Transcript: Thermal equilibrium is an important physical principle. When two substances have unequal temperatures, thermal equilibrium means that they will tend to evolve to a situation of equal temperature. At a microscopic level we know that temperature denotes the instantaneous random speed of atoms or molecules in the substance. Hot substances have faster instantaneous motions of their atoms or molecules. So when ice is dropped into a glass of water the ice melts, and the water cools...

Transcript: Thermodynamics is the name for the scientific study of the way heat flows. When materials of unequal temperatures come into contact heat will flow from the hotter to the cooler material. Isaac Newton was the first person to show that the rate of flow of thermal energy from a hotter substance to a cooler substance was proportional to the temperature difference between them. We’re all familiar with this. When we drop an ice cube in a glass of warm water heat is transferred from...

Transcript: As the temperature of a gas is raised, the microscopic motions of the atoms and molecules increase. As the velocities of the atoms and molecules increase, they collide harder and harder. At a temperature of several thousand Kelvin, the atoms or molecules collide with sufficient energy to liberate electrons from the atoms. This process continues until eventually all electrons have been liberated, and the gas consists of a sea of nuclei with surrounding electrons, all in violent...

Transcript: Gases are typically at higher temperature and much lower density than liquids or solids. The process by which a liquid becomes a gas is called vaporization. In a gas the chains between atoms and molecules are broken. The atoms and molecules move freely in straight lines with occasional collisions. As an analogy for the differences between solids, liquids, and gases, consider people standing in a gymnasium. If the people are packed densely in a gymnasium with arms linked,...

Transcript: At a slightly higher temperature than most solids we find liquids. Liquids are still high density, only slightly larger density, than the solid form of the substance. The atoms in a liquid are still in close proximity, but they have broken loose from the rigid structure or lattice and so can move freely taking the shape of the container they are in. This is the basic form of a liquid. Most substances pass from solid to liquids to a gaseous form as they are heated up. Some are...

Transcript: The lowest temperature materials in the universe are solids, such as are found for the rocky material of our solar system or other solar systems. Solids have a rigid structure with shared electrons and the atoms enclosed in close proximity. This is true whether the solid is made of individual atoms of one element such as a mass of carbon, or molecules such as glass, or a compound such as cement. There are two basic forms of solids: amorphous, where the atoms are not in any...

Transcript: There are four basic states of matter in the universe. The temperatures of transition between them depend a little bit on the chemical substance or compound involved, but in general we can say that solids correspond to temperatures of up to one or two hundred Kelvin. The microscopic motions of the atoms and molecules are one or two kilometers per second, and these substances emit far infrared thermal radiation. Liquids are somewhat hotter, temperatures of three or four hundred...

Transcript: One of the most important principles in physics is the law of conservation of energy. Energy can be neither created nor destroyed. In any closed physical system the total amount of energy is constant, although the energy may change forms multiple times. What do we mean by a closed system? We mean drawing an imaginary box around either an atom or an object or a planet such that all the processes occur within the box. Energy is conserved, but it can change forms. In an...

Transcript: It’s a fundamental principle of physics that energy can be easily and readily transformed from one form to another. Everyday life surrounds us with examples of this. For instance, in a battery the chemical energy in a stored chemical bond is converted into an electrical signal or electrical energy which can then be converted into the motion of something, say a fan, kinetic energy. In a hydroelectric dam the stored gravitational potential energy of water raised is converted into...

Transcript: There are many situations in physics and astronomy where there is a mixture of gravitational potential energy and kinetic energy, or the energy of motion. An object in orbit around another object has both. In a circular orbit, there is one-half the amount of kinetic energy as the amount of gravitational potential energy, and both are constant through the orbit. In an elliptical orbit however, the amount of each type of energy changes continuously throughout the orbit. For...

Transcript: Almost all energy on Earth has its origin with the sun. Think about the chain of events that makes it possible for you to move. That’s a form of kinetic energy of your motion. Your motion is only possible because of the food you eat. You are turning chemical energy stored in the molecules of the food you eat into stored energy in your body and then into kinetic energy. But what about the food you eat? You’re at the top of the food chain, and that energy probably came from...

Transcript: Friction is a form of thermal energy. A hundred and fifty years ago U.S. cannon maker Count Rumford noticed that when he was boring out the barrel of a cannon a lot of heat was generated, but there wasn’t a fixed amount of heat contained in the metal of the cannon, because as he used his tools continuously more and more heat was generated. The blunter tools produced more heat than sharper tools. This turns into the concept of friction, a form of thermal energy where abrasion or...

Transcript: Heat sometimes seems like a fluid. We talk about heat flowing from one place to another, objects giving off heat, or absorbing heat. Heat is actually a measure of the random disordered motion of microscopic atoms and molecules in a substance. The larger the microscopic random motions, the more the heat. This is called thermal energy, or heat energy, and as in all other forms of energy it is measured in units of joules. The fact that heat can be quantified and is truly a form...

Transcript: Kinetic energy is the energy of motion. It depends on both mass and velocity and is defined mathematically as a half times the mass times the velocity squared. Thus, kinetic energy increases linearly with mass but as the square of the velocity. A small object moving very fast can have a large kinetic energy, and a slow object that is very massive can have a large kinetic energy. If you do the calculation, you’ll actually find out that a speeding bullet really does have almost...

Transcript: Light is a form of electromagnetic energy, but it is just one example of a wide array of forms of electromagnetic energy. Light is an electromagnetic wave caused by the microscopic changing electric and magnetic fields. Light and all electromagnetic waves transmit energy from one place to another via these changing electric and magnetic fields. Even though electromagnetic energy is invisible, it carries energy from one place to another in the form of radiation.

Transcript: Gravitational energy is a form of potential energy. Any object raised in a gravitational field has the potential to do work, and this is called gravitational potential energy. For example, when water is raised above sea level and it falls through a hydroelectric plant, the gravitational potential energy of the raised water is converted into electrical energy. Anything that is dropped will of course gain energy of motion, and so you are witnessing gravitational potential energy...

Transcript: Very few books ever changed the world, but in 1543 Copernicus published such a book called On the Revolution of the Celestial Spheres. This book was the first presentation for many centuries of the idea of a heliocentric solar system, the sun at the center.

Transcript: Potential energy can be stored in electric and magnetic fields. A compass is one example of a moving object with kinetic energy created by a magnetic field. Magnets can store energy which can be released in other forms. Electrical charges can also store energy which can be released in other forms. You can feel the force of electrical charges if you have ever noticed static cling. If you rub a balloon on your head it will stick to the ceiling. In this case electrical charges...

Transcript: Chemical energy is a form of potential energy stored in the bonds between atoms and molecules. Chemical energy is released when electrons change their configuration in atoms and molecules. When wood burns, oxygen in the atmosphere reacts with the carbon to release energy. When gasoline or natural gas burns, long carbon chains are rearranged, and energy is released. In addition to being the chemical energy source of dynamite and all of our fossil fuels, all of the world’s...

Transcript: There are several broad types of energy. Energy is measured in units of calories in the English system or joules in the international system of metric units. One broad category of energy is kinetic energy, or the energy of motion. A second broad category of energy is electromagnetic energy, energy carried by waves of light and other forms of radiation. A third form of energy is heat energy which is the random microscopic motions of atoms and molecules. A final category of...

Transcript: Scientists define energy as the ability to do work. You can also think of energy as something that can cause a change. This sounds vague. But scientists have defined energy in many careful ways, and it is a clearly quantifiable concept in physics. Next time you drive your car, consider the source of its energy. Millions of years ago sunlight was intercepted as it traveled through space and was used to grow plants on the ancient Earth. Those plants died, decayed, and were...

Transcript: When you knock on a wall or a piece of metal it feels solid enough. But normal matter is actually fantastically empty, and this is a consequence of the atomic theory itself. If we need an analogy for the atom, the nucleus would be something the size of a tennis ball on the fifty yard line of a football stadium, and the electrons would form a swarm orbiting at the outer edges of the football stadium. The next atom along in a piece of solid matter would be several hundred yards...

Transcript: Atoms are tiny pieces of matter, but they are composed of even smaller particles. Orbiting the nucleus of every atom are electrons. Electrons have negative charge and a mass of only nine times ten to the minus thirty-one kilograms. There are 1,836 times lighter than a proton. The nucleus of an atom consists of a mixture of protons and neutrons. Protons are positively charged. Neutrons have no electrical charge. Both protons and neutrons have a mass of roughly 1.7 times ten...

Transcript: A radioactive element or atom is something that spontaneously decays, often into a more stable form, by the emission of one or more particles. There are three forms of emission from radioactivity. One corresponds to the emission of an alpha particle, or a helium nucleus, two protons and two neutrons bound together. The second is called beta decay, the process by which a neutron decays into a proton with the emission of an electron and a small invisible particle. The third is...

Transcript: The chemical properties of an element are defined by its atomic number, or the number of protons. In normal, electrically neutral matter there are equal numbers of protons in the nucleus and orbiting electrons. Most elements have roughly equal numbers of protons and neutrons. However, it is possible to have different elements with different numbers of neutrons and the same number of protons. Their atomic number is the same, but their atomic weights are different. These are...