﻿Just take a moment to note down the date, and the title, so that you can keep your notes organised. Hi, I'm Miss Todd and I am going to be doing some lessons on the Matter topic with you. Today's lesson is going to focus on atmospheric pressure. For today's lesson, you're going to need a pen, some paper, and a calculator, as we're going to be doing some maths skills. If you don't have any of those things, can you please pause and go and get them now! Can you also make sure, that you've got a nice quiet place to work, so that you won't be distracted during today's lesson. In today's lesson we're going to look at, why the Earth and other planets have an atmosphere, changes in atmospheric pressure, and being able to calculate percentage decrease. So we'll start by looking at what causes the atmosphere. Just take a moment to look at this image. It shows the different levels of our atmosphere. The atmosphere is the name that we give, to the layer of gases that surround a planet. The Earth's atmosphere is about 700 kilometres high, and is made of different levels. Some of these levels you can see in the image. Other planets also have an atmosphere, some are much denser like Venus, and others much thinner like Mars. So why do planets have an atmosphere? Planets have gravity, and these gas molecules are held close to the surface, by this force of gravity. Bigger planets, have a bigger gravitational field strength. This means that those bigger planets, have denser atmospheres. So take a look at this image of Earth and Mars. What I would like you to do, is pause here and on your piece of paper try and explain, why Mars has a thinner atmosphere than Earth. Think about what we've just looked at, on the slide before, about gravitational field strength. Check your answers and make any changes if you need to. So Mars is smaller than Earth. Therefore, Mars has a weaker gravity. This means Mars can not hold as many gas molecules as close to the surface, like Earth can. So it has a thinner atmosphere. Pause now, if you need to make any changes. The atmosphere exerts a pressure on us all of the time. You might not have heard this word exerts before, it just means apply. So the atmosphere is applying a pressure on us, all of the time. We don't feel this pressure as our body exerts the same pressure outwards, so the forces are balanced. We can use experiments to prove the existence of atmospheric pressure.

As a demonstration of atmospheric pressure, we placed some water inside a large metal can. We've heated the water up to the boiling point, and the steam has displaced all the air in the can. We'll now tightly cap the can. The steam inside the can will condense. This will produce a very low pressure inside the can. There's atmospheric pressure on the outside the can. We'll add some cold water on top of the can. The can collapses due to the large difference in pressure.

You've just watched a video, on the collapsing can experiment. Let's just go through together, what that experiment was showing us, using a little can. To start with the pressure inside the can, is the same as the pressure outside the can. Some water is poured into the bottom of the can. The can with the water inside is then heated. As the water starts to boil, the pressure increases, because the gas molecules, are colliding with the surface of the can. Using tongs the can is put into some cold water. The pressure will now decrease, as these molecules have lost energy. They will be colliding with the can less often. The can is then crushed, because the pressure outside of the can, so the atmospheric pressure, is suddenly higher, than inside the can. Let's just have some quick questions, to test our knowledge of this experiment. So what happens to the pressure, as the can heated? Does it increase, decrease, or stay the same? Shout the answer for me! Good, it increases. What happens to the pressure, when the can is cooled? Does it increase, decrease, or stay the same? Excellent, it decreases. So if the can is crushed, what does that tell us, about the pressure outside of the can? Is it higher, lower, or the same as inside the can. Excellent, it's higher. Do here, is write down the steps of the experiment, and finish them off for me. Just pause the video and resume when your done. Good, here's the answers. Great work if you've used your knowledge of particles to explain. Can you please just pause here, and make any changes to your answers if you need to. And play when you're ready to start again. So we're going now to look at how atmospheric pressure can change. The higher the altitude, the lower the pressure. So altitude means height. So the higher you go, the less pressure there is. And this is why your ears pop on the plane. The pressure is lower when you are higher up, because there are fewer particles colliding with your ear. That means that the pressure outside of your ear, has now decreased, because the plane is at a high altitude. Therefore the pressure inside your ear, is now higher than outside. So the air in your ear, is pushing on your ear drum and your ears pop. Just pause and have a read of those if you need to. So now that we've looked at the idea of altitude, and how the pressure is lower, when you're a up high. I would like you to explain, why the aeroplane windows are so thick. So what we need to do is we need to break this down, into some smaller questions. Where is the aeroplane? What is the pressure like outside of the plane? Why? What would that mean about the pressure inside the plane? And what are these thick windows preventing? What I would like you to do, is answer each of these questions onto your piece of paper. So just pause now and play when you're ready. Good, so the plane was at a high altitude. So the pressure outside of the plane will be lower. This is because the particles in the air have more space between them, so they're colliding less. Inside the plane the pressure is higher than outside. So the thick windows will stop them exploding outwards. If you need to add anything to your answers, can you please pause now and do so. So just take a look at this image here, this is Mount Everest. Climbers have to take oxygen tanks, when they're climbing up Everest, as as they get to the higher altitudes, there is lower air pressure. This means there are less particles of oxygen, but they need to make sure that they've got enough oxygen, going into their lungs. The summit of Mount Everest is about 9,000 metres high. On Mount Everest, the water will boil at about 90 degrees rather than the usual 100 degrees. This is because bottom point decreases, as the altitude increases, because of this drop in pressure. This table shows some data, on how the boiling point changes, depending on the altitude. What I would like you to do, is look at this table and describe how the boiling point changes, with the altitude. I would then like you to try and explain, why water boils more easily at greater heights. Just pause now and resume when you're ready for the answers. Good, so we could see, as the altitude increases, the boiling point decreases. And water boils easier because the higher altitude, means lower pressure. This means less energy is needed, for the liquid water to turn into a gas, so the water will boil at a lower temperature. For this section of the lesson, you're going to need your calculator. If you don't have a calculator, you can use one on your phone, or one on your computer. Water boils at 97 degrees C, at 1,300 feet above sea level. But at Everest base camp, it boils at 82 degrees C. Calculate the percentage decrease in boiling point. So I'll do this one, so you can see how to find percentage decrease. We need to first start by finding the difference in these temperatures. So 97 minus 82 gives us a temperature difference of 15 degrees C. The equation for finding percentage difference, is the temperature difference, divided by our initial temperature, and multiplied by 100. So I can now put the values that I have into this equation. So my temperature difference was 15. We divide this by our initial temperature, which was 97. We then multiply our answer by 100. So 15 divided by 97 is 0.155 When we multiply this by 100, it gives us a percentage decrease of 15.5% Let's do this one together. Water boils at 91 degrees C at 3,500 feet above sea level. But to Everest base camp, it boils at 82 degrees C. Calculate the percentage decrease in boiling point. So what do I need to do first, shout at me! Excellent, I need to find that temperature difference. So 91 minus 82 gives me a temperature difference, of nine degrees C. I've got my equation, so what do I need to do now? Brilliant, I need to put the values that I have into this equation. So my temperature difference was nine, divide that by the initial temperature, which was 91. And then I'll multiply this by 100. So what I would like you to do, is put nine divided by 91 into your calculator. Make a note of your answer on your page. I would then like you to multiply this answer by 100. This will give you, your percentage difference. Make a note of the answer on your page. So nine divided by 91 is 0.099 When you multiply this by 100, you should have got 9.9% So well done, if you've got a percentage decrease of 9.9% This one you're going to do on your own. So water bottles at 97 degrees C at 1,300 feet above sea level. But at 3,500 feet, it boils at 91 degrees, calculate the percentage decrease in boiling point. I will put the equation on the screen for you. So pause here, and work out the percentage decrease in boiling point. Resume when you're ready for the answers. Let's go through the answer together. So you needed to start by calculating your temperature difference. So this is 97 minus 91, and that would give you a temperature difference of six degrees C. We then needed to put these values into your equation. So the temperature difference was six and divide that by 97, which is our initial temperature. That would give you an answer of 0.062 We then need to multiply this by 100. That would give you your percentage decrease of 6.2% So well done, if you've got a percentage decrease of 6.2 If you didn't, can you please pause here, and just write down these steps. So during today's lesson, we've looked at what causes the atmosphere. So planet's gravity, holds the gas molecules close to the surface, and the bigger the planet, the bigger the gravity. So they have a more dense atmosphere, cause they can hold more gas molecules, close to their surface. We've also looked at how atmospheric pressure can change. So as the altitude increases, the atmospheric pressure will decrease. This is why your ears pop on the plane, and why water boils at 90 degrees, on Mount Everest. We've also developed our math skills by being able to calculate the percentage decrease, in the boiling points at different altitudes. So that brings us to the end of today's lesson, and I hope you've enjoyed it as much as me. What I'd like you to do, is look through your notes and pick up three things that you think are important, that you've learned today. I would then like you to go and completely exit quiz. I hope you have a wonderful rest of the day.

This lesson explores phenomena of atmospheric pressure including how atmospheric pressure is caused using the particle model to deepen our understanding.

Science

Y8 Science

Key Stage 3

Year 8

Miss

Atmospheric pressure

Matter

Physics

THEME

UNIT

Particle theory

Change of state

Density

Diffusion

Pressure in liquids

Hydraulics

Floating & sinking

Robert Brown

Matter revision (Part 1)

Matter revision (Part 2)

Lesson overview: Atmospheric pressure

Intro Quiz

Video

Presentation

Worksheet

Exit Quiz

Transcript

11 lessons in Matter: