if a object is standing still, no work is being done

Contrary to the past two slides, though the amount of work done depends on the displacement and the mass of the object, if a object is standing still, no work is being done

Explanation Ok lets go back to superman, when he lifted the car above his head, he did a tremendous amount of work. However, now that the car is being held idly above his head, he is doing zero work.

Ok lets go back to superman, when he lifted the car above his head, he did a tremendous amount of work. However, now that the car is being held idly above his head, he is doing zero work.

Categories Work is generally separated into two different categories

Work is generally separated into two different categories

1 Work done against another force For example: an archer stretching his bow and arrow

Work done against another force

For example: an archer stretching his bow and arrow

2 Work done to change the speed of an object Example: bringing a car in motion to a stop.

Work done to change the speed of an object

Example: bringing a car in motion to a stop.

Unit of Measurement Joule 1 Newton exerted over 1 meter That guy is James Joule, the guy the unit is named after

Joule

1 Newton exerted over 1 meter

That guy is James Joule, the guy the unit is named after

Sample Question How much work is done on a 100N boulder that you carry horizontally across a 10m room? CLICK FOR ANSWER

How much work is done on a 100N boulder that you carry horizontally across a 10m room?

Power Formula: Power = Work divided by Time P=W/t

Formula:

Power = Work divided by Time

P=W/t

Power Power is the measure of how long it takes you to do work. Example: How long it takes to run up a flight of stairs

Power is the measure of how long it takes you to do work.

Example: How long it takes to run up a flight of stairs

Unit of Measurement Watts 1 Joule in 1 sec That’s James Watt

Watts

1 Joule in 1 sec

That’s James Watt

Sample Question What power is expanded if you lift a 100N boulder a distance of 1 m in a time of 1 s CLICK FOR ANSWER

What power is expanded if you lift a 100N boulder a distance of 1 m in a time of 1 s

Types of Energy

Mechanical Mechanical energy is the energy due to the position of something, or the movement of something There are two types of mechanical energy

Mechanical energy is the energy due to the position of something, or the movement of something

There are two types of mechanical energy

Potential Energy Potential energy is stored energy in an object. Formula: PE=mgh Example: in a stretched rubber-band, energy is stored in the rubber band then used when released.

Potential energy is stored energy in an object.

Formula: PE=mgh

Example: in a stretched rubber-band, energy is stored in the rubber band then used when released.

Kinetic Energy Kinetic energy is energy used in motion. Formula: 1/2(m)(v)(v) Example: A runner is expanding kinetic energy.

Kinetic energy is energy used in motion.

Formula: 1/2(m)(v)(v)

Example: A runner is expanding kinetic energy.

Sample Question When the brakes of a motorcycle traveling at 60km/h become locked, how much further than the motorcycle skid than if it travels at 20km/h? CLICK FOR ANSWER

When the brakes of a motorcycle traveling at 60km/h become locked, how much further than the motorcycle skid than if it travels at 20km/h?

Law of Conservation of Energy Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes

Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes

Efficiency Useful work output Total work input That fraction will always be less than one.

Useful work output

Total work input

That fraction will always be less than one.

Answer Power= 100J/1s=100W 100 Watts CLICK TO GO BACK TO PREVIOUS SLIDE

Power= 100J/1s=100W

100 Watts

CLICK TO GO BACK TO PREVIOUS SLIDE

Answer 2 You do not work on the boulder moved horizontally, because you apply no force (except for the tiny bit to start and stop it) in its direction of motion. CLICK TO GO BACK

You do not work on the boulder moved horizontally, because you apply no force (except for the tiny bit to start and stop it) in its direction of motion.

CLICK TO GO BACK

Answer 3 Nine times farther; the motorcycle has nine times as much kinetic energy when it travels three times as fast. CLICK TO GO BACK

Nine times farther; the motorcycle has nine times as much kinetic energy when it travels three times as fast.

CLICK TO GO BACK

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