Table of Contents What Is Energy? Forms of Energy Energy Transformations and Conservation Temperature, Thermal Energy, and Heat The Transfer of Heat Energy and Heat

8.1 Vocabulary Energy Kinetic energy Potential energy Gravitational potential energy Elastic potential energy

How are energy, work, and power related? Work is done when a force moves an object. When you do work on an object, some of your energy is transferred to that object. Energy is measured in joules, the same unit as work.

Power is the rate at which work is done. Since the transfer of energy is work, the power is the rate at which energy is transferred, or the amount of energy transferred in a unit of time. Power = Energy Transferred / Time Using a machine to do work allows the same amount of energy in a shorter amount of time What is energy?

What are two types of energy? The two basic types of energy are kinetic energy and potential energy. Whether energy is kinetic or potential depends on the motion, position, and shape of the object.

Kinetic Energy The kinetic energy of an object depends on its speed and mass. What Is Energy? A moving object can do work when it strikes another object and moves it.

Factors Affecting Kinetic Energy The faster an object moves, the more kinetic energy it has. Kinetic energy also increases as mass increases.

Calculating Kinetic Energy Formula for KE: »KE = (1/2)(Mass)(Speed) 2 So, a boy pulling a 10-kg wagon at a speed of 2 m/s: KE = (1/2)(10kg)(2m/s) 2 = Note that 1 kg·m 2 /s 2 = 1 joules (J)

Do changes in the mass and speed have the same effect? KE = (1/2)(10kg)(2m/s) 2 = 20 J Double the mass: KE = (1/2)(20kg)(2m/s) 2 = Double the speed: KE = (1/2)(10kg)(4m/s) 2 Why does this work this way?

Potential Energy An object does not have to be moving to have energy. Some objects have energy as a result of their shapes or positions. You can transfer energy and the object can store it for future movement. It has the potential to do work.

What Is Energy? Gravitational Potential Energy The rock climbers have gravitational potential energy, which is potential energy related to an object's height. The gravitational potential energy of an object is equal to the work done to lift it to that height.

Gravitational Potential Energy Since work is equal to force multiplied by distance, you can calculate an object’s gravitational potential energy: gravitational potential energy = weight x height So if a book has a weight of 10 N and is lifted 2 m off the ground, how much gravitational potential energy does it have?

Elastic Potential Energy Objects that can be compressed or stretches have a different type of energy. When a rubber band is stretched or a spring is squeezed, it has elastic potential energy. The more the object is stretched or compressed, the more elastic potential energy it has.

Elastic Potential Energy The energy stored in a stretched object, such as the trampoline, is elastic potential energy. Using 1 as the greatest, how would you rank the amount of elastic potential energy of the trampoline from greatest to least? What Is Energy?

What is the SI unit for each quantity? What Is Energy?

8.2 Forms of Energy The form of energy associated with the motion, position, or shape of an object is called the mechanical energy. It is a combination of its potential energy PE and its kinetic energy KE. The higher an object moves, the greater the PE and the faster an object moves, the greater the KE. You find the total mechanical energy by adding its KE and PE.

Mechanical Energy An object with mechanical energy can do work on another object, so the mechanical energy, like all forms of energy, is the ability to do work. The more mechanical energy an object has, the more work it can do.

What are other forms of energy? An object can have other forms of KE and PE associated with the particles that make up the object. Forms of energy associated with the particles of objects include nuclear energy, thermal energy, electrical energy, and electromagnetic energy, and chemical energy.

Nuclear Energy A type of potential energy called nuclear energy is stored in the nucleus of an atom. Nuclear energy is released during a nuclear reaction. Nuclear fission occurs when a nucleus splits at a nuclear power plant. Nuclear fusion occurs when the nuclei of atoms fuse, or join together. This occurs constantly at the surface of the sun, but only a small portion of this energy reaches the Earth.

Nuclear Energy Use the Venn diagram to compare and contrast nuclear fission and nuclear fusion. Forms of Energy

Thermal Energy Since particles of objects are always in constant motion, the object always has KE. If heat is applied to an object, the particles move faster. The faster they move, the greater the KE and thermal energy it has.

Electrical Energy The energy of electric charges is electrical energy. Depending upon whether the charges are moving or stored, electrical energy can be a form of KE or PE. We rely on electrical energy from batteries or electrical lines to run devices.

Electromagnetic Energy The light we see is one type of electromagnetic energy, a form of energy that travels through space in waves. The source of these waves is vibrating electrical charges, and they can travel through a vacuum or empty space. Other forms of electromagnetic energy are microwaves, x-rays, UV waves, infrared waves, and radio waves.

Chemical Energy Chemical energy is potential energy stored in chemical bonds, holding atoms together. The food we eat, matches used to light fire, and the cells in our body all use chemical energy. These bonds are broken and release energy.

Forms of Energy Many objects in this restaurant have more than one form of energy. Find three objects. Forms of Energy

8.3 Energy Transformations & Conservation All forms of energy can be transformed into other forms of energy. Single transformation is changing one form of energy into another: a toaster transforms electrical energy into thermal energy; body transforms chemical energy into mechanical energy.

Multiple Transformations Often, a series of energy transformations is needed to do work: mechanical energy is used to strike a match, that is transformed first to thermal energy, then to chemical energy then to more thermal energy and to electromagnetic energy (light).

Energy Transformations and Conservation Multiple Transformations A series of energy transformations must occur for you to ride your bike. What are the forms of energy involved in each transformation?

Kinetic and Potential Energy The transformation between potential and kinetic energy is one of the most common energy transformations. Falling Object: An object that is dropped changes from PE (at the highest point) to KE as it moves to the ground. Pendulum: As an object swings, at the highest point in the swing, it looses its KE and gains gravitational PE. At the lowest point, the object has its greatest KE and no PE.

Energy Transformations and Conservation Pendulum A continuous transformation between potential and kinetic energy occurs in a pendulum. What are the types of energy the pendulum has at positions A, B, and C?

Pole Vault: As a person plants the pole to jump, the speed decreases and the pole bends created elastic PE. This pushes the jumper up to gravitational PE at his highest point. KE then brings him back to Earth.

What is the Law of Conservation of Energy? The Law of Conservation of Energy states that when one form of energy is transformed to another, not energy is lost in the process. Energy cannot be created or destroyed. So what happens to the energy when an object stops moving?

Whenever a moving object experiences friction, some of its kinetic energy is transformed into thermal energy. Friction is the reason why no machine is 100% efficient. The output is always less than the input because some mechanical energy is always transformed into thermal energy due to friction.

Conserving Energy While You Ride Transformations between potential and kinetic energy occur during a roller coaster ride. How much potential and kinetic energy does the coaster have at each point? Energy Transformations and Conservation

Temperature, Thermal Energy, and Heat Temperature Scales The chart shows a weather report, but it does not identify the temperature scale. Which row of temperatures do you think represents Celsius?

Thermal Energy The total amount of thermal energy in an object depends on its temperature and how many particles it contains. In the top two diagrams, which chicken pot pie contains more thermal energy? How should the bottom diagram be completed to show three pies with more thermal energy than the first? Temperature, Thermal Energy, and Heat

Where Does Heat Transfer on This Beach? Heat transfer goes on all around you all the time, even on the beach. The Transfer of Heat

Type of Heat Transfer Describe the different types of heat transfer in the illustration.

Please click when finished reviewing this information. X X