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
•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
•used to measure power of light bulbs and small appliances
•an electric bill is measured in kw/hrs. • 1 kilowatt= 1000w
• a unit named after Scottish inventor James watt.
•invented the steam engine. P=w/t
•joules/second •1 watt= 1j/s
•1 newton-meter is a quantity known as a joule (j).
named after British physicist James Prescott joule.
•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)
W=f×d which is work=force×distance
All or part of the force must act in the direction of the movement
Types of machines
• 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
•can only change the direction of a force.
can multiply an effort force, but cannot change direction
•a combination of two or more simple machines
• cannot get more work out of a compound machine than is put in.
•an inclined plane wrapped around a cylinder.
the closer the threads, the greater the mechanical advantage
•examples: bolts, augers, drill bits
•an inclined plane that moves
•examples: knife, axe, razor blade
• mechanical advantage is increased by sharpening it.
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 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
Third class lever
•effort force is located between the resistance force and the fulcrum
•does not multiply the effort force, only multiplies the distance
Second class lever
•resistance is found between the fulcrum and effort force.
• makes work easier by multiplying the effort force , but not changing direction
First class levers
•fulcrum is located between the effort and resistance.
•makes work easier by multiplying the effort force and changing direction
•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.
What is a machine?
Types of work
•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)))
Work done on a machine
= input force×the distance through which that force acts ( input distance)
•a device that makes work easier
•a machine can change the size, the direction, or the distance over which a force acts.