chapter 14: work, power, and machines

force

distance

in science, work is the product of ------- and --------

work=force x distance

work equation

moving

for work to happen, the object must be -------- in that instant

force

motion

the amount of work done on an object depends on the direction of the ------- and the direction of the ---------

by

work is done ---- objects whose force applied goes in the direction of motion (who/what causes motion)

on

work is done ------ objects whose force applied goes in the opposite direction of motion (who/what is being moved)

box

work done on = --------

human

work done by = -------

joule (j)

the ------ is the unit for work

newton

meter

1 joule is equal to the force of 1 ------- applied on one ----- in the direction of force

kg x m/s2

remember: 1N =----------

kg x m2/s2

so units of a joule are 1 --------

rate

power is the ------ at which work is done

faster

doing work at a ----- rate gives you more power

power= work/time

power equation

watts (w)

units of power are ------

j/s

one watt= -------

horsepower

the term --------- was first defined by scottish scientist james watt (1736-1819)

746 (1hp=746 watts

after many experiments, james watt calculated that the average power that one horse put out was equal to ------ watts

there must be a force exerted on the object and it must move in the direction of the force

describe the conditions that must exist for a force to do work on an object

A power level of 1 hp is approximately equivalent to 746 watts (W)

compare the units of watts and horsepower as they relate to power

machine

a -------- is a device that changes a force

size

direction

distance

machines make work easier to do by changing the ------ or force needed, the -------- of the force, or the -------- over which the force acts

force

distance

remember that work = ------- x -------

decrease

some machines ------- the applied force, but increase the distance over which the force is exerted

force

the trade-off is that the longer the oars get, the more ---- the person has to apply in order to move the oars quickly

direction

other machines can change the ------- of the applied force

input

the force you exert on a machine is called the ------- force

distance

the distance the input force acts through is called the input --------

work

the work done by the input force through some input distance is the ------- input

output

the force that is exerted by the machine is called the ----- force

distance

the distance the output force is exerted through is the output -------

output

the output force moving through the output distance is the work -------

sometimes

in reality, this is not correct, and the work output is ------ less than the work input

 any device that makes work easier by changing a force. Machines may increase the strength of the force, increase the distance over which the force is applied, or change the direction in which the force is applied

describe what a machine is and how it makes work easier to do

Work input is work done on a machine to get the desired output. Work output is the amount of desired work that is done by a machine. For an ideal machine, the work output is equal to the work input

relate the work input to a machine to the work output of a machine

advantage

the mechanical -------- of a machine is the number of times that the machine increases the input force

higher

the mechanical advantage of part A is ------ than part B or your hand

divided

the actual mechanical advantage of a machine is equal to the output force ------- by the input force

actual mechanical advantage = output force/input force

actual mechanical advantage equation

friction

the actual mechanical advantage takes into account of ------- acting on the object

ideal

the ------- mechanical advantage is the mechanical advantage in the absence of friction

higher

without friction, the ideal mechanical advantage of a machine would be much ------- than the actual mechanical advantage

distances

calculating ideal mechanical advantage is easier than actual mechanical advantage because you can focus solely on the locations of the forces and ----- in which they act

ideal mechanical advantage= input distance/output distance

ideal mechanical advantage equation

one

in most cases, the mechanical advantage will be greater than ------ because the input distance will be larger than the output distance

efficiency

the ------- of a machine is the % of the work input that becomes work output

efficiency= work output/work input x 100%

efficiency equation

100%

because there is always some friction, the efficiency of any machine is always less than --------

The actual mechanical advantage of a machine reflects the increase or decrease in force achieved by the machine. It takes into account the force needed to overcome friction. The ideal mechanical advantage of a machine reflects the increase or decrease in force there would be without friction

compare a machine’s actual mechanical advantage to its ideal mechanical advantage

the output of a machine is always less than the input

explain why the efficiency of a machine is always less than 100%

simple

a ------- machine consists of one place to have an input force and one place of an output force

lever

a ------ is an object, or bar, that is free to move around a fixed point

fulcrum

the fixed point that the bar rotates around is called the ---

distance

the input arm of a lever is the ------ between the input force and the fulcrum

fulcrum

the output arm is the distance between the output force and the ------

first

in a ----- class lever, the fulcrum is between the input arm and the output arm

force

in a second class lever, the output ------- is located between the input force and the fulcrum

fulcrum

in a third class lever, the input force is located between the ------- and the output force

wheel

axle

a -------- and ------- is a simple machine that consists of 2 disks each with a different radius

input

output

to calculate the ideal mechanical advantage of the wheel and axle, divide the radius where the ------- force is exerted by the radius where the ------ force is exerted

inclined plane

an -------- --------- is a slanted surface along which a force moves an object to a different elevation

wedge

a -------- is a v-shaped object whose sides are 2 inclined planes sloped towards each other

higher

the thinner the edge of the wedge, the ------- the mechanical advantage

screw

a ------- is an inclined plane wrapped around a cylinder

higher

for 2 screws with the same length, the one whose threads are closer together have a ----- mechanical advantage

pulley

a -------- is another simple machine that consists of a rope that fits into a groove in a wheel

fixed

a ------- pulley is a whee; attached in a fixed location

constant

the direction of the force applied is changed in a fixed pulley, but the size of the force is --------

movable

a ------- pulley is attached to the object being moved rather than to a fixed location

direction

size

movable pulleys change both the ------- and the ------ of the input force

pulley system

a combination of fixed an moving pulleys is a --------- ----------

increases

as the number of pulleys --------, so does the mechanical advantage

compound

a ------- machine is a combination of 2 or more simple machines that operate together

The inclined plane: Examples are ramps, staircases, hilly roads, etc. The wedge: Examples are knife, axe, plough, knife, etc. Screw: Examples are A screw bolt. The wheel and axle: Examples are the steering wheel of a car, bicycle pedal, etc. lever example: shovel; pulley example: flagpole

name, describe, and give an example of each of the 6 types of simple machines

To calculate the ideal mechanical advantage of the wheel and axle, divide the radius (or diameter) where the input force is exerted by the radius (or diameter) where the output force is exerted. To calculate the ideal mechanical advantage of any lever, divide the input arm by the output arm.

describe how to determine the ideal mechanical advantage of each type of simple machine

A compound machine is a machine consisting of two or more simple machines. Some examples of compound machines are clippers, a manual pencil sharpener, a crane, and a bulldozer.

define and identify compound machines