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1.5

## University of Liverpool

Skip to 0 minutes and 3 seconds The laws of thermodynamics summarise the properties of energy and its transformation from one form to another. The concepts emerged during the 19th century when steam was the hot topic of the day. But it would be a mistake to think that thermodynamics is only about steam engines. It’s about almost everything, including the efficiency of engines, heat pumps, refrigerators, chemical processes, and the processes of life itself. The second law influences such things as the formation of crystals, the growth of plants, and the emergence of thoughts. But I would like to start with the first law of thermodynamics. Julius von Mayer in 1842 discovered the equivalence of heat and mechanical work.

Skip to 0 minutes and 49 seconds It allowed him to make the first announcement of the conservation of energy, which became the first law of thermodynamics. We can define energy as the capacity of a system to do work. We’re used to talking about how much energy is used in a battery and the idea that a battery is used up when the device it’s in isn’t working. In the case of this toy car, energy from the battery is used to overcome the forces of friction and drag to move the car along the table. Perhaps from physics, you’re familiar with the idea that work done is the product of force times distance moved.

Skip to 1 minute and 29 seconds So when this toy crane lifts a mass of 1/10 of a kilogramme through 1/10 of a metre, the force required to overcome gravity is mass times gravitational acceleration. So 1/10 of a kilogramme times 10 metres per second squared gives a force of 1 Newton. And the work done is force times the distance moved, or 1 Newton times 1/10 of a metre, which is 1/10 of a joule. The electrical energy comes from the battery, which performs electrical work via the motor to rotate the drum and wind up the rope. The first law of thermodynamics tells us that the electrical energy is conserved and, in this case, is converted into potential energy of the mass.

Skip to 2 minutes and 11 seconds The potential energy is the energy of a body due to its position, as opposed to the energy due to its motion, which is kinetic energy. Mayer’s breakthrough was to realise that heat was a form of energy transfer and could therefore be equated to work. I’ll talk more about heat in the next video clip. So let’s recap. Energy is the capacity to do work. Work can take many forms, including mechanical and electrical work. Similarly, energy can take forms, including kinetic and potential energy. The first law of thermodynamics is simply that energy is always conserved. It can be neither created nor destroyed.

Skip to 2 minutes and 57 seconds We can express the first law for a system experiencing a process, such as a cell in your body or the refrigerator in your kitchen, as the energy flows into the system minus the energy flows leaving the system must equal the change in energy content of the system. I’ve explained this last concept in more detail in Article 1.6 and extended it to an equation which can be applied to any system. So watch this clip again if you need to. Or go ahead and read the article.

# What is energy?

Thermodynamics connects to almost everything including the efficiency of machines, chemical reactions and the processes of life itself. Here Eann talks about the many forms of energy that we experience everyday.