Energy. Copyright 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

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Erick Nicholson
7 years ago
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2 Energy is a substance like quantity that can cause change. Makes objects move. Makes things stop. Is needed to do work. It does NOT have mass or volume. 2

3 Energy is stored in objects using one or more storage mechanisms. flows from one storage mechanism to another storage mechanism within the same object. flows from one object to another object. 3

4 Storage Mechanisms are ways in which energy is stored in objects. Storage mechanisms fall into one of three broad categories: Potential Energy Kinetic Energy Thermal Energy 4

5 Potential Energy is energy stored in the structural composition of an object or the position of an object. Potential energy mechanisms: Gravitational Potential Energy Elastic Potential Energy Chemical Energy 5

6 Gravitational Potential Energy is stored in an object that is positioned above another object that exerts a gravitational pull on it. Examples: a boulder positioned above the earth a roller coaster at the top of a hill water stored in a reservoir above a turbine 6

7 Elastic Potential Energy is stored in an object that is compressed or stretched. Examples: the twisted rubber band in a toy airplane an archer s bow a stretched bungee cord 7

Examples: coal burned in a power generating plant steam created in

8 Chemical Potential Energy is stored in the chemical bonds of molecules and the attractive forces between molecules. Examples: coal burned in a power generating plant steam created in a power generating plant the chemicals that make up the anode and cathode in a battery 8

9 Learning Check What are the three mechanisms for storing potential energy? 9

10 Kinetic Energy is energy stored in the purposeful movement of an object. Examples: a bolder falling off a cliff to the earth below a roller coaster going down its tracks water moving past a turbine blade 10

11 Thermal Energy is energy stored in the random motion of particles (aka atoms and molecules). Examples: the random motion of hot gas particles going up a fireplace chimney. the vibrating motion of the particles that make up the brakes that are slowing down a car. the vibrating motion the particles that make up ice (even cold objects have thermal energy!) 11

12 Learning Check What are the three broad categories of energy storage mechanisms? 12

13 Energy Transfer Mechanisms transfer energy from one type of storage mechanism to another type of storage mechanism within the same object, or one object to another object The three transfer mechanisms are work heat radiation 13

14 Work transfers energy stored in one object as kinetic energy to energy stored in another object as kinetic, gravitational potential and/or elastic potential energy. Examples A person performs work to lift a box from the floor to the top shelf. This increases the gravitational potential energy of the box. A person performs work to throw a ball in the air. This transfers the kinetic energy stored in the person s hand to kinetic and gravitational potential energies stored in the ball. 14

15 Radiation transfers thermal energy stored in one object to thermal energy stored in another object. Examples When you feel the sun s warmth on your face. Radiation is transferring thermal energy stored in the sun to thermal energy stored in the molecules of your skin. When you put your hand a few inches away from a light bulb. Radiation is transferring thermal energy stored in the light bulb to thermal energy stored in the molecules of your skin. 15

16 Heat transfers thermal energy or chemical potential energy stored in one object to thermal energy or potential energy stored in another object. Examples When you use the stove to boil a pot of water. Heat is transferring thermal energy stored in the hot burner to energy that is stored in the water as thermal energy and chemical potential energy. When you use a chemical ice pack to stop the swelling of a sports injury. Heat is transferring the thermal energy stored in your body to energy that is stored in the chemicals as chemical potential energy. 16

17 Learning Check What are the 3 transfer mechanisms that transfer energy between objects? What transfer mechanism transfers energy stored as kinetic energy in one object to kinetic, gravitational potential and/or elastic potential energies? What 2 transfer mechanisms transfer energy stored as thermal energy? What transfer mechanism transfers energy stored as thermal energy and chemical potential energy? 17

18 The Law of Conservation of Energy Energy can neither be created nor destroyed during physical and chemical changes. Nuclear changes are the exception to this law and the law of conservation of matter. During nuclear changes mass is changed into energy. 18

It could be a single object or a group of objects.

19 The Law of Conservation of Energy When investigating and analyzing energy changes it is essential to clearly define the system you are investigating. A system is simply the environment you are studying. It could be a single object or a group of objects. In this picture the system could be just the coiled spring or the spring and the car. You need to define your system before you can analyze energy s effects. 19

20 The Law of Conservation of Energy Since energy can neither be created nor destroyed, the change in the system s total stored energy is equal to the energy transferred into or out of the system. changes in equal the sum of kinetic energy work thermal energy heat gravitational PE radiation elastic PE added or removed chemical PE or ΔE k + ΔE th + ΔE g + ΔE el + ΔE ch = W + Q + R Energy transferred out of a system is - and energy transferred into a system is + 20

21 Mechanical Energy is the sum of an object s energy that is stored as gravitational potential energy elastic potential energy kinetic energy 21

22 Internal Energy is the sum of all an object s energy: gravitational potential energy elastic potential energy kinetic energy thermal energy chemical potential energy Internal energy is represented by the symbol U 22

23 Learning Check What does the Law of Conservation of Energy mean? Why is it important to define the system when investigating or analyzing energy? What storage mechanisms comprise a system s internal energy? How are a system s internal energy and the energy transferred into and out of the system related? 23

24 Recording Energy Observations 24

25 Some Simplifications for Mechanics For most of the year we will be studying mechanics. Chemical potential energy is not a factor. Thermal energy is a factor in real world examples that take into account friction. Thermal energy is zero in ideal frictionless conditions. Heat and Radiation are not a factor in energy transfers. So Real World Frictionless U = E k + E g + E el + E th U = E k + E g + E el Energy Changes ΔU = W 25

26 Learning Check If an object s kinetic energy increases, was energy transferred into or out of the object? What was the energy transfer mechanism? If a rubber band s elastic potential energy decreases, was energy transferred into or out of the rubber band? What was the energy transfer mechanism? 26

In science, energy is the ability to do work. Work is done when a force causes an

What is energy? In science, energy is the ability to do work. Work is done when a force causes an object to move in the direction of the force. Energy is expressed in units of joules (J). A joule is calculated