Presentation on theme: "Chapter 13: Work and Energy"— Presentation transcript:
1Chapter 13: Work and Energy Section 1: Work, Power, and Machines
2W = F∙d What is work? Work = force x distance 2 definitions: Work is the transfer of energyWork is exerting a force on an object in the direction of its motionWork is zero when an object is not movingIt 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 distanceW = F∙d
3W 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: WW180N = F4m = dFdW = F ∙ d = (180)(4) = 720 Joules
4𝑃= 𝑊 𝑡 Power 𝑃𝑜𝑤𝑒𝑟= 𝑤𝑜𝑟𝑘 𝑡𝑖𝑚𝑒 Power is defined as the rate at which work is doneOr how much work is done in a certain amount of timePower is measured in J/s or Watts (W)Do you know of anything measured in Watts?𝑃𝑜𝑤𝑒𝑟= 𝑤𝑜𝑟𝑘 𝑡𝑖𝑚𝑒𝑃= 𝑊 𝑡
5It would be hard to cut this wood without the saw! Simple MachinesHumans 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!
6Machines Machines help do humans work They redistribute the work Usually they allow us to:Exert less force whileGoing a longer distanceA simple machine has few or no moving parts.
7Mechanical AdvantageDefinition: How much the use of a simple machine multiplies the force being appliedThe 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.
8Simple vs. complex Simple Machine: one of 6 basic types of machines LeverPulleyWheel and axleInclined planeWedgeScrewCompound Machine: A machine made of more than one simple machine