Work, energy, & power

• • Work done = force x distance moved in the direction of the force
  • W = Fx
• Work done = energy transferred
• Work done at an angle to motion:

  • The component of the force F in the direction of motion is F x cos theta
  • Work done W = (F x cos theta)X
  • W = Fxcos theta
• Energy --> the capacity for doing work
• Kinetic energy --> the energy due to the movement of an object
• Gravitational potential energy --> the energy due to the position of an object in the Earth's gravitational field
• Chemical energy --> the energy contained within the chemical bonds between atoms
• Elastic potential energy --> energy stored in an object as a result of reversible change in its shape
• Electrical potential energy --> energy of electrical charges due to their position in an electrical field
• Nuclear energy --> energy within the nuclei of atoms
• Electromagnetic energy --> energy associated with all EM waves stored within the oscillations electric & magnetic fields
• Sound energy --> energy of mechanical waves due to the movement of atoms
• Internal energy --> the sum of the random potential & kinetic energies of atoms in a system
• Principle of conservation of energy --> the total energy of a closed system remains constant: energy can never be created or destroyed, but it can be transferred from one form to another
• Ek = 1/2 x m x v^2
• Ep = mgh
• Gravitational potential energy --> the capacity for doing work as a result of an object's position in a gravitational field
• Energy & power:

  • Power is the rate of work done
  • P = W/t
  • Power is the rate of energy transfer
• Power & motion:

  • A constant force F moves the car a distance x in a time t
  • Work done by the force W = Fx
  • P = W/t = Fx / t
  • The speed v of the car is (x/t), therefore P=Fv
• Efficiency:

  • The total energy of a closed system remains constant
  • Thermal losses can mean that some of the input energy is not converted into useful output energy
  • efficiency = useful output energy/ total input energy x100
  • The greater the efficiency, the greater the percentage of input energy converted