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What is Energy?
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Energy
In this course, Professor Douglas Halliday (Durham University) explores energy. In the first mini-lecture, we discuss the big picture of energy, looking at types of energy, key principles, and units. In the second mini-lecture, we consider changes in energy by looking at examples of various energy exchanges involving kinetic and potential energy, heat, electrical energy, etc. The third mini-lecture introduces the concept of the conservation of energy and works through four related examples. In the fourth mini-lecture, we discuss the concept of work in greater detail and go through a couple of examples. In the fifth mini-lecture, we introduce the concepts of power and efficiency, working through some examples and looking at how to improve the efficiency of a system.
What is Energy?
In this mini-lecture, we give an overview of what energy is, focusing in particular on: (i) different types of energy; (ii) closed systems and energy conservation; (iii) the definition of energy in physics and the SI unit of energy (the Joule); (iv) converting energy into usable forms; and (v) the details of thermal energy, mechanical energy, electrical energy, mechanical energy, and natural sources of energy.
Hello.
00:00:05My name is Dr Douglas Halliday,
00:00:07and I'm a professor of physics in the physics department at Durham University.
00:00:09I've been working on developing new materials for
00:00:14thin film solar sails for about 25 years
00:00:17and looking at the development of renewable energy systems
00:00:22in this course we will look at
00:00:26energy.
00:00:29We will consider questions such as What is energy?
00:00:30Where does it come from?
00:00:34What can you do with energy?
00:00:36What simple concepts and models can you use to
00:00:38describe the impact of energy on the system?
00:00:42How can we improve our use of energy,
00:00:45making it more efficient?
00:00:48We are surrounded by energy.
00:00:51Everything we do requires energy.
00:00:53Everything we use requires energy to make it.
00:00:56Even our continued existence on Earth requires energy.
00:00:59Without energy, there would be no life on Earth.
00:01:03So what is energy? Energy exists in many different forms.
00:01:08The energy of motion. Kinetic energy,
00:01:13stored energy, potential energy, rotational energy, heat, light, mechanical,
00:01:16electrical, sound, chemical.
00:01:23These are all different types of energy that we will explore during these videos.
00:01:27There are two key principles when it comes to considering energy.
00:01:33The first is the energy is always conserved in a closed or isolated system,
00:01:37and the second is that energy is never created or destroyed.
00:01:43It is only ever converted from one type to another.
00:01:48You don't generate energy.
00:01:53You can generate electrical energy or electricity,
00:01:55but only from other forms of energy such as chemical, heat or light.
00:01:59When you consume energy, it is not removed or destroyed,
00:02:06but converted into another form of energy.
00:02:10The application of energy to a system or an object will
00:02:14alter one or more of its physical properties such as velocity,
00:02:18momentum, temperature or luminous intensity.
00:02:22You can increase or decrease the energy of a system which will
00:02:27have corresponding increase or decrease in one or more of these properties.
00:02:31In physics, we define energy as a quantitative property that can do work on a system.
00:02:39It has the S I unit of Jewel,
00:02:46which is named after the 19th century English physicist James Jewel.
00:02:49Jewel is a derived s I unit.
00:02:55So that s I unit system has seven base units from which all other units can be derived.
00:02:58These base units include mass kilogrammes, length, metres, time seconds
00:03:06and from these three base units, we can build up the S I Units of Energy or the Jewel.
00:03:14Let me show you how you can work out the units
00:03:21of energy from knowing that energy can do work in a system
00:03:24and that work equals force times distance.
00:03:28And we will explore that more in another video.
00:03:32So force equals mass times acceleration. That's Newton's second law of motion.
00:03:36In terms of units,
00:03:42acceleration is metres per second per second or M s to the power of minus two.
00:03:44Putting all this together, we get the units of force as kilogrammes,
00:03:52metres per second, per second
00:03:56force times distance then is simply kilogrammes times,
00:04:00metres squared times second to the power of minus two.
00:04:04This is the unit of Jewel, built up from the S I base unit.
00:04:09Energy is everywhere.
00:04:14The ability to efficiently convert energy from one form
00:04:15to another enables us to do many things.
00:04:19The industrial revolution is a really good historical example
00:04:22of how the availability of energy in different forms
00:04:27literally literally revolutionised the way that people lived,
00:04:31worked and travelled.
00:04:35It wasn't that the energy wasn't available.
00:04:37Of course coal and wood were available.
00:04:40It was the ability to convert energy into different
00:04:43forms such as heat to mechanical energy via steam.
00:04:46That was the key that unlocked new
00:04:51industrial and manufacturing processes on a scale
00:04:54that had hitherto not been possible.
00:04:58Machines could do work hundreds of men could in a very short time.
00:05:01Now that we know the units, let's think a bit more about different types of energy.
00:05:07Heat is a form of thermal energy. We are all familiar with temperature.
00:05:12Temperature is another S.
00:05:17I base unit measured using the unit of Kelvin, or absolute temperature zero
00:05:19C, is 273. Kelvin
00:05:26absolute zero is minus 273 degrees centigrade, or zero kelvin.
00:05:30This is the temperature at which a system will have no thermal energy,
00:05:37although in practise it cannot be achieved as it is not
00:05:42physically possible to remove all thermal energy from an object.
00:05:46What happens when you heat something up
00:05:52in a solid? The atoms are held in fixed relationship by the atomic bonds.
00:05:55These bonds prevent the atoms from moving and give us solid.
00:06:01It's physical characteristic properties.
00:06:05When increasing the temperature, the atoms vibrate more quickly.
00:06:08The thermal energy is converted to vibrational energy.
00:06:13Think about heating frozen water or ice. What happens? It eventually melts.
00:06:18This occurs when the vibrational energy becomes so large
00:06:24that the bonds that hold the water molecules together
00:06:28into a solid break
00:06:31and it melts.
00:06:33What about heating a gas? What happens?
00:06:35Well, gases consist of molecules such as carbon dioxide, nitrogen
00:06:39into oxygen or to
00:06:45these molecules are free to move.
00:06:48When you heat a gas up, the speed of the gas molecules increases
00:06:50they move more quickly.
00:06:55In this case, the thermal energy is converted into the kinetic energy.
00:06:57Consider a gas in an enclosed system,
00:07:02such as a metal container.
00:07:06If you heat a gas up in a closed container,
00:07:08the molecules move more quickly.
00:07:11Many more will bounce off the wall of the container.
00:07:14What happens when you increase the velocity of the molecules?
00:07:17They will hit the wall of the container with a larger momentum
00:07:21and increase the pressure of the gas.
00:07:25It is the collision of the gas molecules with the walls of the container
00:07:29that give a closed system of gas. Its pressure.
00:07:33Electrical energy is a form of energy we can't live without.
00:07:39Today, electricity is the flow of electrical charge or electrons for example,
00:07:42along a wire.
00:07:48Another of the S I base units is the flow of of electrical current,
00:07:50measured by the unit of AM pair,
00:07:56named after the 18th and 19th century French physicist.
00:07:58An ampere represents a unit of electrical charge,
00:08:03which flows through a point in a wire
00:08:07in one second.
00:08:10The forms of mechanical energy that you study in more detail are kinetic energy,
00:08:12the energy of motion,
00:08:18Canetti, EOS is from the Greek
00:08:20and potential energy or stored energy
00:08:22the energy that an object has because of its position relative to other bodies.
00:08:25If we consider an object of mass M in kilogrammes,
00:08:32travelling at a velocity V in metres per second,
00:08:36then we find that it's kinetic energy is one half V squared.
00:08:40In other words,
00:08:46the kinetic energy depends only on the mass and the velocity squared.
00:08:47What about units?
00:08:52Well, mass is kilogrammes
00:08:54and velocity squared is metres squared
00:08:57per second per second,
00:09:00and we get kilogrammes, metres squared seconds to the power of minus two.
00:09:02The unit of Jewel discussed before
00:09:08the US we can show that the units of
00:09:11kinetic energy are the same as other forms of energy
00:09:13potential energy can be illustrated by considering a mass M.
00:09:18If you lift up something heavy, it requires work.
00:09:22Consider lifting a mass M a certain height H, for example.
00:09:26From the floor to the table.
00:09:31It's increasing.
00:09:33Potential energy is simply given by M times g times, H N g h where h is the height.
00:09:34M is the mass and G is the gravitational constant of the earth. A fixed number.
00:09:42This gravitational constant was first introduced by Isaac
00:09:49Newton when developing his laws of gravitational motion.
00:09:53There are many natural sources of energy available to us from the Earth,
00:09:58such as fossil fuels, nuclear fuel, bio fuels, wind, hydro electricity,
00:10:02the tides and the sun.
00:10:09Fossil fuels have large amounts of energy. Hence our reliance on these
00:10:11fossil fuels are composed of dead organisms such as plants or other organic matter
00:10:17that have absorbed a large amount of energy from the sun over many years.
00:10:24This energy is stored in the large number of
00:10:30carbon bonds in this materials as chemical energy.
00:10:33These bonds were formed during the growth from the energy of sunlight.
00:10:38Burning fossil fuels releases the chemical energy as heat
00:10:43producing carbon dioxide as a byproduct of the combustion.
00:10:47Nuclear fuel produces large amounts of heat through radioactive decay.
00:10:53This is where a radioactive elements decay into
00:10:58other elements emitting nuclear particles such as protons,
00:11:02neutrons
00:11:07and others.
00:11:08The total mass of the new elements is slightly less,
00:11:10and the difference in mass is released as thermal energy.
00:11:14Einstein identified that mass and energy are equivalent
00:11:19related by the well known relationship E equals M. C squared.
00:11:23Today we have much more emphasis on renewable energy.
00:11:29What exactly does this mean?
00:11:34Well,
00:11:36it means that the original source of the energy
00:11:36does not run out or become depleted when used.
00:11:39When you burn coal, it is gone, leaving a small amount of ash.
00:11:43Examples of renewable energies are energy from the wind or the sun.
00:11:48The ultimate source of energy for these is from the sun itself, which is a star,
00:11:54a nuclear fusion reactor, converting hydrogen to helium and heavier elements.
00:12:00In this video, we have looked at the basics of energy,
00:12:07different types of energy and units of energy.
00:12:10We have also identified the important principle of the conservation of energy.
00:12:13In the next lecture,
00:12:19we will look in more detail at changes in energy
00:12:21and conversion from one form of energy to another.
00:12:24Thank you
00:12:28
Cite this Lecture
APA style
Halliday, D. (2022, January 14). Energy - What is Energy? [Video]. MASSOLIT. https://massolit.io/courses/energy
MLA style
Halliday, D. "Energy – What is Energy?." MASSOLIT, uploaded by MASSOLIT, 14 Jan 2022, https://massolit.io/courses/energy