2 Energy = 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
3 WorkProduct 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
4 Work 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.
5 W = 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.
6 Ex Prob 228 Pr Prob 229On a Force vs Displacement Graph, the area under the curve is work. FigPower = rate of doing workP = W/t
7 Measured in watts (W)1W = 1 J/sOften measured in kW because 1 W is so small.Ex Prob 230 Prac Pr 231
8 10.2 MachinesEases load by changing magnitude or direction of force, but it does not change the amount of work done.Figure Example of Simple Machines
9 Simple and Complex Machines Work you do = WiWork machine does = Wo
10 Effort force, Fe - force you exert on machine Resistance force, Fr - force exerted by machineMechanical Adv = Fr / FeA machine can increase force, but not energy.