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Energy: Forms and Changes

Science, Grade 6


Table Of Contents: Energy: Forms and Changes

1. Introduction to Energy

2.1. What Is Energy?
Scientists define energy as the ability to do work. Work occurs when a force is exerted on an object and causes the object to move. In this example, the energy from the football player is transferred to the training equipment. The energy of an object is measured in joules.
2.2. Energy, Work and Power
Power is the rate at which work is done, or energy is transferred. A lawn mower that can mow six lawns in an hour is more powerful than a lawn mower that can only mow two lawns in the same amount of time. Similarly, a gas stove that boils water in four minutes transfers energy at a faster rate than an electric stove that boils water in seven minutes. The gas stove is more powerful than the electric stove. Power is measured in joules per second, or watts.
2.3. Types of Energy
There are two types of energy, potential and kinetic. The energy that is stored or exists because of the position of an object is called potential energy. A parked car and a stretched rubber band have potential energy. The energy of a moving object is called kinetic energy. Any object in motion has kinetic energy.

2. Pause and Interact

3.1. Review: Energy, Work, Power
Use the whiteboard text tools to complete the table.

3. Potential and Kinetic Energy

4.1. Potential Energy
An object does not have to be moving to have energy. Some objects have energy because of their shape or position. An archer uses energy to pull back on the string of the bow, and changes its shape. At this point, the bow and string have potential energy. When you lift a box, you use energy that works against the force of gravity, and changes the position of the box. The held box has potential energy due to its position.
4.2. Potential Energy and Gravity
The potential energy of an object due to gravity depends on the object’s height and weight. An increase in either of these will increase the object’s potential energy. A skier at the top of a small slope has less potential energy than a skier of the same weight who is at the top of a higher slope. Similarly, if two skiers are at the top of the same slope, the skier who weighs more has more potential energy. When these skiers begin skiing down the hill, their potential energy changes to kinetic energy.
4.3. Calculating Gravitational Potential Energy
To calculate gravitational potential energy, multiply height times weight. The box is at a height of 1.5 meters and weighs 40 Newtons. The box’s potential energy equals 60 joules. The skier is at a height of 50 meters and weighs 500 Newtons. The skier’s potential energy equals 25,000 joules.
4.4. Kinetic Energy
Kinetic energy is the energy of motion. Objects in motion have the ability to do work. Wind in motion can move rocks across the surface of the Earth. A hammer in motion can drive a nail into a board. The amount of kinetic energy an object has depends on its mass and velocity. An increase in either of these will increase the object’s kinetic energy.
4.5. Calculating Kinetic Energy
The equation for calculating kinetic energy is one-half times mass times velocity squared. A ball that weighs .3 kg and is moving at 10 m/s has the kinetic energy of 15 joules. Velocity has more of an impact on an object’s kinetic energy than mass. If the ball’s mass is doubled to .6 kg, then the kinetic energy is doubled. However, if you double the velocity of the ball to 20 m/s, then the ball’s kinetic energy quadruples.

4. Pause and Interact

5.1. Review: Potential Energy
Use the whiteboard text tools to solve the problems.
5.2. Review: Kinetic Energy
Use the whiteboard text tools to solve the problems.

5. Forms of Energy

6.1. Different Forms of Energy
Energy can have many forms, including mechanical, thermal, electrical, chemical, nuclear and electromagnetic energy.
6.2. Mechanical Energy
Moving objects, such a soccer ball, have mechanical energy. The total energy of position and motion of an object is its mechanical energy. You can calculate mechanical energy by adding an object’s potential and kinetic energy. If the soccer ball has 40 joules of potential energy and 80 joules of kinetic energy from its motion, then the ball has 120 joules of mechanical energy.
6.3. Thermal Energy
Thermal energy refers to the energy created by the motion of the particles within objects. The faster the particles move, the more thermal energy they have. Water can be found as a solid, liquid or gas, depending on the amount of thermal energy that is present. The ice cube, with its vibrating particles, has the least thermal energy and the water vapor, with its fast-moving particles, has the most thermal energy.
6.4. Chemical Energy
Chemical energy is the potential energy that is stored in chemical bonds. When you eat food, such as an apple, your body breaks down the molecules of sugar within the apple and creates chemical energy in the form of ATP (Adenosine Triphosphate). Other types of chemical energy include fossil fuels and explosives. For example, when coal is burned, it produces energy that can be used to supply power.
6.5. Electrical Energy
Electrical energy is produced by the movement of charged particles called electrons. Lightning is a form of natural electrical energy. The electricity you use in your home to turn on a lamp is produced by a power supply, such as a power plant. A switch allows the electricity to flow, and once the current reaches the lamp, the light is turned on. The electrical energy has been transformed to light and heat energy.
6.6. Nuclear Energy
Nuclear energy is created when changes occur within the nucleus of certain atoms. An example is found in the Sun’s core, where hydrogen nuclear fusion reactions produce large amounts of nuclear energy. This energy creates the Sun’s heat. Another example is the energy created from the nuclear fission reactions of uranium. This type of energy is used in nuclear power plants.
6.7. Electromagnetic Energy
Electromagnetic energy travels in waves that have both electrical and magnetic properties. The energy that is transferred by these waves is known as electromagnetic radiation. The electromagnetic spectrum shows the range of electromagnetic waves, including radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays and gamma rays. These are arranged on the spectrum from longest to shortest wavelength.

6. Pause and Interact

7.1. Review: Forms of Energy
Use the whiteboard text tools to complete the table.
7.2. Forms of Energy
Follow the onscreen instructions.

7. Energy Transformation and Conservation

8.1. Energy Transformation
Energy transformation, or conversion, occurs when energy is changed from one form to another. We rely on energy transformations for many important things. For example, the chemical energy of gasoline converts to thermal energy when it is burned, and then changes to mechanical energy to move a car. When a drill is plugged in, electrical energy is transformed to mechanical energy and sound.
8.2. Friction and Thermal Energy
When energy is transformed, some of the original energy is converted to thermal energy. Imagine a gyroscope that is spinning due to mechanical energy. It experiences friction with the surface it is spinning on and creates thermal energy. Eventually, the gyroscope will stop spinning when its mechanical energy has been completely transformed into thermal energy.
8.3. Conservation of Energy
As energy is transformed, the total amount of energy does not change. The law of conservation of energy states that energy cannot be created or destroyed. A roller coaster car is lifted to the top of a steep hill using mechanical kinetic energy. At the top, it has a large amount of potential energy. As it moves down the hill, it has kinetic energy again. However, some of its energy is converted to sound and to thermal energy due to friction. As it continues to move, the car’s energy decreases as it is transformed to other types of energy, but the total amount of energy does not change.

8. Pause and Interact

9.1. Review: Energy Transformation
Use the whiteboard tools to complete the activity.

9. Heat and Heat Technology

10.1. Temperature and Heat
The molecules within an object are in motion. Temperature is the measurement of the average kinetic energy of these molecules. The faster the particles are moving, the higher the temperature. Heat is the amount of thermal energy that is transferred from an object of higher temperature to an object at a lower temperature. For example, heat gets transferred from a warm surface to a cool ice cube, causing it to melt.
10.2. Types of Heat Transfer
Heat can be transferred by conduction, convection and radiation. Thermal conduction is the transfer of heat between objects that are in direct contact with each other, such as a spoon that is placed in a hot soup pan. Convection is the transfer of energy from a moving liquid or gas. Convection currents are created when water is boiled due to the changing density of the water. Radiation is the transfer of heat through electromagnetic waves. The radiation of the Sun travels through space and transfers thermal energy to the Earth’s atmosphere.
10.3. Using Heat to Produce Electricity
Modern technology has found many applications for heat. One of the best uses of heat is to produce electricity. The burning of fossil fuels produces heat that boils water and creates steam. The steam turns turbines in generators to produce electricity.
10.4. Heat Technology
Our vehicles use internal combustion engines to burn gasoline and create thermal energy. Within the engine, thermal energy is transformed to mechanical energy to make the car move. In other technologies, such as refrigerators and air conditioners, thermal energy is removed from an area in order to decrease the temperature.

10. Pause and Interact

11.1. Review
Use the whiteboard tools to complete the table.

11. Sources of Energy

12.1. Nonrenewable and Renewable Resources
The energy we use every day comes from a variety of sources. Fossil fuels, such as oil and coal, are nonrenewable. Uranium that provides nuclear energy is also nonrenewable. These energy resources cannot be replaced, or they take a very long time to replace. Other energy sources, such as solar and wind energy, are powered by renewable resources that are replaced immediately and are basically considered limitless.
12.2. Fossil Fuels
Fuel is a material that has stored potential energy. Today, most of our energy comes from fossil fuels which were formed millions of years ago from layers of decaying plants and animals and sediment that experienced high pressure and heat within the Earth. The chemical energy stored in the decaying organic matter is the source of potential energy found in fossil fuels.
12.3. Use of Fossil Fuels
Our society is highly dependent on coal, petroleum and natural gas. For hundreds of years coal has been mined and then burned to provide thermal and electrical energy. Petroleum is found deep within the Earth. Many products are made from petroleum including gasoline, wax, oil, asphalt, and even plastics. Natural gas is often found in petroleum deposits. We use natural gas to heat homes and run appliances.
12.4. Nuclear Energy
Uranium is a source of energy for nuclear power plants. Uranium atoms are split in nuclear fission reactions which create thermal energy to boil water. The steam is used to turn a turbine and run an electrical generator. Nuclear power plants provide electricity for millions of people and, unlike the burning of fossil fuels, produce very little air pollution. However, the complexity of these energy plants and the safety issues surrounding radioactive materials, have raised concerns about nuclear energy in the past.
12.5. Renewable Resources
Due to limited resources of fossil fuels, it is important to focus on the development of alternative sources of energy. Scientists and engineers work together to create technologies to harness the energy from renewable resources, such as the sun and wind. Solar cells use the energy from the Sun and convert it to electricity. Wind turbines are also used to create electricity. The kinetic energy of the wind turns the blades and runs a generator. The energy from moving water can also be used to produce electricity. For example, the potential energy of water in a reservoir can be converted to kinetic and electrical energy in a hydroelectric plant within a dam.

12. Pause and Interact

13.1. Review: Energy Resources
Use the whiteboard tools to complete the activity.

13. Vocabulary Review

14.1. Energy: Forms and Changes Vocabulary Matching
The molecules within an object are in motion. Temperature is the measurement of the average kinetic energy of these molecules. The faster the particles are moving, the higher the temperature. Heat is the amount of thermal energy that is transferred from an object of higher temperature to an object at a lower temperature. For example, heat gets transferred from a warm surface to a cool ice cube, causing it to melt.

14. Virtual Investigation

15.1. Energy Transformation
How does the potential and kinetic energy of an object change when it is falling? In this virtual investigation, you will drop several objects (jumbo marshmallow, water balloon, bowling ball, boulder) from two different heights and observe a transformation from potential to kinetic energy. Before the object is dropped, you will calculate its gravitational potential energy. Then, you will drop the object, calculate its kinetic energy. While conducting the investigation you can make observations and comparisons about the effects of mass, height and velocity on the energy of an object. Note: You should assume there is no air resistance on the falling objects.

15. Assessment

16.1. Energy: Forms and Changes
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