Heat and energy
By the end of this unit you should be able to:
1. Describe conduction, convection, and radiation, and provide real-life examples of each.
2. Describe phase changes and explain phase transitions (e.g., melting, boiling) in terms of particle energy and bonding.
3. Describe the thermal expansion of materials and use this to explain certain phenomena.
4. Understand how energy changes form in various systems (e.g., mechanical to thermal) and identify energy transformations in daily life.
5. Evaluate the environmental and social impact of different energy sources and consumption patterns.
6. Understand the role of insulation materials in reducing heat transfer and its practical implications.
7. Explain the role of heat in biological systems, including thermoregulation and its importance in living organisms.
Energy
We use the word energy a lot, but even scientists can find it hard to define what energy is in a way easily understandable to non-scientists. Energy is something that can make things change. It doesn't weigh anything and you can't touch it, but we see it all around us. Scientists define energy as the 'ability to do work'. Work in science means a force moving something through a distance.
There are different sorts of energy and different ways of classifying it. One way is to talk about active energy and stored energy.
Active energy can be further subdivided into kinetic (or movement) energy and radiant energy:
Stored energy is called potential energy. Energy can be stored in almost anything that can cause a force, such as elastic, gravity or electric or magnetic forces. It can also be stored in chemical bonds and in the forces that hold together the atomic nucleus.
Einstein's equation E=mc2 basically says that matter is also a very concentrated form of stored energy. Straight after the big bang, there was only energy. As the Universe cooled down, some of that energy changed into the atoms that were the starting material for stars and everything else.
One kilogram of matter is equal to 90 petajoules of energy; that is about equivalent to three years production from all NZ gas fields.
One of the most important laws of science is called the Law of Conservation of Energy: Energy cannot be created or destroyed, it can only be moved around or changed into another sort of energy.
Energy transfer and energy tranformation
Energy can be transferred from one object to another.
For example, when you tee off on a golf course, kinetic energy is transferred from the club to the ball. In an energy transfer, the type of energy remains the same.
Energy can also be transformed from one type to another.
For example, when you throw an object ball straight up into the air kinetic energy is transformed into gravitational potential energy.
Whenever an energy transfer OR transformation takes place, the total amount of energy always stays the same. The unit of energy is called the joule, so the total joules has to stay the same. However, during most energy transformations some energy is changed to heat. If heat is not the energy type we want, we call the energy that is changed into the sort we want useful energy and the sort changed into heat waste energy.
Extra for experts: Although energy can't be destroyed, heat energy can only be useful (made to do work) when there is a difference in temperature.
For example, if I have hot rocks underground I can use them to do work - such as making electricity in a geothermal power station. However, I can only do this by cooling the rocks down which warms the atmosphere up. Once they reach the same temperature I can't get any more useful work out of the heat energy, even though the total amount of heat has not changed. Since heat ALWAYS naturally flows from hot to cold, that's the end of it. The energy hasn't been destroyed, but its ability to do useful work has. This is part of what is known as the Law of Entropy.