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Work and power (What is work?
The product of the force applied to an…
Work and power
What is work?
The product of the force applied to an object and the distance through which that force is applied
Calculating work:
W=f×d which is work=force×distance
All or part of the force must act in the direction of the movement
•work does NOT involve time,only force and distance
•no work is done when you stand In place holding an object
•labeling work: w=f×d
•newton×meter (N m)
The joule
•1 newton-meter is a quantity known as a joule (j).
named after British physicist James Prescott joule.
Power
•how quickly work is done
•amount of work done per unit time.
if two people mow two lawns of equal size and one does the job in half the time, who did more work?
•same work. Different power exerted
•power= work/ time
The watt
• a unit named after Scottish inventor James watt.
•invented the steam engine. P=w/t
•joules/second •1 watt= 1j/s
Watts
•used to measure power of light bulbs and small appliances
•an electric bill is measured in kw/hrs. • 1 kilowatt= 1000w
Types of machines
The pulley
• chain, belt, or rope wrapped around a wheel
•can either change the direction or the amount of effort force.
• ex: flag pole, blinds, stage curtain
Types of pulley
Fixed:
•can only change the direction of a force.
•MA=1
Movable:
can multiply an effort force, but cannot change direction
•MA>1
The lever
•a bar that is free to pivot, or move about a fixed point when an input force is applied
•fulcrum= the pivot point of a lever.
• there are three classes of levers based on the positioning of the effort force, resistance force, and fulcrum.
First class levers
•fulcrum is located between the effort and resistance.
•makes work easier by multiplying the effort force and changing direction
Second class lever
•resistance is found between the fulcrum and effort force.
• makes work easier by multiplying the effort force , but not changing direction
Third class lever
•effort force is located between the resistance force and the fulcrum
•does not multiply the effort force, only multiplies the distance
The wheel and axle
•a lever that rotates in a circle
• a combination of two wheels of different sizes.
•smaller wheel is termed the axle
•IMA= radius of wheel/radius of axle
The inclined plane
•a slanted surface used to raise an object
•examples; ramps,stairs, and ladders
•IMA= length of ramp/height of ramp
• can never be less than one
The wedge
•an inclined plane that moves
•examples: knife, axe, razor blade
• mechanical advantage is increased by sharpening it.
The screw
•an inclined plane wrapped around a cylinder.
the closer the threads, the greater the mechanical advantage
•examples: bolts, augers, drill bits
Compound machines
•a combination of two or more simple machines
• cannot get more work out of a compound machine than is put in.
What is a machine?
Types of work
Work input
Work done on a machine
= input force×the distance through which that force acts ( input distance)
Work output
•work done by a machine
=output force × the distance through which the resistance moves (output distance)
Work output can never be greater than work input. Link Title)))
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•a device that makes work easier
•a machine can change the size, the direction, or the distance over which a force acts.
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