Let's Get Physical

In this article, we'll cover:

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• Introduction to physics

• States of matter: solid, liquid and gas

• Concentration, diffusion and osmosis

• Energy

• How energy changes states of matter

• How to measure energy

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Introduction to physics

So far, we've looked at elements and atoms but from the point of view of chemistry: atoms binding with each other by sharing their electrons (it can also happen in other ways, as described in the 'Chemical Bonding' article). But there are other things that atoms can do, on their own or together with other atoms that are what we call physical interactions, rather than chemical.

Leaving behind the very tiny scale of atoms for now, we'll think about larger things. So let's go with a tennis ball.

A tennis ball is a physical object and physical interactions would include, for example, you picking up the ball, throwing the ball or hitting the ball with a racket. Describing what's happening to the ball while you perform these physical actions with it, is part of the subject of physics. If it's about physical movement, including dropping it so it falls, then it's to do with physics. Also, if you didn't like the tennis ball the way it is, you could try to cut it with a knife. If you did a good enough job of it, you could cut the ball in two. This is a physical action as well and understanding why you're able to cut a tennis ball with a knife but you can't cut through a rock, for example, would require knowledge of physics. Physics can answer questions such as "how fast does this thing move?" and "why does a ball stop moving through the air after I throw it?"

So moving objects, cutting them, crushing them or even joining them together like adding a wheel to a car or stapling paper together and how and why exactly these things happen, are all explained by having an understanding of physics.

Also included are understanding things like heat, light, sound and even electricity. Heating up water so it turns into steam, is a physical process. It's not a chemical change that happens to water as it turns into steam but a physical one. So once again, we need to learn physics to understand this.

As I wrote earlier, physics also looks at what atoms can do and this includes their component particles. So for example, how fast electrons move and where we can find them around the nucleus.

What's the matter?

Matter is all the physical stuff that exists in the universe. As you know, it comes in many different forms. Broadly speaking, we can categorise these forms into three states of matter: solid, liquid and gas. By touching each of these, you can get a good feel for what the differences are.

If you touch a liquid, such as water, you'll find your hand moves through it. That's because the molecules in a liquid are far apart enough that they move out of the way as you push your hand into it.

Solids, like a brick or a table are too hard for your hand to pass through. The atoms/molecules in a solid are too close together and don't allow things to pass easily between them.

Gases, like steam are even easier than liquids to pass your hand through. The molecules are so far apart that they will eventually get far away enough from each other that you no longer see the gas. The atoms haven't gone away: it's just that they are so spread out and because they are so small, you can't see an individual one or two of them. Hydrogen and oxygen, which we've seen before, are gases.

Concentration, diffusion and osmosis

This section is more important for chemistry rather than physics, especially in school science. However, I decided to put this in a physics article because concentration and diffusion refer to the physical quantities of atoms and molecules, as we'll see in a minute, and it's beneficial to go from learning about states of matter into this topic.

Concentration refers to the amount of atoms or molecules in a given space. It's a lot easier to see this in liquids. If you use a liquid like fruit squash (in British English, or cordial elsewhere) and pour it into a glass, you get the most concentrated squash. Fill it the whole way, so you can compare it with the other glasses we will use. Next, fill another glass, of equal size and type, half with squash and half with water. This second glass is more watery, which we call dilute. You have taken squash and diluted it down so that it's now half as concentrated as the squash in the first glass. The more squash that's in the glass, the more concentrated it is; whereas the more water, the more dilute.

We can also try pouring salt into a glass half full with water. Now, salt isn't a liquid, but the same principle applies to a load of small solid bodies as with a liquid. So again, the more salt we add to the water, the more concentrated it will be. However, as you may notice, if you use fine grains of salt, it mostly 'disappears' but if you use larger chunks of salt, like rock salt, it will fall to the bottom of the glass. Taking a spoon and mixing the salt around, will allow it to dissolve into the water. Like we saw with gases, it doesn't mean the particles have gone away, but the molecules are now in little groups or even on their own and so are too small to see. The particles of salt become evenly spaced out throughout the water. So remember to mix a solid when you do an experiment like this. The same goes for a heavy liquid, like maple syrup.

By the way, water is referred to as a solvent when other things are dissolved in it. The solid substance you put in is called a solute. The combination of solute and solvent is called a solution. There are other solvents that can be used, but we'll stick with water for now.

An important note is that water is used for making solutions but concentration refers to the other thing you add into the water, not the water itself. You can't have more concentrated water:- it's always the liquid or other thing you add to it that's referred to as having a level of concentration.

Diffusion is when matter moves from a higher concentration to a lower concentration. You'll notice as you slowly pour squash into a glass of water, the squash will spread out. This is because it is diffusing to areas where it's not as concentrated (or has no squash at all). Eventually, the squash particles will be equally distributed throughout the glass of water as long as it dissolves in it. For an example of a liquid that doesn't dissolve in water, try an oil such as sunflower oil or olive oil. As you pour it into water, it will rise to the top and make a layer on the surface.

But going back to liquids that do dissolve, imagine two containers of say, orange squash, with a divider or small wall (called a membrane) between them. This membrane has tiny holes to allow a few molecules to flow back and forth between the two containers. Now, the containers start out with different concentrations of orange squash. Let's see it:

The orange spheres represent molecules of orange squash and the blue spheres represent molecules of water. The membrane along the middle divides the containers, with the gaps representing the tiny holes. So the orange squash is more concentrated in Container 1 relative to Container 2. This means that the squash will diffuse from the first container to the second container (the molecules pass through the gaps in the membrane) until you reach what is called equilibrium: or an equal concentration between the two containers.

So the state of equilibrium for these two containers would look like this:

Osmosis is the movement of water molecules from a lower concentration to a higher concentration. So it's the reverse of diffusion. This is only because concentration doesn't refer to water, as I wrote before. You still have the same process happening with water as with other liquids, in the sense that water moves from where there are lots of water molecules to where there are less.

So in our two containers, you will get diffusion of orange squash and osmosis of water - water molecules move from container 2 into container 1, until there is a state of equilibrium.

Energy

Energy can be hard to understand if you don't have a good handle on the basics. You've probably heard adults talk about children when they're running around and jumping on things etc and say something like "they have lots of energy". This energy is something that when they have lots of it, they can move around a lot and do lots of things. When they have a little amount of energy, they cannot do as much. You'll also notice that when you have lots of energy you are able to lift and carry heavy things, but when you have very little energy, you can hardly lift anything. If you had no energy (or more likely, too little energy) you wouldn't be able to lift that heavy object at all.

So energy is the capacity to do work. You can say that something big like a human being or a truck has energy or something small like an atom or electron. It takes more energy for something to move around for longer or to move faster. It also takes more energy to lift something very heavy as opposed to something light. So a lack of energy can prevent something performing an action or causing a change on something else. If you were to chop up a potato, for example, you would need to put in more energy to cut it all the way through than to simply slice it. It's energy that makes the world go round.

Now, energy isn't a 'thing'; that is to say, it's not a substance. You wouldn't be able to hold onto a piece of energy or throw it around. It's the property that something has, which enables it to do work of some kind or other.

There are different forms of energy and they include:

Kinetic energy - this is the energy when something moves around. When an object moves faster, it has more kinetic energy. Also, if a small object and a large object were moving at the same speed, the large object would have more energy. In other words, it takes more energy to move something big.

Potential energy - this is a general term for energy when it's stored. One example of potential energy is a spring when it's taught, or wound up and takes up less space. This will make more sense when you learn more about how energy works, which we'll get to a little later.

Electrical energy - the energy that electricity has. The more energy in electricity, the more it can power something like a light bulb - a brighter light is made by electricity with more energy.

Heat energy - the more heat energy an object has, the hotter it is.

As well as heat energy, you can have light energy or sound energy or many others. I'll explain more about these types of energies on the articles about waves and electromagnetism. But don't worry about these for now, the important thing is to comprehend the idea that there are different forms of energy.

A very important rule about energy is that you can't make new amounts of energy in the universe. You can increase the amount of heat energy in a room by turning on an electrical heater or using a fireplace or central heating, but that energy has moved from whatever it is that's doing the heating into the air within the room.

Energy can be transferred or converted from one form to another. Potential energy, if it's to be used for anything useful, would need to convert or transfer into another form of energy. So I'll use the example of a spring. When it's taut, it has potential energy and then when you release it, it's converted into kinetic energy.

Mechanical energy is the combination of potential energy and kinetic energy. So for the spring, instead of saying potential and kinetic energy, depending on whether it's taut or let loose, you can just say it has mechanical energy.

A battery is another example of potential energy that is converted into a different form of energy. In this case, the battery converts potential energy into electrical energy.

Chemical energy is a type of potential energy that is stored in the bonds between atoms and molecules. The energy from these bonds are used for chemical reactions. The chemistry articles will get into this.

How energy changes states of matter

When we say that an element is a solid, liquid, or gas, we mean that this is the state of matter it becomes at room temperature (i.e. the average temperature of a room, which is 23 degrees Celcius).

If you heat up a solid enough, it will melt and become a liquid. Heat energy makes the particles (atoms or molecules) move faster, to the point that the physical state of the substance changes. Heating up a liquid enough will, you guessed it, change it into a gas.

Cooling down a gas, or in other words, removing heat energy from the gas, will change its state into a liquid. The particles slow down and move closer together. Further cooling can turn this liquid into a solid.

As an example, water is a liquid at room temperature, but at 0 degrees Celcius, it becomes a solid:- ice. When water is heated up to 100 degrees Celcius, it becomes a gas:- steam.

Elements have melting points, which is the temperature required to change its state from solid to liquid and boiling points, which is the temperature to change its state from liquid to gas.

Counting energy

To keep this section simple, I'll just say the unit of energy that is most commonly used is joule. So to measure the amount of energy something has, you would count its number of joules. The same goes for how much energy is converted or transferred.

So that's it for an introduction to physics; including matter and energy. These are very important concepts, not only in your study of physics, but in all aspects of science.