Presentation on theme: "Energy, Work, and Simple Machines Chapter 10. Energy = ability to produce a change in itself or its surroundings. Work transfer energy by mechanical means."— Presentation transcript:
Energy, Work, and Simple Machines Chapter 10
Energy = ability to produce a change in itself or its surroundings. Work transfer energy by mechanical means. Kinetic energy = energy of motion Ke = ½ mv 2 Work-Energy Theorem K = W
Work Product of force and distance; scalar quantity. W = Fd Unit is J named after James Prescott Joule. 1 J = 1 N*m Work is done only if object moves in the direction of the applied force. Ex Prob 226 Prac Pr 227
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.
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.
Ex Prob 228 Pr Prob 229 On a Force vs Displacement Graph, the area under the curve is work. Fig Power = rate of doing work P = W/t
Measured in watts (W) 1W = 1 J/s Often measured in kW because 1 W is so small. Ex Prob 230 Prac Pr 231
10.2 Machines Eases load by changing magnitude or direction of force, but it does not change the amount of work done. Figure Example of Simple MachinesFigure
Simple and Complex Machines Work you do = Wi Work machine does = Wo
Effort force, Fe - force you exert on machine Resistance force, Fr - force exerted by machine Mechanical Adv = Fr / Fe A machine can increase force, but not energy.