Transcript Chapter 13: Work and Energy

CHAPTER 13: WORK AND ENERGY
Section 1: Work, Power, and Machines
WHAT IS WORK?
• 2 definitions:
• Work is the transfer of energy
• Work is exerting a force on an object in the direction of its motion
Work = force x distance
W = F∙d
• 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)
EXAMPLE
• 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
F d
180N = F
4m = d
W = F ∙ d = (180)(4) = 720 Joules
POWER
• Power is defined as the rate at which work is done
• Or how much work is done in a certain amount of time
𝑊
𝑃=
𝑡
• Power is measured in J/s or Watts (W)
• Do you know of anything measured in Watts?
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!
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.
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.
SIMPLE VS. COMPLEX
• Simple Machine: one of 6 basic types of machines
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Lever
Pulley
Wheel and axle
Inclined plane
Wedge
Screw
• Compound Machine: A machine made of more than one simple machine