According to Physics

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According to Physics
Work
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According to physics, work is
The transfer of energy to a body by the
application of a force that causes the body to
move in a direction parallel to the force.
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In other words

• If a force (F) is applied to an object in the
  same direction as the change in position of the
  object (?x), then the force does positive work on
  the object.

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The work done by the force can be calculated by
using the formula
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For example

• A boy pushes a box 3.0 m across a smooth marble
  floor. If the boy pushes with a force of 10 N
  parallel to the floor how much work does he do on
  the box?

F
?x
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Given
Calculate
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Another possibility is
If a force (F) is applied to an object in the
opposite direction from the change in position of
the object (?x), then the force does negative
work on the object.
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For example
?x
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In this problem the force and change in position
are in opposite directions so we need to decide
which direction is positive and which negative.
Lets say that North is to the right and positive.
This means that the force will be negative and
the change in position is positive. Make note of
this in your diagram.
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Given
Calculate
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Question

• What happens if the force is perpendicular to the
  change in position of the object?

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Answer

• No work is done by that force on the object.

Work
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For example

• A 350 N rock rests on top of a box as the box
  slides across a smooth floor through a distance
  of 10 m. How much work is done on the box by the
  weight of the rock?

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• The answer is of course 0 J. This is due to the
  fact that the weight of the rock cannot
  accelerate the box along a horizontal surface.

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Another Question

• What if the force isnt parallel OR
  perpendicular? What if instead the force is at
  an angle with respect to the change in position?

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Recall from our discussion of vectors and forces

• A force acting at an angle can be said to be
  acting in two dimensions at the same time.

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• For work problems you would break the force down
  into a component parallel to the change in
  position ( ).

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• And a component perpendicular to the change in
  position ( ).

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• Only the component of the force that is parallel
  to the change in position can be used to find the
  work done on the object

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• Only the component of the force that is parallel
  to the change in position can be used to find the
  work done on the object

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• Only the component of the force that is parallel
  to the change in position can be used to find the
  work done on the object

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• Only the component of the force that is parallel
  to the change in position can be used to find the
  work done on the object

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For example

• A man pushing a lawn mower pushes straight along
  the handle

F
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• Only the component of the force parallel to the
  change in position does any work.

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This is why
We use the subscript on the force. It helps us
remember that only forces on an object that are
parallel to the change in position of the object
do any work.