Work, Energy

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Work, Energy Power
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There are many different TYPES of Energy.

• Energy is expressed in JOULES (J)
• 4.19 J 1 calorie
• Energy can be expressed more specifically by
  using the term WORK(W)

Work The Scalar Dot Product between Force and
Displacement. So that means if you apply a force
on an object and it covers a displacement you
have supplied ENERGY or done WORK on that object.
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Scalar Dot Product?

• A product is obviously a result of multiplying 2
  numbers. A scalar is a quantity with NO
  DIRECTION. So basically Work is found by
  multiplying the Force times the displacement and
  result is ENERGY, which has no direction
  associated with it.

Thie means that F and x MUST be parallel. To
ensure that they are parallel we add the cosine
on the end where the cosine is the angle between
the direction of the force and the direction of
the displacement. If the force and displacement
are parallel, the angle is zero, and the cosine
is one.
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Work
The VERTICAL component of the force DOES NOT cause the block to move the right. The energy imparted to the box is evident by its motion to the right. Therefore ONLY the HORIZONTAL COMPONENT of the force actually creates energy or WORK.
When the FORCE and DISPLACEMENT are in the SAME DIRECTION you get a POSITIVE WORK VALUE. The ANGLE between the force and displacement is ZERO degrees.
When the FORCE and DISPLACEMENT are in the OPPOSITE direction, yet still on the same axis, you get a NEGATIVE WORK VALUE. This negative doesn't mean the direction!!!!
When the FORCE and DISPLACEMENT are PERPENDICULAR, you get NO WORK!!! The ANGLE between the force and displacement in this case is 90 degrees.
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The Work Energy Theorem

• Up to this point we have learned Kinematics and
  Newton's Laws. Let 's see what happens when we
  apply BOTH to our new formula for WORK!

• We will start by applying Newton's second law!
• Using the v2 equation !
• An interesting term appears called KINETIC
  ENERGY or the ENERGY OF MOTION!

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The Work Energy Theorem

• And so what we really have is called the
  WORK-ENERGY THEOREM. It basically means that if
  we impart work to an object it will undergo a
  CHANGE in speed and thus a change in KINETIC
  ENERGY. Since both WORK and KINETIC ENERGY are
  expressed in JOULES, they are EQUIVALENT TERMS!

" The net WORK done on an object is equal to the
change in kinetic energy of the object."
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Example WFxcosq

• A 70 kg base-runner begins to slide into second
  base when moving at a speed of 4.0 m/s. The
  coefficient of kinetic friction between his
  clothes and the earth is 0.70. He slides so that
  his speed is zero just as he reaches the base (a)
  How much energy is lost due to friction acting on
  the runner? (b) How far does he slide?

-560 J
480.2 N
1.17 m
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Work Done By Friction

• The frictional force of a surface always acts in
  the opposite direction of an objects
  displacement. This means that friction will
  always do negative work on an object. An object
  will always do positive work on the surface

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Work Energy

• A child pulls a 5kg sled with a rope angled 37
  degrees above the horizontal with a force of 10N.
  The coefficient of friction is 0.1 How much work
  does he do? Friction? How fast will the sled be
  moving after moving 4meters?

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Work Energy

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Work Energy

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Work Energy

• How much work is done by gravity?
• How much work is done by the normal force?

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Work as the transfer of energy

• Just as there is conservation of mass in the
  universe. There is also a conservation of energy.
  
• Energy is neither created or destroyed
• Energy is transferred from one object to another
  or changes from one form to another
• The change in an objects kinetic energy is the
  result of the net work done on it.
• Energy Gained is positive work
• Energy lost is negative work

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The Scalar Nature of Energy

• Energy is a scalar quantity. It does not have
  direction. An object in motion only has positive
  kinetic energy due to the equation using v2
• For work-energy calculations, only the speed of
  an object can be calculated, not its velocity

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Work Done by Gravity

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In this case, because the object is at rest
initially, the change in kinetic energy is equal
to the final kinetic energy
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Solve for the final velocity of an object after
being dropped from height h

• Work-Energy

• Kinematics

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Potential Energy

• An object with kinetic energy can do work on
  another object.
• An object that can fall has the ability to do
  work once it has fallen.
• This energy by virtue of its position is its
  potential energy.

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Potential Energy Requires a Reference Level
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Potential Energy Due to Gravity

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