# Work and Energy (G481)

Work and Energy mindmap, the first half of Module 3:

• Work
• Power
• Potential energy
• Kinetic energy
• Conservation of energy
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• Created by: Anna
• Created on: 08-04-13 12:51
• Work and Energy
• Work and Power
• Work done is the "product of the force and the distance moved by the force in the direction of travel"
• W=Fx
• F measured in Newtons (N)
• W measured in Joules (J)
• x is measured in meters (m)
• Remember to convert from cm/km/mm etc
• W=Fxcos?
• You can use a force triangle to work out these kinds of questions
• This is because it must be the distance moved IN THE DIRECTION OF THE FORCE
• Work done = Energy transferred
• E.g. moving a  book from a low shelf to higher one increases it's GPE but it had some to begin with so work done is the increase in GPE NOT the total
• Power is the "rate at which energy is transferred or the rate at which work is done
• P=W/t
• P is measured in Watts (W)
• "Watt is the unit of Power"
• W is work done - do not confuse with Watts (W)!
• t measured in s
• P=Fv
• W = Fx so P = Fx/t and v=x/t hence P = Fv
• Conservation of Energy
• "Energy cannot be created or destroyed. Energy can be transferred from one form to another but the total amount of energy in a closed system will not change."
• Because of this the kinetic energy transferred to gravitational must be equal and the other way around
• GPE = KE
• 1/2mv^2=mgh
• m's cancel out
• 1/2v^2=gh
• v^2=2gh
• KE = 1/2mv^2
• KE measured in Joules (J)
• m measured in kilograms (Kg)
• v measure in meters per second (ms^-1)
• Kinetic Engery
• Kinetic Energy is the "energy of an object due to its motion"
• KE = 1/2mv^2
• KE measured in Joules (J)
• m measured in kilograms (Kg)
• v measure in meters per second (ms^-1)
• Potential Energy
• elastic potential energy
• Energy stored in an extended or compressed material
• E = 1/2 ke^2
• e is the extension and is measured in m
• k is the stiffness constant
• E is  measured in Joules (J)
• gravitational potential energy
• "Energy stored by an object by virtue of its position in the Earth's gravitational field."
• GPE = mgh
• GPE measured in Joules (J)
• The Joule is defined by the work done when 1N moves an object by 1m which can be seen by looking at the units of equations. Here we have a mass, an acceleration and distance. F=ma so we have the equivalent.
• g measured in ms^-2 (acceleration due to gravity/ free fall and is = 9.81)
• The Joule is defined by the work done when 1N moves an object by 1m which can be seen by looking at the units of equations. Here we have a mass, an acceleration and distance. F=ma so we have the equivalent.
• these can be combined, see "conservation of energy.