Work and Energy

• Work done on an object is the product of the magnitude of the force acting on the body and the displacement in the direction of the force, W = F.s
• The SI unit of force is Newton
• If a force acting on a body causes no displacement, the work done is 0, for example, pushing a wall
• The force component F cos θ gives the component of force along the direction in which the body is displaced, where θ is the angle between the force vector and displacement vector
• Energy is defined as the ability to do work, and its unit is the same as that of work. Energy is a scalar quantity
• SI unit of energy or work = Joule (Nm) or Kgm2s−2
• Energy has different forms: Light, heat, chemical, electrical, or mechanical. Mechanical energy is the sum of Kinetic energy (K.E) and Potential energy (P.E)
• Objects in motion possess energy and can do work. The body with a higher velocity has more Kinetic Energy (KE)
• Law of conservation of energy states that energy can neither be created nor destroyed but can be transferred from one form to another. The total energy before and after the transformation remains constant
• Total energy = KE + PE, where 1/2 mv2 + mgh = constant
• The rate of doing work or the rate of transfer of energy is called power, denoted by P. SI unit is Watt (Js−1)
• Average power = Total energy consumed / Total time taken
• The commercial unit of power is kWh, i.e., energy used in 1 hour at 1000 Joules/second. 1kWh = 3.6×106J
• When an object is raised to a certain height, work is done against gravity to change its position. This energy is stored as Potential Energy, PE = mgh
• Energy can get stored in an object when work is done on it, for example, stretching a rubber string. Potential Energy is the energy possessed by a body due to its configuration or change in position
• Factors affecting Kinetic Energy: Mass, Velocity, Momentum
• The work-energy theorem states that the net work done by a moving body can be calculated by finding the change in Kinetic Energy, Wnet = KEfinal - KEinitial
• Wnet = 1/2m(v2 - u2)