Work, Power, and Simple Machines Work Power Machines Simple and Compound Machines
Work Work is defined as a force acting through a distance. Work=Force x Distance W=Fd=Newtons x meters=N- m=Joule A Joule (J) is an amount of work or energy that is equivalent to applying a 1 Newton force to an object for a distance of 1 meter. Energy is the ability to do work.
Power Power is the rate at which work is done. Power=Work/Time P=W/t=Joule/s=Watt 1 Kilowatt (kW)= 1000 Watts
MachinesA machine is a device that makes work easier. Work input is the work that is put into the machine (the input distance times the input or effort force). Work output is the work that a machine does (the output distance times the output or resistant force).
Machines (continued) Machines make work easier by changing the input force or distance or by changing the direction of input force. Work is conserved. Theoretically, the work put into a machine must equal the work that comes out of a machine. In practice this never happens due to energy being lost to friction.
Machines (continued)A comparison of input work to output work is called efficiency. The efficiency of a machine is equal to work output/work input. Due to friction, no machine is 100% efficient. Machines with the smallest amount of friction are the most efficient.
Machines (continued) The mechanical advantage of a machine is also important to know. Mechanical advantage tells how many times the input force is multiplied. The greater the mechanical advantage, the less force is required to do the work. This comes at the cost of distance, however.
Simple Machines Allmachines are either one or more simple machine. There are 6 simple machines: Inclined plane, wedge, screw, lever, pulley, and wheel and axle.
Simple Machines (continued) An inclined plane is a flat, sloped surface like a ramp. The longer the inclined plane is, the less force is needed to raise the object because of the decreased slope. Therefore, longer inclined planes with less slope yield greater mechanical advantages.
Simple Machines (continued)A wedge is a moving inclined plane. Many wedges are made from two inclined planes stuck together like an ax. The longer and thinner the wedge, the greater its mechanical advantage.
Simple Machines (continued)A screw is an inclined plane wrapped around a central bar to form a spiral. A screw gets its mechanical advantage from the length of the inclined plane wrapped around it. The closer together the threads on a screw, the greater its mechanical advantage.
Simple Machines (continued) There are three classes of levers. A first class lever has a fulcrum in the middle. A second class lever has the resistance in the middle. A third class lever has the effort in the middle. Just remember FRE.
Simple Machines (continued) Notice that different classes of levers change the direction of the input force. This can sometimes make work easier. The mechanical advantage of a lever is generated by changing the length of the force or effort arm relative to the resistant arm of the lever.
Simple Machines (continued)A pulley is a rope, belt, or chain wrapped around a wheel. A fixed pulley can change the direction of input force. Pulleys can be combined in systems. The mechanical advantage of a moveable pulley system is equal to the number of lifting lines.
Simple Machines (continued)A wheel and axle is a simple machine made from two circular objects of different sizes. The wheel is the larger of the two. The mechanical advantage of a wheel is generated by the difference in the radii.
Compound MachinesA compound machine is a combination of two or more simple machines.
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