UNIT 2: Physics Chapter 5: Energy (pages ) I. The Nature of Energy A. What is energy? 1. Energy- defined as the ability to do work, or the ability to cause change
2. Work- is done when a force causes something to move If you push really hard on something but it does not move, have you done work on it?
3. Energy comes in several forms (electrical, chemical, radiant, and thermal)
B. Kinetic Energy- energy of a moving object 1. Equation: 2.SI unit is a joule 3. Kinetic energy depends on objects mass and velocity
C. Potential Energy- stored energy 1. Potential energy- stored energy due to its position
2. Elastic potential energy- energy stored by something that can stretch or compress such as rubber band or spring
3. Chemical potential energy- energy stored in the chemical bonds that hold atoms together
4. Gravitational potential energy- energy stored due to the objects position above Earth’s surface
5. If an object falls, its GPE will decrease and become KE PE KE PE
II. Conservation of Energy A. Changing Forms of Energy- energy is constantly being changed from one form to another 1. Transforming electrical energy- electrical energy can be transformed into light, thermal energy, kinetic energy
2. Transforming chemical energy- engine transforms chemical potential energy into kinetic energy of moving car.
a. Some less obvious- plants convert light energy into chemical potential energy (photosynthesis)
b. Animals eat food (chemical potential energy) and convert to other forms in you body (cellular respiration) ENERGY ENERGY ENERGY
B. Conversions between kinetic and potential energy 1. Mechanical energy of a system: mechanical energy = potential energy + kinetic energy 100 PE + 0 KE = 100 ME 0 PE KE = 100 ME
2. As an object falls, GPE is converted into KE. The total mechanical energy still remains the same
3. In projectile motion, object starts with large KE, small GPE. At the top it has lower KE and higher GPE. Right before it hits the ground it has high KE and low GPE
C. Law of Conservation of Energy- states that energy cannot be created or destroyed. The same amount always exists 1. Energy conservation- try and conserve “non-renewable” resources like gasoline and coal
2. Sometimes it is hard to see law of conservation of energy at work 3. Friction and air resistance can decrease mechanical energy of a system creating thermal energy
4. Nuclear fusion can change a small amount of mass into a large amount of energy (in the Sun). Nuclei fuse together
5. Nuclear fission- converts small amount of mass into large amounts of energy. Nuclei broken apart
D. The Human Body- Balancing the Energy Equation 1. Processes in your body obey law of conservation of energy a. Chemical potential energy is your bodies fuel b. Converted into heat and energy to make your body move
2. Food energy- measured in Calories (C) a. Nutrition labels on food packages tell us how many Calories or contained
b. Chart of Calorie-Burning Activities