In this video we'll be looking at expansion and contraction, and what that looks like at a particle level in solids, liquids and gases. When heat is added to any particles their kinetic energy or their moving energy is increased. When this happens the particles move further away from each other. This happens because the molecular bonds between those particles become weaker due to the increased energy of the particles. As they move further away from each other the substance takes up more space; this is called expansion. This occurs in all states of matter, solids, liquids and gases. Now there's two things that are important to note here. Firstly, it's important to note that the size of the particles do not change - they remain exactly the same. What changes is the amount of space between those particles. The second thing to note is that this is not a chemical change, this is merely a physical change where the space between the particles has been moved further apart. The particles themselves have not changed at all, they're the same size, yes, but they are also the same substance - they have not changed into a new or different substance. When heat is removed from a substance the particles slow down and move closer together. This means the substance takes up less space; this is called contraction. Again the size of the particles do not change, it is the space between them that is now reduced. Let's look at a couple of examples. So in a solid... you might have done this experiment in school already. Here we have a metal ball and a metal ring. At room temperature the ball fits perfectly through the ring. After heating the ball however, it no longer fits through the ring. This is because the space between the solid particles have expanded and therefore take up more room, so the actual ball has expanded it won't fit through the metal ring that had not been heated. This is an important concept in real life as it impacts many design elements. For example, have you ever wondered why the sidewalk is created in separate blocks and not just one smooth line? It is to allow for expansion and contraction to occur. As the sun hits the concrete it will expand. As the sun leaves the concrete it will contract. If the gaps aren't left in between then the concrete will crack because it doesn't have enough room to allow expansion to occur and the particles have nowhere to go. This is also the case with railway tracks. Every few meters the tracks have a small break in them to allow for the expansion to occur. For liquids, probably the most common example that you would see most often is in a thermometer. When heat is added to the thermometer the liquid particles inside move around with more energy and therefore spread apart. This causes the liquid to rise in the thermometer and we can see a change in temperature. An experiment you might see in the classroom is like this one - heating some water with a thin glass tube. As you watch the thin tube you will see the water rise as more heat is added, demonstrating that the water takes up more space when the particles have more kinetic energy. For gases, an easy example to replicate at school or home is blowing up a balloon. Blow it up and tie it up and measure the circumference of the balloon. Now put it in the fridge or freezer. After 10 minutes, take it out and compare the circumference again. Now leave it out to warm back up to room temperature again. Compare it again. In this example when heat is removed by placing it in the freezer the kinetic energy of the particles is slowed down so the particles are able to move closer together and therefore they take up less space. As the particles warm up again at room temperature the balloon will re-inflate as the particles now need more room to move around. Hopefully this video has helped you to visualise what is happening at a particle level when states of matter expand and contract. If you like this video please hit like below and subscribe to my channel. Thank you!