Work, energy and power

Defining Work, Energy and Power

  • Work is done when a force makes an object move. It is calculated by multiplying the applied force by the distance moved in the direction of the force. The unit is joule (J).
  • Energy is the ability to do work. It is transferred between objects or converted from one form to another. The unit is also the joule (J).
  • Power is the rate at which work is done or energy is transferred. The unit of power is watt (W), which is a joule per second (J/s).

Types of Energy

  • Kinetic energy is the energy possessed by objects in motion. Its formula is 1/2mv², where m is mass and v is velocity.
  • Potential energy is the energy stored in an object due to its position or state. The two primary types are gravitational potential energy and elastic potential energy.

Principle of Energy Conservation

  • The law of conservation of energy states that energy cannot be created or destroyed, but only transformed from one form to another or transferred from one object to another.
  • The total amount of energy in a closed system remains constant.

Work-Energy Theorem

  • The work-energy theorem relates the work done on an object to the change in its kinetic energy. It states that the total work done on an object is equal to the change in its kinetic energy.

Measuring Power

  • Power is measured as the rate of doing work or transforming energy. The formula is power (P) = work done (W) / time taken (t).

Efficiency

  • The efficiency of a device is the ratio of the useful power output to the total power input. It is usually expressed in percentage.
  • Efficiency = (useful power output / total power input) x 100%.
  • No device is 100% efficient because some energy is always lost as waste energy, such as heat and sound.

Energy and Forces

  • Work done by a force on an object is equal to the force times the distance moved in the direction of the force.
  • There are two types of forces that can act on an object: non-conservative forces which do work against an object’s motion and conservative forces like gravity which store potential energy.

Kinetic Energy and Momentum

  • Momentum is a vector quantity that is the product of mass and velocity.
  • Kinetic energy is a scalar quantity that depends on both an object’s mass and the square of its velocity.

Gravitational Potential Energy

  • Gravitational potential energy is the energy stored in an object due to its height above the ground. It is given by the product of an object’s weight and its height.
  • Gravitational potential energy = mgh, where m is mass, g is the acceleration due to gravity and h is height.

Elastic Potential Energy

  • Elastic potential energy is the energy stored in an elastic object when it is stretched or compressed. It is given by the formula 1/2kx², where k is the spring constant and x is the displacement from equilibrium.