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Ideas about Work
and Energy
What exactly is energy?
 We use this word in many different
 In physics, Work means something very
 Work = Force x distance where both
Force and distance are vectors.
 Work = the amount of Force applied
along the direction the object is moving.
 Work = Force x distance (mathematically
this is the dot product)
 Work can be positive or negative.
 Positive work increases the energy of an
 Negative work decreases the energy of
an object (think of friction on a sliding
Types of energy
 There are many types of energy………chemical,
nucular, sound, heat, etc.
 For now we will mainly be talking about mechanical
forms of energy which include Kinetic Energy, Potential
Energy, and spring energy
 Energy is often described as the ability to do work. It’s
a method of keeping track of “stuff” because in a
closed system energy is conserved.
 Conservation of Energy: one of the main conservation
laws in science.
Types of Mechanical
 Kinetic energy = ½ m v2 . This is the
energy an object has because it is
 Potential Energy (gravitational) = mgh.
This is the energy an object has because
it has height and the potential to fall.
Conservative Forces
 The Potential Energy of gravity is a
“conservative” form of energy.
 PE is path independent, it only depends
on the starting and ending locations.
 PE is always a change in energy,
meaning it has a reference point. This
reference point is the location you are
calling h = 0.
Conservation of Energy
 If no external forces are acting, then the total
energy of a system does not change.
 Examples of this are a 1)pendulum with no
friction or air resistance 2) roller coaster with
no friction or air resistance.
 Can determine speeds and heights based on
total energy remaining constant.
Energy problems with
 If an external force is acting, then Work is
done by this force.
 Work can either increase the starting
energy or decrease it.