Presentation on theme: "Notes on Chapter 8 Work & Energy"— Presentation transcript:
1 Notes on Chapter 8 Work & Energy Conceptual PhysicsNotes on Chapter 8Work & Energy
2 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.
3 Work & EnergyNOTE:No work is done in sliding a book across a table. The book has gained NO ENERGY.
4 Work & Energy Power P = W / t How fast I do work is known asPowerPower is defined aswork done / time intervalP = W / t
5 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)
6 This is known as Mechanical Energy Work & EnergyWork = Δ EnergyFd = Δ E (Energy)This is known as Mechanical Energy
7 Work & EnergyMechanical Energy is energy of position or energy of movement.Energy of position is Potential (PE) = weight * heightPE = mghEnergy of movement is Kinetic (KE) = ½ mass * speed2KE = ½ m*v2
8 Conservation of Energy Work & EnergyConservation 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”
9 Work & Energy Energy of position changes to energy of movement or energy of movement toenergy of position.
10 Work output / Work input Work & EnergyMACHINES:A machine is a device used to multiply forces or to change the direction of forces.Examples are : pulley’s and lever’sHow efficient a machine works is defined as:Work output / Work inputActual Advantage / Theoretical Advantage
11 Work & EnergyPROBLEMSWhat 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?