IB DP Physics: SL复习笔记2.3.5 Power

• The power of a mechanical process is the rate at which energy is transferred
  • Since work done is equal to the energy transferred, power can also be defined as the rate of doing work or the work done per unit time
• Power can be calculated using the equation:

• Power is also used in electricity, with labels on lightbulbs which indicate their power, such as 60 W or 100 W
  • These indicate the amount of energy transferred by an electrical current rather than by a force doing work

The Watt

• Power is measured in Watts (W)
• The Watt, W, is commonly used as the unit power (and radiant flux)
  • It is defined as 1 W = 1 J s–1

• The SI unit for energy is kg m2 s–3
• One watt is defined as:

A transfer of energy of 1 J in 1 s

Power & Force

• Moving power is defined by the equation:

• This equation is only relevant where a constant force moves a body at constant velocity. Power is required in order to produce an acceleration
• The force must be applied in the same direction as the velocity

Derivation of P = Fv

• The derivation for this equation is shown below: