What is Cold?

Coldness is a relative term which tells us how hot something is - in this case not very hot. We may say that it is cold outside, but to an inhabitant of Alaska, it would appear quite warm. A hot object contains more energy than a cold object. Its Temperature is higher.

So just what is Energy? ENERGY is the property of a physically identifiable object (such as a brick) which allows it to do measurable work on another object. Energy is conserved; it can neither be created nor destroyed. This simple fact is one of the most important laws of physics. It is known as the Law of Conservation of Energy. The total amount of energy in the Universe is constant. Energy is the currency of nature. No process or event can occur without energy being transferred.

Heat is one form of energy (others include electrical, chemical and nuclear). Refrigeration is concerned with moving heat. The temperature of the brick can be raised by supplying it with energy. But to cool the brick, the brick itself has to supply energy to something else. It can dissipate energy in the form of microwaves such as heat or light (if it is red-hot!). But an external source cannot focus on the brick and extract energy. It's like asking why the target cannot cannot send a bullet back to a gun.

A Further Analogy - Energy is like £££

Wealth is to the economic world as energy is to the natural world.

For example, wealth can take many forms. It may be in the form of cars, jewels, property, money in the bank, or potential earnings. Nothing in the economic world can happen unless money is transferred (wealth is transferred). The currency of the UK economic world is the pound sterling. Similarly, energy can take many forms. It may be in the form of heat, or chemical potential energy, or even in the form of mass. Nothing in the natural universe can change unless energy is transferred. The currency of the natural world is the joule.

Another similarity between wealth and energy is that whenever an event, such as the purchase of an house occurs. We never actually see the money transferred. We simply assume the transaction has taken place based on the effects we observe, namely the new owner takes up residence. Similarly, when we observe a cup of coffee cooling down, we don't actually "see" joules of energy being transferred to the surrounding air, but we assume that this is happening based on the effects that we observe (the coffee getting cooler and the surrounding air getting warmer). In the natural world, the object at the higher energy potential (temperature in this case) can be considered to be in the driving seat.

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