Work = Force x Distance:

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Calculating Work:

One can calculate the work done by an airplane by using the equation: W = F x D

For instance, if a model airplane exerts 0.25 Newtons over a distance of 10 meters, the plane will expend 2.5 Joules.

 

 

Work

= F x D

 

= 0.25 * 10

 

= 2.5 Joules

 

If you apply a force over a given distance - you have done work.  Work = Change in Energy. If an object’s kinetic energy or gravitational potential energy changes, then work is done. The force can act in the same direction of motion. Or, the force can act against the motion. (Drag and friction do that.) Forces can act when objects touch.

In general, the energy transferred depends on the amount of force and the distance over which that force is exerted.

If the man pushes the rock in the direction of the force, he has done work. If the rock rolls back and pushes him, then the rock does work on the man.

 

No work: If the net force is perpendicular to the motion then no work is done. If you push on an object and it doesn’t move, then no work is done.  If an object’s kinetic energy doesn’t change, then no work is done.

Another Equation for Calculating Work:

Work = Mass * Gravity * Height and is measured in Joules. Imagine you find a 2 -Kg book on the floor and lift it 0.75 meters and put it on a table. Remember, that “force” is simply a push or a pull.

Work

=

M

*

G

*

H

 

=

2

*

9.8

*

0.75

 

=

14.7

Joules

 

 

 

If you lift 100 kg of mass 1-meter, you will have done 980 Joules of work.

Work

=

M

*

G

*

H

 

=

100

*

9.8

*

1

 

=

980

Joules

 

 

 

 

 

While the book sits on the table, no work is being done because no object is moving, even though forces are involved. If a force (like gravity) is applied to an object (like the book) but it does not move, no work has been done.

 

Work

=

M

*

G

*

H

 

=

2

*

9.8

*

0

 

=

0

Joules

 

 

 

 

Which of the following will result in more work? Running straight up hill, or taking a zigzag path up the hill?

The work will be the same for both paths. The direct path requires more force, but less distance, while the zigzag path requires less force but more distance.

Work = Mass * Gravity * Height

The equation above shows how to calculate the work done. As you can see, your work will be the same – no matter which path you take - because your mass doesn’t change during the trip. Gravity doesn’t change. The final height is the same. Therefore, work is the same.

 

Imagine you open a door by pushing near the hinges. Now imagine you open the same door by pushing near the handle. Which will result in more work? Again, the work done is the same. As you push the door near the hinges, the force needed to move it is greater, but the distance traveled is less. Pushing near the handle, the force is less, but the distance traveled is greater.

 

Energy

Energy is defined as the ability to do work. If you can measure how much work an object does, or how much heat is exchanged, you can determine the amount of energy that is in a system.  Read this for more information. As with work, energy is also measured in Joules. Energy is not created nor destroyed according to the Law of Conservation of Energy. Energy only changes form. It is transformed from one kind of energy to another. In fact, the energy that makes your body work can be traced back to the sun. Solar energy is transformed to chemical energy in the plants. We get chemical energy from the plants and animals we eat.

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