Energy forms and transformations

What is energy? We use the word all the time – but very few people have a strong understanding what it is It is a difficult thing to explain – unless you use physics to do so

Why ask? Think very carefully about your own definition or understanding about energy How would you explain energy to a young child?

Improving your understanding It seems that we take the understanding of energy for granted – it seems like such a natural concept to us – a thing that we have always experienced, or understood But how much of it do we really understand? Here’s the problem: the textbooks don’t help too much too

The official definition Work: The energy transferred to an object when a force acting on the object moves through a displacement (Note: the force must be the one responsible for the movement according to Newton’s second law) Energy: The ability to do work Though these definitions seem cyclical, it should be apparent that force and energy are linked together – where one exists, so does the other

So how do we understand energy? This is the first time that you will be dealing with energy mathematically and conceptually The best way to study energy – is to develop a way to “see” it – but this is not always easy

Because you can’t always see it The challenging thing about understanding energy is “seeing” it You can now start to understand and “see” forces as a push or pull But there are many types of energy you can’t see – but somehow, we make them do work for us

Types of energy Heat energy – transferred thermal energy between substances Kinetic energy – energy found in moving objects Gravitational potential energy – energy stored in objects raised above the ground

Heat, as an example Heat is a good example of energy that does work – even though we don’t think of it as that It isn’t something that you can always see – but we understand it because it is something we can feel But you can’t always do so - when there is very little heat - you don’t notice that it’s there

Hot or cold? For example, when things are hot – they are hot because there is a lot of heat But when things are cold – they are cold because there is little heat There is no such thing as “cold” – cold is a description of when heat is missing All types of energy are like this It can be described as a thing that can move and change from one form or another

Heat can transform into other forms of energy So how do we turn one form of energy, like heat, into another form, like electricity? Almost all of the ways we generate electricity has to rely on producing heat energy

Nuclear energy Nuclear energy is released when the nucleus of an atom is split open This type of nuclear reaction is called FISSION (splitting) This releases a large amount of energy in the form of heat

Energy can change Nuclear energy doesn’t just turn into electrical energy – it is turned into a few different types first This is another important characteristic of energy: it can be transformed into another form BUT: it cannot suddenly be created from nothing If you look carefully into everything that uses energy or creates it, you can always find out where it originally came from

So, when creating electricity from nuclear energy: Nuclear energy – created heat Heat energy – used to boil water to create steam Kinetic energy – created when steam caused turbines to turn Electrical energy – created when turning turbines moved magnet that created an electric current

Does this give you a better understanding? It is important to develop your own understanding of energy in order to better understand its characteristics and how it governs interactions in the physical world Like force, it can be a very abstract concept and system of thinking – but it is governed by only a few simple rules and simple equations

Work – the link between force and energy Let’s begin by understanding that energy is a “thing” that can flow from one place to another This characteristic is best seen in heat transfer – but it can be applied when dealing with any type of energy If energy is a “thing” that can move from one place or object to another – how does it do it?

Now it’s here – not it’s not I want you to think of this scenario – a rolling chair or cart sitting in the middle of the room Someone comes by and pushes it – what is the sequence of events?

Some simple points to point out… The chair was at rest to start The chair moved forward The chair came to a stop From a dynamics point of view – we know how to describe these events But how do we describe this in regard to energy?

Energy How did the energy flow? Energy possessed by the person Was transferred to the chair because the person did work on the chair The chair gained kinetic energy and moved Friction did work on the chair as it moved removing energy The chair lost kinetic energy and came to a stop

One way to picture energy A good way to become good at analyzing energy is developing a way to “see” it Being able to understand how an object comes to possess it – basically, how it flows from one object to another, will help you a great deal with the problems

Positive and Negative work Energy is a SCALAR value – although it is calculated by using force, a vector, and displacement, which is a vector Work can be positive or negative – but this time, the positives and negatives don’t tell you about direction Instead, if work is negative or positive, it tells you whether or not an object has GAINED or LOST energy

When does this happen? In the case of the person and the chair in the last example, the person gave energy to the chair so the energy that the chair had is POSITIVE - it gained energy This is because the force acted in the same direction as the displacement The purpose of the push from the person was to cause that displacement forward

When is it negative? Energy is lost when the force acting on the object is trying to STOP the displacement When this happens, the force is in the OPPOSITE DIRECTION to the displacement What is happening is that the force is taking energy away from the object in an attempt to stop it

Friction is a good way to think about it Friction is a good example of this – it is a force that always acts in the opposite direction of a moving object We understand that friction causes objects to slow down because it applies a force in the opposite direction to cause it to stop But another way to look at it is because friction takes kinetic energy away from objects

Think back to the chair If we are only looking at the chair itself at the point that it is released – to the point that it slows down, we say that it has NEGATIVE work done to it

What about pushing a wall? If the object you are pushing doesn’t experience a displacement – it means that you have done no work on it Since no energy was transferred – ie. The object didn’t gain kinetic energy and didn’t move, the work is said to be zero Think about pushing on a wall: even though YOU are using energy and applying a force, that’s not getting to the wall since it doesn’t move

Power Power refers to rate of energy use – how much energy is used per second