Notes on Chapter 8 Work & Energy Conceptual Physics Notes on Chapter 8 Work & Energy

Work & Energy W = Fd Work is defined as Force x distance Work is done in lifting a book one meter. Twice as much work is done in lifting the same book two meters.

Work & Energy NOTE: No work is done in sliding a book across a table. The book has gained NO ENERGY.

Work & Energy Power P = W / t How fast I do work is known as Power Power is defined as work done / time interval P = W / t

Work & Energy UNITS: Force (F) = Newton Distance (d) = Meters Work = N*m or Joule (J) Time (t) = Seconds (s) Power (P) = J/s or Watt (W) (NOTE: One horsepower (hp) is equal to .75 kW or 7500 W)

This is known as Mechanical Energy Work & Energy Work = Δ Energy Fd = Δ E (Energy) This is known as Mechanical Energy

Work & Energy Mechanical Energy is energy of position or energy of movement. Energy of position is Potential (PE) = weight * height PE = mgh   Energy of movement is Kinetic (KE) = ½ mass * speed2 KE = ½ m*v2

Conservation of Energy Work & Energy Conservation of Energy   “Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes”

Work & Energy Energy of position changes to energy of movement or energy of movement to energy of position.

Work output / Work input Work & Energy MACHINES: A machine is a device used to multiply forces or to change the direction of forces. Examples are : pulley’s and lever’s How efficient a machine works is defined as: Work output / Work input Actual Advantage / Theoretical Advantage

Work & Energy PROBLEMS What is the work done in lifting a 100 kg block a height of 7 m? A 40 kg boy runs up stairs to a floor 5 m high in 7 seconds. What is his power output?