Scientific Tutor

What is Energy?

Most sources will define energy as the ability to do work. However, you then have to define what work is. Usually following the definition route gets you nowhere. This definition is much easier to understand; Energy is the ability to move a mass (matter) against a resistance (Force). The easiest example of the use of energy is to pick an object like a book up off of a table. If you move the book up against gravity your muscles expend energy to do it. That movement of the book up means that positive energy (or work) is required. Another way to say it is that the book gained energy. The book gained what is called potential energy. You can now remove your hand from the book and it will fall. As it falls back to the table it releases that energy in the form of the crash of sound when it hits the table. If we call the table the zero point of our vertical picture then if the book is allowed to fall from the table to the floor it now requires negative energy (or does negative work) because the movement is down.

How do you think about energy in terms of chemicals and chemistry?

A molecule is held together by a bond. If you try and break it apart, you are trying to move a mass against a resistance. This is an example of positive energy use. When the atoms of certain elements come together (to form a compound) they are attracted to each other and therefore, use a negative amount of energy. Another way to say that is they release energy when they come together. So whether you are talking about moving atoms or moving books, they are both examples of how energy influences what happens.

What are the units of energy?

The units of energy are joules (J) or calories (cal). Joules are the SI unit or standard unit in science, however, calories are the more common term you will hear. When you talk about how many calories you burned during exercise you are talking about how much energy you expended. Very often in chemistry books, they will use kilojoules (kJ) or kilocalories, (kcal) so remember your metric conversions. The worst and most confusing unit that is sometimes inflicted upon students is Calories. Yes, it does not look any different then the original, but because of the capital C this means kilocalories.