1. Chapter 5 – Energy And Its Form
Physics
Grade 7

2. Contents What is Energy? Forms of Energy Mechanical Energy
Potential Energy
Kintetic Energy
Energy Conversion
Work
Examples
Remember
Tips
Exercises
Backup

3. Module Objectives
Under stand the concepts of Energy and Its Forms
Concepts and Components of Mechanical Energy
Energy Conversion
Concept of Work

4. What is Energy? Energy is needed for everything we do
Need energy to Walk to School, to Play, to cook food, to run a Computer etc..
Energy can be defined as the ability to do work 
Energy is measured by the work that a body can do
Different kinds of Energy exist in the Universe
Energy can do different things
It can be found in many things and takes many forms

5. Forms of Energy
Energy exists in many forms: Heat, Light, Sound, Wind, Electricity, Chemical Energy, Solar Energy, Magnetic Energy, Nuclear Energy etc.
It primarily exists in the Mechanical form which makes the body to work in the virtue of its Position or Motion

6. Mechanical Energy
Mechanical energy is the energy possessed by an object due to its motion or its position
Mechanical energy can take the form of either kinetic energy or Potential energy (comes from Latin word – to be able)
Kinetic Energy is the energy due to an object's motion (comes from Greek word - motion)
Potential energy is the stored energy due to an object's position
The position and a change in position of a body leads to Potential energy and Kinetic energy respectively

7. Potential Energy Activities to understand Potential Energy:
Potential Energy is the energy possessed by a body by virtue of it’s position
Activities to understand Potential Energy:
Catapult Activity: Take a Catapult. Hold the rubber sling at it’s end, and stretch it as shown in the figure. Do you feel a pull back? Yes, the sling tends retain the original position.
A Catapult acquires Potential energy at a stretched position

8. Potential Energy Activities (contd)
2. Compressed Spring Activity: Take a spring. Put it vertically on a table and compress the spring vertically downward. Do you feel a push back? Yes, it tends to regain it’s original position. Generally a spring acquires Potential energy ata compressed or stretched position. When this energy is released an equivalent amount of work is done. The potential energy of a compressed spring is used to fire a bullet from a gun

9. Potential Energy: Think…
Elasticity or a position sustainity of a body is the real cause of its potential energy
Know This:
An object at rest can have potential energy due to its raised position
The higher an objec t is raised above the ground level, the greater is its potential energy
Greater the mass of the body, the greater is the potential energy

10. Potential Energy and Height
Expression of Potential Energy of a body at height ‘h’:

11. Potential Energy: Know this..

12. Kinetic Energy
Kinetic Energy is the energy possesed by a body by virtue of it’s motion
It is measured by the amount of work the body can do before coming to rest

13. Kinetic Energy: Know This
In hydro power station the kinetic energy of the falling water rotates the turbines connected to an electric generator. Thus, the electric energy is generated by the Kinetic energy of the water.

14. Kinetic Energy: Activities
Let us play the game of carrom

15. Kinetic Energy: Activities (contd)
2. Have you played Cricket?

16. Kinetic Energy: Activities (contd)

17. Kinetic Energy: Activities Conclusion
Bodies in motion have Kinetic Energy
If two bodies of same size and different mass are travelling at the same speed then the body of greater mass has greater Kinetic Energy
If the speed of a body increases, its kinetic energy also increases and if the speed of the body decreases its Kinetic energy also decreases

18. Kinetic Energy: Expression

19. Kinetic Energy: Expression (contd)

20. Kinetic Energy: Practical Activity

21. Energy Conversion
Conversion between potential and kinetic energy that occur when you shoot a basketball in a basket
When the ball is positioned in your hands it has full potential energy. As you move and the ball is thrown at the basket, the potential energy is converted to kinetic energy, by the transfer of kinetic energy from your arms, to your hands, to the ball. When the ball hits the basket some of its kinetic energy was converted into potential energy and then back into kinetic energy as it hit the ground.

22. Factors Affecting the Work

23. Work: Measurment
Note: Greater is the displacement, greater is the work

24. Work: Measurment (contd)

25. Worked Examples

26. Worked Examples (contd)

27. Remember A body can have two types of energy – Potential and Kinetic
Potential energy and Kinetic energy together constitue the Mechanical Energy
The energy possessed by a body by virtue of its position or shape is called Potential energy
A moving object possess Kinetic energy
Potential energy depends on the mass of the body and the height to which it is raised
Kinetic energy depends upon the mass of the body and its velocity
Potential Energy – P.E = mgh joule
Kinetic Energy – K.E = ½ MV2 joule
Force – F = MA newton
Work done – W = Fs joule
Potential energy of a body can be increased by raising it to more height or bringing in to a definite shape
Kinetic energy of a body can be increased by increasing the force applied and reducing the friction

28. Tips
Do not step out suddenly from a moving vehicle. Otherwise kinetic energy acquired by your body will make you fall down
Try to gain more kinetic energy by running fast in athletic events, such as long jump and high jump
Do not waste energy as it can be referred as stored work

29. Excercises

30. Excercises (contd)

31. Excercises (contd)

32. Excercises (contd)

33. Excercises (contd)

34. Excercises (contd)

35. Excercises (contd)

36. Excercises (contd)

37. Excercises (contd)

38. Project Work

39. Backup Thermal Energy Chemical Energy Electrical Energy Sound Energy
Light Energy
Electrochemical Energy
Electromagnetic Energy
Nuclear Energy

40. Topic

41. Thermal Energy
Thermal energy is the part of the total potential energy and kinetic energy of an object or sample of matter that results in the system temperature. It is represented by the variable Q, and can be measured in joules
Example: Consider a hot cup of coffee. The coffee is said to possess "thermal energy", or "heat energy" which is really the collective, microscopic, kinetic and potential energy of the molecules in the coffee (the molecules have kinetic energy because they are moving and vibrating, and they have potential energy due their mutual attraction for one another - much the same way that the book and the Earth have potential energy because they attract each other). Temperature is really a measure of how much thermal energy something has. The higher the temperature, the faster the molecules are moving around and/or vibrating, i.e. the more kinetic and potential energy the molecules have

42. Chemical Energy
Chemical energy is the potential energy of a chemical substance to undergo a transformation through a chemical reaction or, to transform other chemical substances.
Example: Consider the ability of your body to do
work. The glucose (blood sugar) in your body is said to have "chemical energy" because the glucose releases energy when chemically reacted (combusted) with oxygen. Your muscles use this energy to generate mechanical force and also heat. Chemical energy is really a form of microscopic potential energy, which exists because of the electric and magnetic forces of attraction exerted between the different parts of each molecule - the same attractive forces involved in thermal vibrations. These parts get rearranged in chemical reactions, releasing or adding to this potential energy.

43. Electrical Energy
Electrical energy an energy made available by the flow of electric charge through a conductor. Wind farms, on the other hand, are examples of wind turbines that convert wind energy into electrical energy.

44. Sound Energy
Sound energy is the energy produced by vibrating sound waves
Sound waves are compression waves associated with the potential and kinetic energy of air molecules. When an object moves quickly, for example the head of drum, it compresses the air nearby, giving that air potential energy. That air then expands, transforming the potential energy into kinetic energy (moving air). The moving air then pushes on and compresses other air, and so on down the chain. A nice way to think of sound waves is as "shimmering air".

45. Light Energy
Light energy is the only form of energy that we can actually see directly. It is formed through chemical, radiation, and mechanical means. Light energy can also be converted into other forms of energy

46. Electro Chemical Energy
Electro chemical energy is the energy that involves electricity and is stored in a chemical way
Consider the energy stored in a battery. Like the example above involving blood sugar, the battery also stores energy in a chemical way. But electricity is also involved, so we say that the battery stores energy "electro-chemically".

47. Electromagnetic Energy
Electromagnetic Energy is the energy transmitted by any source of light
Consider the energy transmitted to the Earth from the Sun by light (or by any source of light). Light, which is also called "electro-magnetic radiation". Why the fancy term? Because light really can be thought of as oscillating, coupled electric and magnetic fields that travel freely through space (without there having to be charged particles of some kind around).

48. Nuclear Energy
Nuclear energy is the energy that holds the nucleus of an atom
The energy released during nuclear fission or fusion, especially when used to generate electricity.

49. Energy Conversions

50. Additional Informational Links