| A | B |
|---|
| work | transfer of energy that occurs when a force makes an object move |
| 2 conditions for work to have been done | applied force makes object move; movement in same direction as applied force |
| formula for caluculating work | work = force x distance; W = F x d |
| power | amount of work done in one second (rate at which work is done) |
| watt | SI unit of power (joules/second) |
| formula for calculating power | power (in watts) = work (in joules)/time (in seconds) |
| machine | device that makes work easier |
| 3 ways machines make work easier | 1. increase force applied to object; 2. increase distance over which work applied; 3. change direction of applied force |
| input force | force applied to machine |
| output force | force applied by machine |
| input work | work (force x distance) done on machine |
| output work | work (force x distance) done by machine |
| ideal machine | perfect machine in which no work is converted to heat from friction |
| mechanical advantage | ratio of output force to input force (# of times machine multiplies the input force); MA = output force/input force |
| efficiency | % of input work that is changed into useful output work |
| simple machine | machine that does the work with only one movement of machine |
| 6 simple machines | lever, pulley, wheel and axle, inclined plane, screw, wedge |
| lever | bar that is free to pivot or turn around a fixed point |
| fulcrum | fixed point on which lever pivots |
| input arm | distance from fulcrum to point where input force applied |
| output arm | distance from fulcrum to point where output force is exerted by lever |
| 3 classes of levers | 1st class; 2nd class; 3rd class |
| 1st class lever | fulcrum between input force and output force; output force in opposite direction from input force (e.g., seesaw) |
| 2nd class lever | output force between fulcrum and input force and in same direction as input force (e.g., wheelbarrow) |
| 3rd class lever | input force between fulcrum and output force and in same direction as output force (e.g., baseball bat) |
| pulley | grooved wheel with rope, chain or cable running along groove |
| fixed pulley | attached to something that doesn't move; changes direction of force |
| block and tackle | system of fixed and moveable pulleys; reduces force needed to lift object |
| wheel and axle | shaft or axle attached to center of larger wheel; wheel and axle rotate together |
| inclined plane | sloping surface that reduces the amount of force needed to do work |
| screw | inclined plane wrapped around post |
| wedge | inclined plane with one or two sloping sides |
| compound machine | two or more simple machines that organize together |
