Work Work: Work is said to be done when the point of application of a force moves and it is measured using the product of force and the distance moved to the direction of the force. In equation form, Work done = Force  Distance Moved (to the direction of the force) W= F  S Where, W=Work done F=Constant Force(in Newton's) S=Distance moved to the direction of force(meters) The SI unit of work is the Joule(J) A man is pushing against a solid wall but the wall remains stationary. A man is pushing a car and the car moves to the left. Holding a heavy set of weights above your head.

Work Joule: 1 Joule of work is done when a force of 1 Newton moves a distance of 1 meter. 1 Joule = 1 Newton  1 Meter; 1J = 1Nm A person is pushing a trolley in a supermarket. If the force, applied by him on the trolley is 30N, and the trolley moves a distance of 5m in the direction of the force, calculate the work done. Here, F= 30N S= 5 m W= ? W = F  S = 30  5 =150J ans

Work(on Gravitational Force): Suppose the mass of an object is “m” and height is “h”. Work = Force  Distance =Fh =mgh h An object is being lifted from the floor onto a table top, which is 2m above the ground. If the lifting force F is 20N, calculate the work done. Here, F =20N S =2m W =? W = F  S = 20  2 =40Jans An electric motor is used to lift a 5kg mass through 3m, calculate the work done by the motor. W = F  h = mg  h = 5  10  3 = 150Jans Here, m =5kg, h=3m g=10N, W=?

Energy Energy: Energy is the capacity of a body to do work. The SI unit of energy is Joule(J) Some forms of energy  Chemical Energy  Light Energy  Sound Energy  Heat Energy  Electrical Energy  Nuclear Energy  Mechanical Energy  Solar Energy  Magnetic Energy

Chemical Energy: It releases energy as a result of a chemical reaction (e.g. burning of fuel), combustion of food in the body. Example: Oil, Wood, Coal, Battery, Food. Light Energy: Light is electromagnetic spectrum that can be detected by the human eye. Light travels in straight lines. We see something that give off their own light (for example the Sun). There are also other things that use daylight or other light. They reflect light into our eyes(for example, this page). Light carries energy. Light wave can travel through empty space. Sound Energy: Sound is a form of energy that is passed from one point to another as a wave. Sound is produced by vibrating source placed in a media. The media is usually air, but it can be any gas, liquid or solid.

Heat Energy: Heat is one kind of energy, that is used to know if a matter is cold or hot. With many chemical reactions, heat is produced, sometimes, however, the reverse happens and heat energy is taken in from the surroundings. Electrical Energy: Electrical energy is important to all of us. Electricity is used to transfer energy from one place to another. Electricity current is a flow of electric charge. Nuclear Energy: Atomic bombs, nuclear reactors Mechanical Energy: I) Kinetic energy II) Potential Energy Solar Energy: Solar system is one of the main sources of energy. The sun radiates huge amounts of energy,a tiny fraction of which falls on the earth. Two main energies that we get from the sun are heat and light.

Example of where stored Potential Energy: Potential Energy is the energy stored by a body by virtue of its position or condition. For example:  An object raised above the ground has gravitational potential energy by virtue of its raised position  Rubber band has elastic potential energy by virtue of its condition. Some type of P.E. Example of where stored Gravitational P.E Water held behind a dam Chemical P.E Food and Fuels Elastic P.E Rubber Band Nuclear P.E Particles in an atomic nucleus

Gravitational Potential Energy (G. P Gravitational Potential Energy (G.P.E): This is the energy gained by an object if lifted up against the force of gravity. G.P.E = Mass  Gravitational Field Strength  Height = m  g  h Calculation of G.P.E: I) Find force needed to lift object II) Multiply this by distance lifted III) This gives work done in lifting object from the ground IV) This equal P.E is gained by object

Kinetic Energy (K.E): Kinetic energy is the energy owned by a body by virtue of its motion. Any moving object has Kinetic Energy. Kinetic Energy (K.E)= Here, Ek = Kinetic Energy(in J) m = Mass of the body(in kg) v = Speed of the body(in m/s) For two objects of the same mass at different speeds, the faster object has the greater K.E. Similarly,for two objects of different masses but moving at the same speed,the object of the greater mass has greater K.E

Law of Conservation of Energy Energy can neither be created nor destroyed in any process. It can be converted from one form to another, but the total amount remains constant. Wasted Energy: It is found that the energy output is always less then than energy input. This is mainly due to the work which must be done against frictional force. So we can write: Energy Input = Useful Energy Output + Wasted Energy Output

Power: Power is defined as the rate of transfer of energy or work done. Here, P = Power W = Work done E = Energy converted t = Time taken The SI Unit of Power is Watt(W) in symbol 1 kilowatt(kW) = 1000 watts(103 W) 1 megawatt(MW) = 1000000 watts(106W)

Efficiency: The ratio between useful energy output to the total energy input is called efficiency. Efficiency is a ratio. It has no units. We can also express it as percentage multiplying by 100% Explain the statement: “The efficiency of the power station is about 30%” Ans: It means that in a power house it is found that during the series of transfers of energy, about 70% of the energy input is wasted and lost as terminal energy. Only about 30% of the energy input is finally converted into the useful energy.