MACHINES Simple Machines A device that does work

MACHINES

Simple Machines • A device that does work in one movement • Makes work easier by changing the force you exert in size, direction, or both

Applying Force and Doing Work • Two forces are involved when a machine is used to do work • The force applied to the machine is called the effort force (Fe)

Applying Force and doing Work • The force applied by the machine to overcome resistance is called the resistance force (Fr)

Work • There are two kinds of work to be considered when a machine is used • The work done on the machine or work input (Win) • The work done by the machine or work output (Wout)

Work • Work is the product of force and distance: • W=Fxd • Work input is the product of the effort force and the distance that force is exerted • Win = Fe x de • Work output is the product of the resistance force and the distance that force is exerted • Wout = Fr x dr

Energy is always conserved (There is no free lunch) • You can never get more work out of a machine than you put in • Wout = win • In fact Wout is always smaller then Win due to energy loss due to friction

The Perfect Machine • Although a perfect machine has never been built, it helps to imagine a frictionless machine in which no energy is converted to heat • Win = Wout • Fe x de = Fr x dr

Mechanical Advantage • The number of times a machine multiplies the effort force is the mechanical advantage (MA) • MA = resistance force effort force • MA = Fr Fe

Levers • A lever is a bar that is free to pivot on a fixed point which is called a fulcrum • The part of the lever on which the effort force is applied is the effort arm • The part that exerts the resistance force is called the resistance arm

Levers • A lever makes work easier by multiplying your effort force and changing the direction of your force • The ideal mechanical advantage can be found by dividing the length of the effort arm by the length of the resistance arm • IMA = length of effort arm length of resistance arm

Types of Levers

Types of Levers • There are three types of levers that are based on the position of the effort force, resistance force, and the fulcrum • The easiest way to remember them is to just remember what is in the middle • • 1 st class – fulcrum 2 nd class – resistance 3 rd class – effort FRE

Pulleys • A pulley is a grooved wheel with a rope or chain running along the grove • A pulley works like a 1 st class lever, instead of a bar it has a rope, the axle works as the fulcrum. The two sides of the pulley are the effort and resistance arms

Pulleys • Pulleys can be fixed or movable • A fixed pulley is attached to something that doesn’t move and can change the direction of an effort force, it does not multiply the effort force • A fixed pulley will have a mechanical advantage of one

Pulleys • A movable pulley multiplies the effort force • A movable pulley will have a mechanical advantage greater than one • A single movable pulley will have a ideal mechanical advantage of 2

Block and Tackle • A block and tackle is a combination of fixed and movable pulleys • Depending on the combination they can have a lager mechanical advantage

Wheel and Axle • A wheel and axle is a simple machine consisting of two wheels of different sizes that rotate together

Wheel and Axle • An effort force is usually applied to the larger wheel • The smaller wheel, also called the axle, exerts the resistant force • In many cases the , the larger wheel doesn’t look like a typical circular wheel

Wheel and Axle • The ideal mechanical advantage of the wheel and axle can be calculated by dividing the radius of the wheel (effort arm) by the radius of the axle (resistance arm) • IMA = radius of wheel radius of axle

Gears • Gears are modified wheel and axle machines • Effort is exerted on one gear, causing the other to turn • The larger gear is the effort gear, the smaller gear is the resistance gear

Inclined Plane • An inclined plane is a sloping surface used to raise objects • An inclined plane makes work easier because it increases the distance for the amount of work done • Increased distance means that less force is needed • work = force x distance

Inclined Plane • You can calculate ideal mechanical advantage of an inclined plane using distances • IMA = __effort distance__ resistance distance • IMA = length of slope height of slope

The Screw • The screw is an example of an inclined plane that moves • It is wrapped around a cylindrical post, the threads form a tiny ramp that runs from the tip to its top

The Wedge • A wedge is an inclined plane with one or two sloping sides • Chisels, knives, and axe blades are examples • A wedge is a moving inclined plane, the material remains in one place while the wedge moves through it

Compound Machines • A compound machine is a combination of two or more simple machines • Even a tool as simple as an axe is a compound machine made up of a wedge and a lever

Mechanical Advantage of a Bicycle • The ratio of the resistance force exerted by the tires on the road to the effort force exerted by the rider on the pedals • Multi speed bikes can change gear ratios which change mechanical advantage • A MA of less than 1 sacrifices force to gain speed

Efficiency • Some energy you put into a machine is lost as thermal energy produced as a result of friction • The work put out by a machine is always less than the work put into it • Efficiency is a measure of how much of the work put into the machine is changed into useful work put out by the machine

Efficiency • Efficiency = Wout X 100% Win • Efficiency = Fr x dr X 100% Fe x de • Many machines can be made more efficient by reducing friction • This is usually done by adding a lubricant such as oil or grease

Efficiency • In the 1970’s cars were only about 15% efficient • Today cars are about 21% efficient • Most Coal power plants are only about 13% efficient

Power • Power is the rate at which work is done • To calculate power, divide the work done by the time required to do the work Power = work time P=W t

Power • Power is measured in watts, named for James Watt, who worked on the steam engine • A watt (W) is one joule per second

Power • One watt is about equal to the amount of power used to raise a glass of water from your knees to your mouth • Large amounts of power are expressed in kilowatts • One kilowatt (k. W) = 1000 watts

Horse. Power Is the unit of power in the English system, for measuring the rate at which an engine or other prime mover can perform mechanical work. It is usually abbreviated hp. Its electrical equivalent is 746 watts, and the heat equivalent is 2545 British thermal units per hour. One horsepower was originally defined as the amount of power required to lift 33, 000 pounds 1 foot in 1 minute, or 550 foot -pounds per second. Scottish engineer and inventor James Watt established this value for the horsepower after determining in practical tests that horses could haul coal at the average rate of 22, 000 foot-pounds per minute.