Haryana State Board HBSE 9th Class Science Notes Chapter 11 Work and Energy Notes.
Haryana Board 9th Class Science Notes Chapter 11 Work and Energy
→ All living beings need energy for livelihood.
→ We get energy from food.
→ Green plants get energy from sunlight.
→ Two conditions are compulsory for doing work:
(a) A force should act on an object.
(b) The object must be displaced.
→ Work has only magnitude not direction.
→ Work done is negative when the force acts opposite to the direction of displacement.
→ Work done is positive when the force is in the direction of displacement.
→ Sun is the largest natural source of energy for us.
→ We can also get energy from the nucleus of atoms, internal parts of the earth and tides.
→ The unit of work and energy is joule. (1 kilojoule = 1000 J)
→ The kinetic energy of an object increases with its speed.
→ The units of power used in daily life: kilowatt and magawatt.
1 kilowatt (kW) = 1000 watt (W)
→ One horse power is equal to 746 watt.
→ The heat energy of the sun is the result of the energy released by the nuclear reactions between its inner part and on its surface.
→ The kinetic energy of water is converted into electric energy by hydro electric apparatus.
→ Fossil fuel is made of the remains of plants and animals.
→ The energy in fossil fuels is used to obtain electricity, temperature and mechanical energy.
→ When a body falls from height, its potential energy is transferred into kinetic energy.
→ The kinetic energy of a body of mass m moving with velocity v, is equal to ½mv2
→ The gravitational potential energy of a body of mass m lifted to a height h from the surface of earth is equal to mgh.
→ Work: When the force is applied on an object it moves in the direction of force, it is said to be work done.
→ Energy: The capacity of doing work is called energy.
→ Kinetic Energy: The energy possessed by an object due to its motion is called kinetic energy. Kinetic energy = ½ mv2.
→ Potential Energy: The energy possessed by a body due to its position or change in shape is called potential energy. Potential energy = mgh.
→ Mechanical Energy: The sum of kinetic energy and potential energy of an object is called mechanical energy.
→ Joule: Work done is said to be one joule when a force of 1 newton acting on an object and object is displaced through 1 m in the direction of force.
→ Displacement: The minimum distance between two position of an moving object is known as displacement.
→ Escape Velocity: That minimum velocity with this an object gone upward through the gravitational force of earth is term as escape velocity.
→ Power: The rate of doing work is called power. Its SI unit is watt. (1 watt = 1 joule/1 second).
→ Law of Conservation of Energy: According to law of conservation of energy, Energy can neither be created nor destroyed but can only be transferred from one form to another.
→ Gravitational Potential Energy: The gravitational potential energy of an object at a point above the ground is defined as the work done in raising it from the ground to that point against gravity.
→ Elastic Potential Energy: The energy possessed by an object due to change in its shape is called elastic potential energy as in stretched rubberband.
→ One Kilowatt Hour Energy: The energy used in one hour at the rate of 1 kW is called 1 kWh.