Physical Chapter Seven Simple Machines Levers Pulleys Inclined Planes Screws Wheel & Axle Wedge Compound Machines

Machines Defined Machine A device that makes work easier Can be powered by engines/electric motors or people Simple Machines A device that does work with only one movement See first slide list of types

Six Types Levers Pulleys Inclined Plane Screw Wedge Wheel & Axle Make work easier by changing the force you exert in size, direction or both Used to overcome gravity and friction

Forces Involved Effort Force F e Force applied to the machine Resistance Force F r Force applied by the machine to overcome resistance

Kinds of Work Work Input W in Work done on a machine Work Output W out Work done by a machine

Kinds of Work Work output can never be greater than work input Work output is smaller normally because of lose of energy to heat and/or friction

Work Mathematically Work equals force times distance W=f x d

Mechanical Advantage Defined Number of times a machine multiplies the effort force Does not have a unit

Levers Defined A bar that is free to pivot or turn about a fixed point

Levers---Parts Fulcrum Fixed point Effort Arm Part of the lever on which the effort force is applied Resistance Arm Part of the lever that exerts the resistance force

Levers----Types First Class Fulcrum is located between effort and resistance forces

Levers---Types Second Class Resistance force is located between effort force and fulcrum

Levers---Types Third Class Effort force is located between resistance force and fulcrum Provide a greater range of distance and speed of motion

Pulley Defined Is a grooved wheel with a rope or chain running along the groove

Pulley---parts Axle of wheel is fulcrum Effort arm –what pull on Resistance are is what you are lifting with pulley

Pulley---Types Fixed Pulley Is attached to something that doesn’t move MA of 1

Pulley---Types Movable Pulley Attached to a construction crane Pulley moves up and down

Pulley---Types Block and Tackle Fixed and movable pulleys in any combination

Wheel and Axle Defined A simple machine consisting of two wheels of different sizes that rotate together

Wheel and Axle Gearing Up Is a wheel with teeth along its circumference Like bicycle gears

Inclined Plane Defined A sloping surface used to raise objects  ramps

Screw Defined Inclined plane that moves Inclined plane wrapped in a spiral around a cylindrical post

Wedge Defined Inclined plane that moves Inclined plane with one or two sloping sides Ax, knife

Compound Machine Defined A combination of two or more simple machines

Efficiency Defined Is a measure of how much of the work put into a machine changes to useful work put out by a machine Never 100%

Lubricants Help reduce friction Oil, grease, soap

Power Defined Rate at which work is done Is measured in watts One joule per second One kilowatt equals 1000 watts