2Energy = ability to produce a change in itself or its surroundings. Work transfer energy by mechanical means.Kinetic energy = energy of motionKe = ½ mv2Work-Energy Theorem K = W
3WorkProduct of force and distance; scalar quantity. W = FdUnit is J named after James Prescott Joule.1 J = 1 N*mWork is done only if object moves in the direction of the applied force.Ex Prob 226 Prac Pr 227
4Work and Direction of Force Figure 10-4 p 227 shows work can be broken into its components and that work is done only in the component in which the force is applied.
5W = Fd cos Since cos 90 = 0, no work is done in the vertical direction.Work done by the friction of grass is negative.Positive work done by you and means you are working.
6Ex Prob 228 Pr Prob 229On a Force vs Displacement Graph, the area under the curve is work. FigPower = rate of doing workP = W/t
7Measured in watts (W)1W = 1 J/sOften measured in kW because 1 W is so small.Ex Prob 230 Prac Pr 231
810.2 MachinesEases load by changing magnitude or direction of force, but it does not change the amount of work done.Figure Example of Simple Machines
9Simple and Complex Machines Work you do = WiWork machine does = Wo
10Effort force, Fe - force you exert on machine Resistance force, Fr - force exerted by machineMechanical Adv = Fr / FeA machine can increase force, but not energy.