Energy & its Transfer

Bfy the end of this unit you should be able to:

Define what energy is, the units of energy (J)
Differentiate the different forms of energy

Potential Energy: Chemical, Gravitational, Nuclear, Elastic, Magnetic and Electrostatic

Kinetic Energy: Thermal (we will use “thermal” instead of “heat”), Radiant, Sound, Electrical and Movement

Other forms of energy: Mass and Mechanical

Identify and explain the difference between energy transfers and transformations.
Describe how energy is transformed in various scenarios (e.g. when a ball is dropped from a certain height) and identify energy transformations in daily life.
Investigate heat transfer by conduction, convection, and radiation, and provide real-life examples of each.
Understand the concept of the law of conservation of energy and how it relates to energy change problems. (investigation Scipad p168)
Understand the role of insulation materials in reducing heat transfer and its practical implications.
Describe how hydroelectricity is generated and be able to state the energy transformation involved in it.

What is energy?

We use the word energy a lot in everyday life, 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.

The formal definition of energy is that it is the ability to do work.
The word "work" in physics has a very specific meaning: it means that something is exerting a force over a distance. There are different sorts of energy and different ways of classifying it. One way is to talk about active energy and potential energy.

Active energy

Active energy can be thought of as energy that is moving around or doing something. It can be further subdivided into kinetic (or movement) energy and radiant energy:

Potential Energy

Potential energy is energy that is stored, waiting to do something but not actually moving or acting.

Energy can be stored in almost anything that can cause a force, such as elastic force, gravity force or electric or magnetic forces. It can also be stored in the forces that hold together atoms in chemical bonds and in the forces that hold together the particles of atomic nucleus.

Mass: Einstein's equation E=mc2 basically says that matter is also a very concentrated form of stored energy. This equation gives the relationship when matter is changed into energy or vice versa.

Straight after the Big Bang, there was only energy - in the form of light and radiation. As the Universe cooled down, some of that energy changed into particles that were the starting material for stars and everything else made of matter in the universe.

Using Einstein's equation, one kilogram of matter is equal to 90 petajoules of energy. That is quite a lot of energy - roughly equivalent to all of NZ' electricity production for a whole year.

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.

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