Work and Energy Work done by a constant force Work-Energy Theorem and KE Gravitational Potential...
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CHAPTER 6 Work and Energy • Work done by a constant force • Work-Energy Theorem and KE • Gravitational Potential Energy • Conservative Forces vs Non- conservative Forces • Conservation of Mechanical Energy • Power
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Transcript of Work and Energy Work done by a constant force Work-Energy Theorem and KE Gravitational Potential...
CHAPTER 6Work and Energy
•Work done by a constant force•Work-Energy Theorem and KE•Gravitational Potential Energy•Conservative Forces vs Non-conservative Forces•Conservation of Mechanical Energy•Power
Work Done by a Constant Force
Work is a scalar product of force and displacement with a unit of N*m or Joules (J).
A joule is the work done by applying a force of one newton through a displacement of one meter.
For work to be done on an object, the force must have a component in the same direction as the displacement.
Ex: pg 187 #1, pg 188 # 1, 3
Work-Energy Theorem and KE
Energy is the ability to do work. When work is done, energy is transferred. Unit for energy is the same as for work,
Joule. ***The amount of work done on a system
is exactly equal to the change in energy of the system.
Kinetic Energy is the energy an object has b/c of its motion.
Work = ∆ KE = ½ mvf2 – ½ mvi
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Ex: pg 189 #13, 15
Gravitational Potential Energy
Potential Energy is energy a system has because of its position or configuration.
An example of a rubber band, you store energy in the rubber band as elastic potential energy as you stretch it.
Another example is when you lift an object up against gravity.
PE = g * m * h
Conservative vs Non-conservative Forces
A force is conservative if the work done by the force does not depend on the path taken between any two points.
Examples of conservative forces are the gravitational force and the spring force as they conserve energy during a round trip.
Nonconservative forces are those that the work done depends on the path taken. Friction is an example as a longer path will dissipate more heat energy.
Work done by NCF generally cannot be recovered as usable energy.
Ex: pg 190 #29, 33 pg 191 #51, 53
Conservation of Mechanical Energy When work is done the energy of the
system changes form but the TOTAL AMOUNT of energy stays the same. Total energy is conserved.
**Law of Conservation of Energy The sum of the kinetic and potential
energies of a system is called the total mechanical energy of the system.
During freefall examples we can follow:GPEtop + KE top = GPEbottom + Kebottom
EX: pg 190 #36, 41
Power
Work can be done slowly or quickly. Power is the rate at which work is done. Power = work / time The units for power are J/s or Watts (W). A 75- watt light bulb is using 75 joules of
energy each second. Ex: pg 192 # 63, 69
