Work, Power & Machines Quiz

Work

Applying a force on an object that moves in the same direction of the force.

Formula for Work

Work = Force x Distance; W = F x D

Unit for Force

Newtons

Unit for Distance

Meters

Unit for Work

Joules or Newton-meter

1 kilogram equals _____ Newtons

10

To convert from kg to N, ______ by 10

multiply Kg
(move decimal one place to the right)

To convert from cm to m, _____ by 100

divide cm
(move decimal two places to the left)

Power

the rate or how fast the work is done

Formula for Power

Power = Work divided by Time; P = W / T

Unit for Power

Watts (W)

2 Ways simple machines help you do work

1) Increase the size of the force
or
2) Change the direction or the force

Incline Plane

a simple machine that is a straight, slanted surface

Input Force

the force that a person puts into the machine

Output Force

the force the machine puts out (usually the weight of the object)

Input Distance

the distance you have to apply your force

Output Distance

the distance the machine has to apply it's force

Work Input

the amount of work you do
(your force x your distance)
measured in Joules

Work Output

the amount of work the machine does
(machine's force x machine's distance)
measured in Joules

Mechanical Advantage

A ratio between output force and input force.
MA = output force / input force
the number of times the machine multiplies your force.

Force-Distance Trade-off

the less force you have to apply, the greater than distance you will have to apply that force.

Unit for Mechanical Advantage

no unit; just blank

Mechanical Efficiency

A ratio between work output and work input multiplied by 100.
ME = work output / work input X 100

Units for Mechanical Efficiency

%

Efficiency

how effective a machine is at turning your work input into it's work output.

Mechanical Efficiency in the Real World

Always less than 100%;
The closer it is to 100, the more efficient the machine;
Work Input = Work Output + Friction

Mechanical Efficiency in an Ideal World

Always = 100%;
Work Input = Work Output
(there is no friction)

Pulley

a simple machine that has a grooved wheel that holds a rope or a cable

Fixed Pulley

1) Pulley itself doesn't move
2) Changes the direction of the force only

Moveable Pulley

1) Pulley moves with the load
2) Changes the size of the force

Block and Tackle

a system that uses 2 kinds of pulleys together

Inclined Plane

a simple machine that is a straight, slanted surface. Ex: a ramp

Screw

an incline plane wrapped in a spiral around a cylinder

Compound Machine

machines that are made up of 2 or more simple machines

Wedge

a double inclined plane

Lever

a simple machine consisting of a bar that pivots at a fixed point

Fulcrum

the fixed point at which a level pivots

Wheel & Axle

a simple machine that consists of two circular objects of different sizes