Thermal energy

Thermal energy is energy possessed by an object or system due to the movement of particles within the object or the system. Thermal energy is one of various types of energy, where 'energy' can be defined as 'the ability to do work.' Work is the movement of an object due to an applied force. A system is simply a collection of objects within some boundary. Therefore, thermal energy can be described as the ability of something to do work due to the movement of its particles.

Because thermal energy is due to the movement of particles, it is a type of kinetic energy, which is the energy due to motion. Thermal energy results in something having an internal temperature, and that temperature can be measured - for example, in degrees Celsius or Fahrenheit on a thermometer. The faster the particles move within an object or system, the higher the temperature that is recorded.

Application of Thermal Energy

Let's take a look at a simple example of thermal energy. A heated element on a stove contains thermal energy, and the more you turn up the stove, the more internal energy the stove contains. At the very basic level, this thermal energy is the movement of the molecules that make up the metal of the stove's element. I know you can't see the molecules moving, but they are. The faster the molecules, the more internal thermal energy they contain.

Now let's place a pot of water on top of the heated element. What happens? The stove works, right? Well, not as we would typically think of it. Here, 'work' is referring to 'the movement of something when a force is applied.' Specifically, the thermal energy of the stove causes the particles of the pot and eventually the water to move faster. The internal energy of the heated element is transferred to the pot and ultimately the water within the pot. This transfer of thermal energy from the stove to the pot and to the water is referred to as heat. It is very important to keep these terms straight. In this context, heat is the term we use to refer to specifically the transfer of thermal energy from one object or a system to another, transfer being the key. The thermal energy is the energy possessed within the object or within the system due to movement of particles. They're different - heat and thermal energy.

You can feel the heat if you hold your hand above the stove. The heat, in turn, speeds up the molecules within the pot and the water. If you place a thermometer in the water, as the water heats up you can watch the temperature rise. Again, an increase in internal energy will result in an increase in temperature.

What Is Chemical Energy?

Energy is the ability to do work, where work is movement of an object by some force. We use energy every day, and energy comes in different forms. Chemical energy is energy that is stored in chemicals, such as sugar and gasoline. As chemical energy is stored energy, it is a type of potential energy, which is energy stored in objects due to their location. An easy example of potential energy would be that of a bike on top of a hill where the bike's position is elevated and has the ability to roll down the hill. In the case of chemicals, the position refers to the various atoms that exist together within the chemical.

Application of Chemical Energy

Now that we understand that chemicals contain potential energy, let's explore the significance of chemical energy. In other words, what does chemical energy do for nature?

Let's play a word association game. What do you think of when I say 'The Circle of Life'? If you're like me, you probably thought of the Disney movie 'The Lion King'. Man that was a great movie! Another way of thinking about the circle of life is in terms of energy utilization within nature. Let me explain. Plants use energy from the sun to make sugar and oxygen from carbon dioxide and water. We, along with other animals, digest that sugar to release energy, so we can do work. Sugar is digested; in other words it's broken down, into carbon dioxide and water, which, in turn, is used by plants to make more sugar.

Are you getting the circle of life?

Solar energy is used by plants to create chemical energy in the form of sugar.

Chemical Energy in Everyday Life

We just talked about the fact that plants use solar energy to make sugar from carbon dioxide and water. Sugar, carbon dioxide and water are all chemicals that are held together by what we call chemical bonds or forces that hold the chemicals together. For example, all sugars are composed of carbon, oxygen and hydrogen atoms that are held together by chemical bonds. These atoms don't just stick together automatically. Rather, energy is needed to hold them together. Plants utilize solar energy to put the carbon, the hydrogen and the oxygen atoms together in the form of sugar. This is a really good example of energy transformation where energy is changed from one form to another. In this case, solar energy is converted into chemical energy that holds the sugar together and prevents it from falling apart.

We previously established that chemical energy is a type of potential energy where the energy is stored in the chemical bonds that hold the chemical together. Likewise, the potential energy can be released when the chemical bonds are broken. This is what happens when we digest the sugar that we eat. The chemical bonds in sugar are broken as the sugar is digested to carbon dioxide and water. When the chemical bonds are broken, the potential energy is released in the form of kinetic energy or energy of motion and heat or non useable energy. The kinetic energy is used to do work, such as contract our muscles and produce heat that helps to keep our bodies warm.

What is Electrical Energy?

Energy is the ability to do work, where work is done when a force moves an object. We need and we use energy every day, and energy is available in all different forms. Electrical energy is energy that's stored in charged particles within an electric field. Electric fields are simply areas surrounding a charged particle. In other words, charged particles create electric fields that exert force on other charged particles within the field. The electric field applies the force to the charged particle, causing it to move - in other words, do work.

What are Electric Fields?

Electric fields point in the direction that positive particles would move within them

Well, what are these electric fields? To better understand electrical energy, let's explore electric fields in a bit more detail. Electric fields are like gravitational fields in that both fields are areas surrounding an object that are influenced by the object. A gravitational field surrounds the earth, providing a force that pulls us down.

Likewise, electric fields surround charged sources and exert a force on other charged particles that are within the field. Have you ever heard the expression 'opposites attract'? This certainly applies to electric fields. The image on the screen shows electric fields surrounding both positive and negative sources. The arrows you see illustrate the direction that a positive test charge would move if placed within the field.

Positive objects create electric fields that repel other positive objects; therefore, the arrows are pointing away from the positive source. Negative sources create electric fields that attract positive objects; therefore, the arrows you see are directed towards the negative source. It's very important to remember the direction of the electric field always points in the direction that a positive particle would move within that field.

Electrical Energy is Potential Energy

Electrical energy is potential energy, which is energy stored in an object due to the object's position. Well, in terms of electrical energy, the object is the charged particle, and the position is the location of that charged particle within the electric field. The charged particle will have the potential to move, or do work, due to the force of the electric field.

Moving electric field charges against their natural direction adds potential energy to an object

This is much like the potential energy you would have if you rode your bike to the top of the hill. Muscular contractions in your leg muscles provide the energy to move that bike to the top of the hill. The higher you move up the hill, the more potential energy the bike will contain. At the top of the hill, gravity then provides a force that would move the bike back down the hill.

In a similar manner, to move a charge in an electric field against its natural direction of motion requires effort. For example, an external force is needed to move a positive test charge away from a negative source. The exertion of work by an external force would in turn add potential energy to the object, just like working hard to ride your bike up the hill. If the force holding the charge in place is removed, the charged particle will move within the field.

Now, effort is not required to move an object from its high potential energy location to a lower potential energy location. Just like you don't need energy to coast down a hill, the positive charge doesn't need energy to move towards the negative source. Both are natural processes. Rather, the stored potential energy due to the position of the charged particle is transformed into kinetic energy, which is energy of motion.

What Is Nuclear Energy?

Energy is the ability to do work, where work is the movement of something when an effort is applied. We need and we use energy in our lives every day. We use energy to contract our muscles and move our cars. We use energy to warm our homes and toast our bread. Scientists are busy researching new ways to make energy available for our use. The sun seems an inexhaustible source of energy. Energy from the sun lights the sky and warms the planet. The energy from the sun is a type of nuclear energy or energy created from nuclear reactions.

During nuclear fusion, the contents of the nucleus change.

What Are Nuclear Reactions?

That's easy enough, but what are nuclear reactions? Before we can define a nuclear reaction, we need to explore the basic structure of an atom. Atoms are the smallest building blocks of matter, and matter is anything that has mass and takes up space. Different atoms make up different elements; for example, hydrogen, helium, gold and silver are all elements. Each atom contains a nucleus, and the nucleus contains protons and neutrons. Electrons surround the nucleus of an atom. A nuclear reaction is a reaction that changes the nucleus of an atom. In other words, the number of protons and/or neutrons is changed as a result of a nuclear reaction.

What Do Nuclear Reactions Have to Do with Energy?

So what does this have to do with energy? The answer is simple and yet, amazingly profound. Nuclear reactions release energy. That statement is so important, I'll repeat it. Nuclear reactions release energy, and they release a lot of it! There are two types of nuclear reactions. Fission occurs when large nuclei are split into smaller fragments. Fusion occurs when small nuclei are put together to make a bigger one. Here's the amazing thing. Either way - whether it's fusion or fission - energy is released as a result of the nuclear reaction.

Let's look at an example of each type of nuclear reaction. Nuclear fission is used to generate electricity in our nuclear power plants. Fission occurs when uranium nuclei are bombarded with neutrons. The neutrons hit and split the uranium nuclei into fragments. The fission releases a lot of energy and other neutrons as well. Those other neutrons, in turn, cause a chain reaction and cause other uranium nuclei to split, and additional energy is released. Nuclear power plants can generate a lot of electricity from a very small amount of uranium and no pollution released into the atmosphere. Nuclear fission, however, produces radioactive waste that is harmful to life and has to be properly stored.

Changes in Heat and Energy

Have you ever thought of ice as solid water? Did you know that steam is water as well? Water, as well as other matter, can exist in three states or phases, and we call them solid, liquid, and gas. As ice is heated, its temperature increases, and it melts into liquid water. Likewise, as liquid water is heated, it evaporates into water vapor. These changes from one phase to another are referred to as phase changes.

Did you know that the temperature of water doesn't increase when it boils? The water's temperature increases up to boiling and then remains constant as it boils. We will use diagrams that illustrate the relationship between temperature and heat to explain how this works. Before we do that; however, we need to describe the relationship between temperature and heat.

What is Temperature?

Let's discuss temperature first. You are likely familiar with temperature as it is a common topic of conversation. We express temperature in degrees Fahrenheit, degrees Celsius, and even Kelvin, which is an absolute scale. But what is temperature? Temperature is a measure of how fast the molecules of a substance are moving. The faster the molecules move within the substance, the higher the temperature. For example, hot water molecules move faster than cold water molecules.

Hot water molecules move faster than cold water molecules and create more energy.

Temperature can be defined as the average kinetic energy of a substance, where energy is the ability to do work. Kinetic energy is energy of motion and thus reflects how fast an object is moving. The faster the object moves the more kinetic energy it contains. The faster the molecules move that make up a substance, the greater the temperature of that substance.

What is Heat?

Now, let's talk about heat. As substances are heated on a stove, in a microwave, or by the sun, energy is added to the substance. Heat can be defined as the total amount of energy contained within the substance. Where temperature reflects the average amount of kinetic energy, heat reflects the total energy. For example, two liters of boiling water has the same temperature as one liter of boiling water. However, two liters contain more heat - that is, more total energy.

Heat and Temperature Are Related

Now let's consider the relationship between temperature and heat. As substances are heated, the temperature increases. In other words, as energy is added to a substance, the molecules making up that substance move faster.

Diagram of Temperature and Heat

Now let's diagram temperature changes in water as heat is applied to the water. This will help us to understand the relationship between heat and temperature. Looking at the diagram on the screen, you will see temperature along the y-axis and heat energy along the x-axis. You can see that the temperature increases as heat is added to water within a phase. In other words, the water molecules within ice move faster.

Phase changes that occur when heat is added to water

However, temperature doesn't change as heat is added during a phase change; for example, when the ice melts. During the phase change, the added heat doesn't make the molecules move faster but rather further apart. The heat energy added during the phase change is used to overcome some of the forces that hold the molecules together, allowing them to move further away from each other. During the phase change, the added heat energy is stored as potential energy, or energy of position, as the molecules are now further apart. This is kind of like setting a mouse trap. Potential energy is stored in the mouse trap when it is set; in other words, when the position is changed.

As heat is applied to liquid water, the molecules move faster and the temperature again increases. During the phase change from liquid to gas, the added heat is stored in the molecules as, once again, potential energy, and the temperature remains constant. The added heat is used to overcome the remaining forces that hold the molecules together within the liquid. This allows the molecules to move even further apart and form a gas. Once again, the heat energy during the phase change is stored as potential energy.

While the sun is an excellent source of energy, not all forms of life can utilize the sun's energy directly. This lesson describes how plants transform the sun's energy into potential energy stored in sugar, how living organisms utilize energy in sugar to perform work, and how the relationship between photosynthesis and cellular respiration is necessary for life.

Energy and Life

Organisms use sugar as a source of energy to do work

All living things require energy to do the work necessary for survival and reproduction. This is true for bacteria, plants and animals. But what is energy? Energy is simply the ability to do work, where work is done when a force moves an object. Let's consider your own needs for a moment. You need energy to turn on and turn off your computer. You need energy to get out of bed in the morning. You even need energy to listen to this lesson and think about what it says. And, yes, you need energy to reproduce. So where does energy come from and how do we use it? On Earth, energy ultimately comes from the sun. Plants use the sun's energy to make sugar. Organisms, in turn, use sugar as a source of energy to do work.

In this lesson, we will explore how living organisms utilize energy. We will first consider how plants use energy from the sun to make sugar. Then we will explore how organisms use energy from the sugar to do work.

How Plants Transform Energy from the Sun

Plants use energy from sunlight to make sugar and oxygen from carbon dioxide and water. The process by which carbon dioxide and water are converted to sugar and oxygen using sunlight is referred to as photosynthesis. This is an endergonic reaction, meaning energy is required by the reaction. Specifically, energy is required to put the carbon dioxide and the water molecules together to form sugar. Sun provides the energy needed to drive photosynthesis, and some of the energy used to make the sugar is stored in the sugar molecule.

The sun provides the energy needed to drive photosynthesis

How Organisms Use Energy from Sugar

Now that we know how plants synthesize sugar, let's explore how organisms use the sugar as a source of energy. In short, organisms break down the sugar to release its stored energy. The energy released from the breakdown of sugar is used by the cells to make another chemical that we call adenosine triphosphate, or simply abbreviated ATP. The synthesis of ATP by cells is referred to as cellular respiration. This is an exergonic reaction as energy is released as a result of the reaction. Energy is released when the sugar is broken down into smaller parts: carbon dioxide and water. As you can see on the screen, sugar and oxygen are the reactants, and carbon dioxide and water are the products of cellular respiration. Does that reaction look familiar? Well it should, because cellular respiration is simply the reverse of photosynthesis. Photosynthesis and cellular respiration are related as the products of one become the reactants for the other. In fact, cellular respiration and photosynthesis are dependent on one another.

What is Astrophysics?

Astrophysics is the study of celestial objects such as galaxies, stars, black holes, planets, exoplanets, the Big Bang, dark matter, and dark energy. The study of cosmology is theoretical astrophysics at scales much larger than the size of particular gravitationally-bound objects in the universe.

Astrophysicists have contributed many important insights to our understanding of the universe we live in. They have discovered the approximate age and size of our universe, theorize how long our sun will last before it exhausts its nuclear fuel (dies), discover what the universe looked like billions of years ago, temperatures of planets, shapes of galaxies and the way that matter is distributed across the observable universe.

What Are We Doing With Astrophysics at the U of I?

The Center for Theoretical Astrophysics encompasses many different groups studying various aspects of astrophysics. The Illinois Relativity group focuses on the application of Einstein's theory of general relativity to forefront problems in relativistic astrophysics. The development and application of numerical relativity to tackle problems by computational means are major activities. The merger of binary compact objects (including binary black holes) and the generation of gravitational waves are areas of great interest.

The Cosmology group researches topics including but not limited to properties of clusters, Big Bang nucleosynthesis, extragalactic astronomy, the early universe, structure formation and the properties of dark matter and dark energy. Our work on the last three topics is being done in collaboration with the high energy physics group.

The Astrophysical Fluid Dynamics group is dedicated to the study of problems in astrophysics requiring numerical modeling where they often employ parallel computing.

Astrophysics at U of I is also pursued in the Department of Astronomy. All of the Physics faculty in astrophysics work closely with their colleagues in the Department of Astronomy and many have joint appointments.

What is Quantum Physics?

Quantum information science is the study of the often-bizarre-seeming features of quantum mechanics and their application to problems in information processing. These features include wave-particle duality, the principle of superposition, the intrinsic randomness of quantum mechanical measurement outcomes, and the phenomenon of entanglement. (Entanglement refers to the nonlocal correlation that can exist between quantum mechanical systems, even when the components are separated by large distances.) These phenomena are being applied to such tasks as quantum computation (which could allow an incredible speed-up over classical computation for certain types of problems); quantum cryptography (the only provably secure method of encryption, whose security is guaranteed by the laws of physics); and quantum metrology (by which measurements can be made with resolutions exceeding those allowed by classical physics).

What Are We Doing With Quantum Physics at the U of I?

Here at the University of Illinois at Urbana-Champaign, we are learning how to gain control over these exquisitely sensitive quantum systems. Photons, the tiny bundles that light travels in, act as our window into the quantum world. By using lasers as a source for our photons, we take advantage of one of their special properties: all of the photons emitted from a particular laser are quantum-mechanically identical. This allows the systematic study of how quantum systems react to manipulation, interaction with themselves, and measurement. In addition to investigating these individual photons, we can also create pairs of entangled photons. Each photon in an entangled pair contains information which is totally random, yet perfectly correlated with that of its partner. This seemingly paradoxical behavior is the essence of how quantum mechanics differs from classical mechanics. Our entangled photon source allows us to study the rudiments of quantum computing, is crucial to experiments in quantum cryptography, and provides extremely convincing evidence that the universe does not obey classical laws.

What is Biological Physics?

In 1944, physicist Erwin Schrödinger published a short book, What is Life?, that changed the course of modern biology.

Could the behavior of a living organism be explained solely by physics and chemistry? Yes, it could, Schrodinger answered. "The obvious inability of present-day physics and chemistry to account for such events," he wrote, "is no reason at all for doubting that they can be accounted for by those sciences."

It's a sentiment that has lured generations of physical scientists to biology.

For the past half-century, researchers have applied the rigorous tools of physics to help answer Schrodinger's question and unravel the fundamental mechanisms of life, but some of the most exciting challenges remain.

What Are We Doing With Biological Physics at the U of I?

The Experimental Biological Physics Research faculty's study includes, but is not limited to single-molecule methods, single-molecule fluorescence microscopy and spectroscopy, nucleic acid and protein translocation, DNA protein interactions, molecular biology, structure and dynamics of biological macro molecules.

The Theoretical and Computational Biological Physics Research faculty's study includes such ideas as bio molecular modeling of molecular motors, multiscale modeling of pattern formation, photosynthesis, cellular mechanics, multiscale modeling of cells and bionanotechnology.