Work, power and machines with pitucres

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

Levers – move from a fixed point

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.