Highlights of chapter 5, section 2

Transcription

1 Highlights of chapter 5, section 2

2 2 Conservation of Energy Changing Forms of Energy There are situations around us every day that involve energy changing from one form to another form. There are many words that can be used to describe this, and they all mean the same thing: Energy changing forms Energy changing from one type to another Energy transformations Energy conversions these all mean the same thing!

3 2 Transforming Electrical Energy For example, light bulbs transform electrical energy into light so you can see.

4 5.2 Conservation of Energy The Law of Conservation of Energy Energy can change from one form to another, but the total amount of energy never changes.

5 5.2 When this baseball rises and falls, the amount of kinetic energy increases and decreases, and so does its potential energy. But when added together, the total amount of KE and PE remains the same.

6 5.2 Conservation of Energy Kinetic and Potential Energy Kinetic and Potential Energy are very important types of energy. Because of this, we have given these two energies a special name.

7 5.2 Mechanical Energy Mechanical energy is the total amount of potential and kinetic energy in a system and can be expressed by this equation: mechanical energy = potential energy + kinetic energy

8 5.2 Conservation of Energy Conversions Between Kinetic and Potential Energy The mechanical energy of the ball remains constant as it rises and falls. In other words, KE + GPE together will always be the same amount of Joules of energy, from beginning to end.

9 5.2 Conservation of Energy The Law of Conservation of Energy This principle is recognized as a law of nature. The law of conservation of energy states that energy cannot be created or destroyed.

10 2 The Effect of Friction You know from experience that if you don t continue to pump a swing or be pushed by somebody else, your arcs will become lower and you eventually will stop swinging.

11 2 Conservation of Energy The Effect of Friction In other words, the mechanical (kinetic and potential) energy of the swing seems to decrease, as if the energy were being destroyed. Is this a violation of the law of conservation of energy? Is the law broken?

12 2 Conservation of Energy The Effect of Friction ii. With every movement, the swing s ropes or chains rub on their hooks, and air pushes on the rider. iii. Friction and air resistance cause some of the mechanical energy of the swing to change to thermal energy. Label the swing in your outline.

13 2 NO! The law is not broken. With every pass of the swing, the temperature of the hooks and the air increases a little, so the mechanical energy of the swing is not destroyed. Rather, it is transformed into thermal energy.

14 2 Conservation of Energy Energy Conversions in Your Body Your body stores energy in the form of fat and other chemical compounds. This chemical potential energy is used to fuel the processes that keep you alive, such as making your heart beat and digesting the food you eat.

15 2 Energy Conversions in Your Body Your body also converts this energy to heat that is transferred to your surroundings, and you use this energy to make your body move.

16 2 Conservation of Energy Food Energy The food Calorie (Cal) is a unit used by nutritionists to measure how much energy you get from various foods 1 Cal is equivalent to about 4,184 J. Next time you see a nutrition label, look closely and you will notice that the unit of measure for energy is the Calorie.

17 Why does the Sun shine?

18 Is it on FIRE? NO!

19 E = mc 2 - Einstein, 1905 It is powered by NUCLEAR ENERGY!

20 5.2 Converting Mass into Energy nuclear fusion takes place in the Sun and other stars. (we use the word nuclear because it takes place in the nucleus of an atom. Nucleus means center). During this process a small amount of mass is transformed into a tremendous amount of energy. In fusion, two small atoms come together to form one large atom plus a lot of energy!

21 Small atoms come together in

22 A Second Kind of Nuclear Reaction: F I S S I O N

23 Nuclear fission: process of splitting a large nucleus into two nuclei with smaller masses

24 A large atom is bombarded and splits into smaller atoms. plus a lot of energy is released! F I S S I O N

25 Nuclear Power Fission happens in nuclear power plants.

26 Nuclear Fission a large amount of energy is released Fission is used in nuclear reactors in power plants and submarines