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Chapter 13: Work and Energy

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1 Chapter 13: Work and Energy
Section 1: Work, Power, and Machines

2 W = F∙d What is work? Work = force x distance 2 definitions:
Work is the transfer of energy Work is exerting a force on an object in the direction of its motion Work is zero when an object is not moving It may hurt and you may exert a lot of force when pushing on a wall, but if the wall doesn’t move, no work was done. Work is measured in N∙m or Joules (J) Work = force x distance W = F∙d

3 W Example F d Looking for work: W 180N = F 4m = d
A heavy crate rests on the floor. How much work is needed to move it 4m across the floor if it takes 180N to push it? Looking for work: W W 180N = F 4m = d F d W = F ∙ d = (180)(4) = 720 Joules

4 𝑃= 𝑊 𝑡 Power 𝑃𝑜𝑤𝑒𝑟= 𝑤𝑜𝑟𝑘 𝑡𝑖𝑚𝑒
Power is defined as the rate at which work is done Or how much work is done in a certain amount of time Power is measured in J/s or Watts (W) Do you know of anything measured in Watts? 𝑃𝑜𝑤𝑒𝑟= 𝑤𝑜𝑟𝑘 𝑡𝑖𝑚𝑒 𝑃= 𝑊 𝑡

5 It would be hard to cut this wood without the saw!
Simple Machines Humans are lazy, so we invented machines to make life easier! Machines do not make less work; they just make it easier to do work. It would be hard to cut this wood without the saw!

6 Machines Machines help do humans work They redistribute the work
Usually they allow us to: Exert less force while Going a longer distance A simple machine has few or no moving parts.

7 Mechanical Advantage Definition: How much the use of a simple machine multiplies the force being applied The higher the number, the easier it is for the human to do the work with the machine. Different forces can do the same amount of work.

8 Simple vs. complex Simple Machine: one of 6 basic types of machines
Lever Pulley Wheel and axle Inclined plane Wedge Screw Compound Machine: A machine made of more than one simple machine

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