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Work, Power, Efficiency, and Simple Machines

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Natalie Howell

on 15 March 2015

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Transcript of Work, Power, Efficiency, and Simple Machines

Unit 6
Work, Power, Efficiency, and Simple Machines
Simple Machine
This is a type of lever.
Wheel and Axle
A grooved wheel that turns by the actions of a rope in the groove.
Pulley
A straight, slanted surface such as a ramp that makes it easier to move heavy objects.
Inclined Plane
An inclined plane wrapped around a central bar.
Screw
An inclined plane turned on its side.
Wedge
Work
When a force acts upon an object causing it to move.
Work = force x distance
= 10 N x 1 m
= 10 joules
Ex. An object is pushed with a force of 10N causing it to move 1m. How much work was done?
Power
The amount of work per unit time.
power = work/time
= joule/second
= watt
1 horsepower = 746 watts
Ex. Which of the following situations involves more power: 200J of work done in 10s or 50J of work done in 5s? Explain.
Efficiency
Must have input work (what you put into it) and output (what you get out of it) work
Output work is NEVER more than input work
efficiency = output work/input work x 100
Ex. What is the efficiency of a machine if the input work is 150J and the output work is 75J?
Questions
Which is an example of work?
a. holding books in your arms
b. pushing a box across the room
c. pushing on a door that will not open
d. holding weights above your head
A device with few, if any, moving parts that makes it easier to do work.
What is the relationship between work, power, and efficiency?
Lever
A simple machine with a bar and a pivot point (fulcrum).
Since only a small portion of the wheel touches the ground at a time, friction is reduced.
Also a type of lever.
Instead of helping to move things up, it helps to push things apart.
Ex. knife, shovel
Compound Machine
Two or more simple machines combined.
Ex. scissors, can opener
Compound machines are less efficient than simple machines - more friction
Can't get more out than you put in
Full transcript