ICSE Physics Class 7 Notes Chapter 3 Energy
→ Work is said to be done if the applied force on the body moves it. If no motion takes place, no work is said to be done.
→ The amount of work done depends on two factors :
- on the magnitude of the force applied (greater the force applied, greater is the work done), and
- on the distance moved in the direction of force (greater the distance moved, greater is the work done).
→ The work done by a force on a body is equal to the product of the force and the distance moved by the body in the direction of force, i.e.
Work done = Force x distance moved in the direction of force
Or W = F x d
→ The S.I. unit of work is joule (J), where 1 joule (J) = 1 newton (N) x 1 meter (m)
→ The energy of a body is its capacity (or ability) to do work. The energy of a body in a state is equal to the work done on the body to bring it to that state.
→ The S.I. unit of energy is joule (J).
→ Kinetic energy of a body is the energy possessed by it due to its motion. It is the energy stored when work is done to bring the body in motion.
→ Kinetic energy of a moving body depends on two factors :
- on the mass of the body (greater the mass of the body, greater is its kinetic energy), and
- on the speed of the body (more the speed of the body, higher is its kinetic energy).
→ The potential energy changes into the kinetic energy when it is put to use.
→ In transformation of energy, the total sum of useful and non-useful energy obtained after conversion is equal to the energy converted, i.e. the total energy remains conserved.
→ According to the conservation of mechanical energy, if friction is neglected, the total sum of potential energy and . kinetic energy remains constant. Examples are : motion of roller coaster, free vertical fall of a body etc.
→ The electricity obtained from the energy possessed by the flowing water is called the hydro-electricity.