Watching movies, eating hot popcorn, and many other activities depend on electrical energy. Most electrical energy comes from the burning of fossil fuels, which contain stored chemical energy. When fossil fuels are burned, the chemical energy changes to thermal energy and the thermal energy is then used to generate electrical energy. These are all examples of energy conversion. Energy conversion is the process in which one kind of energy changes into another kind. When energy changes in this way, the energy isn’t used up or lost. The same amount of energy exists after the conversion as before. Energy conversion obeys the law of conservation of energy, which states that energy cannot be created or destroyed.
Besides electrical, chemical, and thermal energy, some other forms of energy include mechanical and sound energy. Any of these forms of energy can change into any other form. Often, one form of energy changes into two or more different forms. For example, the popcorn machine below changes electrical energy to thermal energy. The thermal energy, in turn, changes to both mechanical energy and sound energy.
Kinetic-Potential Energy Changes
Mechanical energy commonly changes between kinetic and potential energy. Kinetic energy is the energy of moving objects. Potential energy is energy that is stored in objects, typically because of their position or shape. Kinetic energy can be used to change the position or shape of an object, giving it potential energy. Potential energy gives the object the potential to move. If it does, the potential energy changes back to kinetic energy.
That’s what happened to Sari. After she and Daniel left the theater, the storm cleared and they went for a swim. When she was at the top of the slide, she had potential energy. Why? She had the potential to slide into the water because of the pull of gravity. As she moved down the slide, her potential energy changed to kinetic energy. By the time she reached the water, all the potential energy had changed to kinetic energy.
This text was adapted from CK12.com. It is licensed under the Creative Commons (CC BY-NC 3.0)
Key Equations
∑Einitial=∑Efinal ; The total energy does not change in closed systems
KE=1/2 mv2 ; Kinetic energy
PEg=mgh ; Potential energy of gravity
What Is Thermal Energy?
Why do the air and sand of Death Valley feel so hot? It’s because their particles are moving very rapidly. Anything that is moving has kinetic energy, and the faster it is moving, the more kinetic energy it has. The total kinetic energy of moving particles of matter is called thermal energy. It’s not just hot things such as the air and sand of Death Valley that have thermal energy. All matter has thermal energy, even matter that feels cold. That’s because the particles of all matter are in constant motion and have kinetic energy.
Thermal Energy, Temperature, and Mass
Thermal energy and temperature are closely related. Both reflect the kinetic energy of moving particles of matter. However, temperature is the average kinetic energy of particles of matter, whereas thermal energy is the total kinetic energy of particles of matter. Does this mean that matter with a lower temperature has less thermal energy than matter with a higher temperature? Not necessarily. Another factor also affects thermal energy. The other factor is mass.
Q: Look at the pot of soup and the tub of water in the Figure below. Which do you think has greater thermal energy?
Besides electrical, chemical, and thermal energy, some other forms of energy include mechanical and sound energy. Any of these forms of energy can change into any other form. Often, one form of energy changes into two or more different forms. For example, the popcorn machine below changes electrical energy to thermal energy. The thermal energy, in turn, changes to both mechanical energy and sound energy.
Kinetic-Potential Energy Changes
Mechanical energy commonly changes between kinetic and potential energy. Kinetic energy is the energy of moving objects. Potential energy is energy that is stored in objects, typically because of their position or shape. Kinetic energy can be used to change the position or shape of an object, giving it potential energy. Potential energy gives the object the potential to move. If it does, the potential energy changes back to kinetic energy.
That’s what happened to Sari. After she and Daniel left the theater, the storm cleared and they went for a swim. When she was at the top of the slide, she had potential energy. Why? She had the potential to slide into the water because of the pull of gravity. As she moved down the slide, her potential energy changed to kinetic energy. By the time she reached the water, all the potential energy had changed to kinetic energy.
This text was adapted from CK12.com. It is licensed under the Creative Commons (CC BY-NC 3.0)
Key Equations
∑Einitial=∑Efinal ; The total energy does not change in closed systems
KE=1/2 mv2 ; Kinetic energy
PEg=mgh ; Potential energy of gravity
What Is Thermal Energy?
Why do the air and sand of Death Valley feel so hot? It’s because their particles are moving very rapidly. Anything that is moving has kinetic energy, and the faster it is moving, the more kinetic energy it has. The total kinetic energy of moving particles of matter is called thermal energy. It’s not just hot things such as the air and sand of Death Valley that have thermal energy. All matter has thermal energy, even matter that feels cold. That’s because the particles of all matter are in constant motion and have kinetic energy.
Thermal Energy, Temperature, and Mass
Thermal energy and temperature are closely related. Both reflect the kinetic energy of moving particles of matter. However, temperature is the average kinetic energy of particles of matter, whereas thermal energy is the total kinetic energy of particles of matter. Does this mean that matter with a lower temperature has less thermal energy than matter with a higher temperature? Not necessarily. Another factor also affects thermal energy. The other factor is mass.
Q: Look at the pot of soup and the tub of water in the Figure below. Which do you think has greater thermal energy?
A: The soup is boiling hot and has a temperature of 100 °C, whereas the water in the tub is just comfortably warm, with a temperature of about 38 °C. Although the water in the tub has a much lower temperature, it has greater thermal energy.
The particles of soup have greater average kinetic energy than the particles of water in the tub, explaining why the soup has a higher temperature. However, the mass of the water in the tub is much greater than the mass of the soup in the pot. This means that there are many more particles of water than soup. All those moving particles give the water in the tub greater total kinetic energy, even though their average kinetic energy is less. Therefore, the water in the tub has greater thermal energy than the soup. To compare the thermal energy of some other materials, go to the following URL and click on the interactive animation “Temperature and Thermal Energy.”
http://www.absorblearning.com/media/item.action?quick=ad
Q: Could a block of ice have more thermal energy than a pot of boiling water?
A: Yes, the block of ice could have more thermal energy if its mass was much greater than the mass of the boiling water.
The particles of soup have greater average kinetic energy than the particles of water in the tub, explaining why the soup has a higher temperature. However, the mass of the water in the tub is much greater than the mass of the soup in the pot. This means that there are many more particles of water than soup. All those moving particles give the water in the tub greater total kinetic energy, even though their average kinetic energy is less. Therefore, the water in the tub has greater thermal energy than the soup. To compare the thermal energy of some other materials, go to the following URL and click on the interactive animation “Temperature and Thermal Energy.”
http://www.absorblearning.com/media/item.action?quick=ad
Q: Could a block of ice have more thermal energy than a pot of boiling water?
A: Yes, the block of ice could have more thermal energy if its mass was much greater than the mass of the boiling water.
Heat and Phase Changes
A given kind of matter has the same chemical makeup and the same chemical properties regardless of its state. That’s because state of matter is a physical property. As a result, when matter changes state, it doesn’t become a different kind of substance. For example, water is still water whether it exists as ice, liquid water, or water vapor.
The most common states of matter on Earth are solids, liquids, and gases. How do these states of matter differ? Their properties are contrasted in the Figure below. You can also watch videos about these three states of matter at the following URLs.
The most common states of matter on Earth are solids, liquids, and gases. How do these states of matter differ? Their properties are contrasted in the Figure below. You can also watch videos about these three states of matter at the following URLs.
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The amount of energy in molecules of matter determines the state of matter. Matter can exist in one of several different states, including a gas, liquid, or solid state. These different states of matter have different properties, which are illustrated in Figure below. Gasses have the most energy, and solids have the least energy.
- A gas is a state of matter in which atoms or molecules have enough energy to move freely. The molecules come into contact with one another only when they randomly collide. Forces between atoms or molecules are not strong enough to hold them together, allowing the molecules to move independently of one another.
- A liquid is a state of matter in which atoms or molecules are constantly in contact but have enough energy to keep changing positions relative to one another. Forces between atoms or molecules are strong enough to keep the molecules together but not strong enough to prevent them from moving. The particles of a liquid have enough energy to allow them to slide past one another, but not enough energy to allow them to move freely.
- A solid is a state of matter in which atoms or molecules do not have enough energy to move. They are constantly in contact and in fixed positions relative to one another. Forces between atoms or molecules are strong enough to keep the molecules together and to prevent them from moving. The particles of a solid only have enough energy to vibrate in place.
Changing States
Matter constantly goes through cycles that involve changing states. Water and all the elementsimportant to organisms, including carbon and nitrogen, are constantly recycled on Earth. As matter moves through its cycles, it changes state repeatedly. For example, in the water cycle, water repeatedly changes from a gas to a liquid or solid and back to a gas again. How does this happen?
Adding energy to matter gives its atoms or molecules the ability to resist some of the forces holding them together. For example, heating ice to its melting point (0°C) gives its molecules enough energy to move. The ice melts and becomes liquid water. Similarly, heating liquid water to its boiling point (100°C) gives its molecules enough energy to pull apart from one another so they no longer have contact. The liquid water vaporizes and becomes water vapor.
Matter constantly goes through cycles that involve changing states. Water and all the elementsimportant to organisms, including carbon and nitrogen, are constantly recycled on Earth. As matter moves through its cycles, it changes state repeatedly. For example, in the water cycle, water repeatedly changes from a gas to a liquid or solid and back to a gas again. How does this happen?
Adding energy to matter gives its atoms or molecules the ability to resist some of the forces holding them together. For example, heating ice to its melting point (0°C) gives its molecules enough energy to move. The ice melts and becomes liquid water. Similarly, heating liquid water to its boiling point (100°C) gives its molecules enough energy to pull apart from one another so they no longer have contact. The liquid water vaporizes and becomes water vapor.
This text was adapted from CK12.com. It is licensed under the Creative Commons (CC BY-NC 3.0)