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Work
• Work is energy transferred that causes the object to move in the direction of the force — no movement, no work.
• Formula for work: W = F x d• Units:
– Work – joule (J)– Force – newton (N)– Distance – meter (m)
Power
• Power is the rate at which work is done• (determines work over time)• Formula: P = W/t• Units:
– Power – watt (W)– Work – joule (J)– Time – seconds
Machines
• Machine – device that makes work easier by changing the amount of force (effort) or direction of the force
• Changing force (effort) is mechanical advantage
• Machines let you swap force for distance or distance for force….you still do the same amount of work
Pulleys – grooved wheel that holds rope or cable
Wheel and axle – 2 circular objects of different sizes (wheel is larger)
Inclined plane – straight slanted surface
Wedge – two inclined planes that move
Screw – inclined plane wrapped around a cylinder
Compound machine – made of more than one simple machine
• Mechanical advantage – number of times a machine multiples force
• Work output – work done by the machine; product of output force and the distance of the force applied
• Work input – work done on a machine; product of the input force and the distance of the force applied
• Mechanical efficiency – ratio of output to input of energy or power (divide output by input)
• Due to friction, work put into a machine is always greater the than the work output by the machine.