Chapter 13.1 – Work, Power, and Machines transfer of energy to an object by the application of a force that causes the object to move in the direction of the force found by multiplying the force by the distance over which the force is applied Work = force x distance W = F d units of joules (J) if an object does not move, no work is done, work = zero

Chapter 13.1 – Work, Power, and Machines An apple weighing 1 N falls a distance of 1 m. How much work is done on the apple by the force of gravity? A bicycle’s brakes apply 125 N of frictional force to the wheels as the bike moves 14.0 m. How much work do the brakes do?

Chapter 13.1 – Work, Power, and Machines rate at which work is one or energy is transformed Power = 𝑤𝑜𝑟𝑘 𝑡𝑖𝑚𝑒 P = 𝑊 𝑡 unit of power is watt (W)

Chapter 13.1 – Work, Power, and Machines While rowing across a lake, John does 4000 J of work on the oars in 60.0 s. What is his power output? Anna walks up the stairs on her way to class. She weighs 560 N and the stairs go up 3.25 m vertically. If Anna climbs the stairs in 12.6 s what is her power output?

Chapter 13.1 – Work, Power, and Machines machines help do work by changing the size of an input force, the direction of the force, or both they multiply the force mechanical advantage (MA) – how much a machine multiplies force or distance, ratio between the input force and output force, or ratio between input distance and output distance mechanical advantage = 𝑜𝑢𝑡𝑝𝑢𝑡 𝑓𝑜𝑟𝑐𝑒 𝑖𝑛𝑝𝑢𝑡 𝑓𝑜𝑟𝑐𝑒 = 𝑖𝑛𝑝𝑢𝑡 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑢𝑡𝑝𝑢𝑡 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 - less force over a greater distance, same work

Chapter 13.1 – Work, Power, and Machines What is the mechanical advantage of a ramp that is 6.0 m long and 1.5 m tall? Alex pulls on the handle of a claw hammer with a force of 15 N. If the hammer has a mechanical advantage of 5, how much force is exerted on the nail in the claw?