Work and Machines
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71 terms
Terms | Definitions |
|---|---|
 basic equation for work | W = FD |
| work | the product of the force applied to the object in the direction of motion and the distance the object moves |
| joule | the SI unit or work, defined as a newton-meter |
| foot-pound | the British unit of work, the ft-lb |
| erg | the the cgs unit of work, defined as a dyne-meter |
| equation for motion away from the direction of applied force | W = FD cos Ɵ |
| the sum of individual work equals | total work |
| work accomplished | the area under the curve formed by plotting force against distance |
| integration | the method in calculus that allows determination of the area under any curve |
| negative work | force applied opposite to motion |
| net work | the sum of positive work and negative work |
| power | the time rate of doing work |
| average power | P(av) = W/t |
| watt | the SI unit of power (W), defined as one joule per second |
| foot-pound per second | the British, or FPS, unit of power, (ft-lb/s) |
| erg per second | the cgs unit of power, erg/s |
| horse-power | (hp) 550 ft-lb/s; how much weight a horse could lift through a distance of one foot in one second |
| six simple machines | lever, inclined plane, wedge, screw, pulley, and wheel and axle |
| fulcrum | a point on which a lever pivots freely |
| load | an object resting on one end of a lever, if a force is exerted at the other end |
| input force | F(i), the force applied to a lever |
| output force | F(o), the force applied to a load |
| input distance | the distance through which an input force acts |
| output distance | the distance through which an output force acts |
| input lever arm | the distance from the fulcrum to the point of application of the input force |
| output lever arm | the distance from the fulcrum to the load |
| input work | the work done on a lever |
| output work | the work done on a load |
| law of levers | F(i)L(i) = F(o)L(o); the input force times the length of the input lever arm equals the output force times the length of the output lever arm |
| mechanical advantage | the ability of a machine to multiply force |
| actual mechanical advantage | AMA, the ratio of the output force to the input force, F(o)/F(i) |
| ideal mechanical advantage | IMA, what the mechanical advantage would be if there were no energy losses due to friction, flexing of the lever, or other causes, D(i)/D(o) or L(i)/L(o) |
| Class 1 Lever | a lever for which the input and load are located on opposite sides of the fulcrum |
| Class 2 Lever | a lever for which the input and load are located on the same side of a fulcrum |
| Class 3 Lever | a lever for which the input is located between the fulcrum and the load |
| IMA of an inclined plane | IMA = S/H |
| input force for an inclined plane | F(i) = F(w) sin Ɵ + u(k)F(w) cos Ɵ |
| AMA = 1/ sin Ɵ + u(k) cos Ɵ | the actual mechanical advantage of an inclined plane |
| IMA of a wedge | IMA = L/T |
| pitch of a screw | the width of a single ridge and valley |
| IMA of a screw | IMS = 2(3.14)r/P |
| block and tackle | device consisting of a combination of several pulleys |
| wheel and axle | a kind of rotary lever in which the input force is applied to the rim of one wheel and the output force is exerted at the rim of a larger or smaller wheel mounted on the same shaft |
| IMA = r(i)/r(o) | IMA of a wheel and axle |
| torque | a force that causes rotation of a wheel and axle, a screw, or any other object |
| efficiency of a machine | work output divided by work input |
| efficiency equation | efficiency = (Wo/Wi)(100%) or efficiency = (AMA/IMA)(100%) |
| mechanisms | elements that serve to transmit motion |
| three basic types of mechanisms | wrapping connector, direct-contact bodies, linkage |
| gear | a rotating wheel or cylinder with projections encircling the rim |
| gear pair | a combination of two gears |
| rack and pinion | a gear moving on a track |
| driver | the gear initiating motion |
| follower | the gear other than the driver |
| gear train | a series of gear pairs |
| spur gears | gears that transmit motion between parallel shafts |
| helical gears | gears in which the teeth follow a path that would be traced by a helix wrapped around the gear ring; they may be used to connect shafts at any angle |
| worm gear/endless screw | gears in which force is exerted by the simultaneous action of several threads |
| bevel gears | gears for transmitting motion around corners |
| pinion | the smaller of a pair of gears when the gears are different sizes |
| gear | the larger of a pair of gears when the gears are different sizes |
| gear ratio | the number of teeth on the gear divided by the number of teeth on the pinion; the speed of the pinion relative to the speed of the gear |
| rotary speed | revolutions per minute |
| rim speed | measured in cm/s or cm/min, it is the same for both gears |
| positive drive | the force applied by the driving tooth is normal to the surface of the following tooth, and the reactive force is normal to the surface of the driving tooth |
| uniform velocity ration | the driver applies an unvarying force to the follower so that it rotates smoothly |
| involute | the curve described by a point on a string as the string is unwound from a cylinder |
| cam/eccentric | a simple mechanism for changing rotary motion into oscillations |
| slider-crank mechanisms | a linkage mechanism consisting of a rotating crank, a reciprocating slider, and a shaft |
| stroke | the movement of the slider from one extreme to the other |
| throw | the distance across the circle of a crank along any diameter |
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