Which force acts downwards on an object with mass?

Which force slows a parachute down?

Which force acts in the same direction as the movement of a car?

What is the independent variable?

What is the dependent variable?

What is the control variable?

What was the conclusion to our investigation?

Why does the area of the parachute affect the drop time?

Investigating Speed

﻿Hello, everyone. I'm Mrs. Wolstenholme. And welcome to this lesson. In this lesson, we're going to be discussing something called drag, how we can reduce drag and also friction. All you need for this lesson is a pen and a piece of paper. So please pause the video to go and get those. I hope you've managed to get those and you're ready to go. We need to make sure that we can really focus on what we're going to be learning. So let's go somewhere that's quiet where we're not going to get distracted and let's turn our mobile phone off or put it on silent. Once we've done that, we'll get going. Let's start with what drag is. We've already learned about three forces that act in the opposite direction to the motion of an object. Here are three pictures and each one is representing one of those forces. See if you can guess which one is which. Pause the video to have a go. Here are the answers. The cyclist is moving through the air. So there is air resistance. Little girl is sliding down the snow. So there is friction And the polar bear is trying to move through water. So there is water resistance. Really well done If you remember it. Two of these, air resistance and water resistance come under the sort of category of drag. So drag is the force that's opposite to the motion and it is in liquids or in gases. So air resistance and water resistance are both drag. Here is the spacecraft, Endeavour. It had orbited the earth for 10 days and it was coming back into land. As it came, it deployed something called a drag chute, which really just looks like a parachute, doesn't it? Now what this did was it increased the drag or the air resistance on the spacecraft so that it would slow down faster. And that meant that it was safer. Some liquids have larger drag than others. For example, which would be more difficult to swim in, honey or water? Honey would be much harder to swim in. Can you imagine trying to swim through honey be very difficult. So that means that there's a larger drag when you're swimming through honey than when you're swimming through water Let's do a quick summary. Friction, air resistance and water resistance all act in the opposite direction to the motion. But air resistance and water resistance are called drag. So there's my drag. That is my motion. They're in opposite directions The large of a drag, the smaller the motion. Now let summarise with some multiple choice questions. Which of these forces always act in the opposite direction to movement? Five seconds. The answer is air resistance. Really well done if you got that right. Which of these forces always act in the opposite direction to movement? Five seconds. The answer is water resistance. Really well done if you got that one. Which of the states of matter does drag act in? Five seconds. The answer is liquid and gas. Excellent job if you remember that one. There is no air in space, we call it a vacuum. Is there drag in space? Five seconds. The answer is no. If there's no air or liquid in space then there can't be any drag. Excellent job if you figured that one out. Now let's do an independent task. Here are three questions for you to answer. Please pause the video to complete your task. Well done if you tried your best and took your time. Let's have a look at the answers. Here they are. Please pause the video to check your answers carefully. Really well done if you checked your answers carefully. And now you know where you went wrong and how you'll get it right next time. Now let's talk about reducing drag. We know that drag reduces the speed or slows objects down. And there are some situations where we want to go really fast. We also know from the previous lesson that the area of an object will affect the air resistance or the drag on that object. And so the larger the area, the more air molecules that are that will get it and the larger the air resistance or the drag. So what we can do is try and reduce that area. For example, in a formula one car, look how low they are to the ground. They're very thin. They have a small area. And this whole thing is so that they reduce drag. When something is designed in such a way to reduce drag we say that it is streamlined. So streamlined means that it is designed in such a way that it can reduce drag. Another example is cycling. When cyclists are trying to go really fast, they crouched down. This reduces the area that is being hit by those air molecules. And it reduces the drag. Let's summarise this. When the cyclist crouches down, they have a smaller area. This means the cyclist is more streamlined. This will decrease the air resistance and the cyclist can travel faster. The same can be true of fish. Lots of fish have very thin, that's because when they're swimming they want to reduce the drag or the water resistance. And so to do that, they have a very thin face so that's the area that's hitting the water head-on is very small. And that will reduce the drag or the water resistance. So we can say that fish are streamlined. Now it's your turn. Concorde was the fastest passenger plane. How did the design help? Use the picture to fill in the gaps? Please pause the video to try this task. Well done, if you tried your best. Here are the answers. Please pause the video to check your answers carefully. Really well done. So the front of the plane had a small area, and that meant that the plane was more streamlined and it reduced the air resistance so the plane could travel faster. And we're going to use this same structure to answer the next question. This is a high-speed train. How does the front of the train help? First, try to do this completely independently. Please pause the video to have a go. If you are stack, here's some more help. Really well done If you tried your best. Please now pause the video and check your answers carefully. Again, the area of the train is very small so that it is streamlined, which will decrease the air resistance and the train can travel faster. If you said drag instead of air resistance, that's absolutely fine. Well done. So really well done to everyone who tried their best even if they found it difficult. Now let's talk about friction. We've already seen friction when two objects that are solids are trying to slide over each other. There is going to be friction. So in this case, the box is trying to slide over the ground. And there will be friction in the opposite direction to the movement. We can also see friction when we rub our hands together. It's not perfectly smooth. And it feels like there's a force pushing my hand back. And that is friction. Even hough friction can be a little bit annoying because it slows things down, we do also need friction. When we light a match much it's friction that causes the heat and for the match to light. And that's why the side of the much box is rough. It's not a nice smooth box. If you feel it, it feels quite rough, and that's to increase friction. Cars also use friction. Let's see how. This car wheel is turning in this direction. On the floor, the part of the tyre is turning in this direction. The direction of the arrow. So if the tyre is moving that way, friction's going to act the other way on the tyre. And what that does is that friction force is actually what pushes the car forwards. So the friction is opposite to the direction of the actual tyre. And that is why the car moves forwards. Now let's zoom in a little bit. I've got two surfaces here. One's moving to the right and one's moving to the left. Let's look at the bottom surface. The bottom surface is trying to move to the left but it's not completely smooth. And some of the bits that are sticking out of it are actually being pushed to the right. So as we can see, there's a force to the right which is the opposite direction it's trying to move because it is not completely smooth. This has happened all the way a lot. And overall, all these little forces in the opposite direction together cause friction. Again, this only happens when the surface is rough. Because if it was completely smooth there wouldn't be those bits sticking out. So there would be nothing to push it back. There's a picture of a road. The road is rough. It's not completely smooth. And that means that there will be friction, which is good. If there wasn't any friction on the car tyres or on the people's shoes, as they walk then everyone would slip everywhere. Ice is smoother. So here's a picture of an icy road. Now, if someone tried to walk on this road or if a car tried to drive down, it would be really dangerous because it's so smooth that there's not very much friction. And that means that it might slip and maybe even crash. Or a person who was walking might fall over because there's not enough friction. Let's now summarise this with some questions. Which of these forces always act in the opposite direction to movement? Five seconds. The answer is friction. What type of surface will have a large friction? Five seconds. The answer is a rough surface. Really well done. Which type of surface will have a small friction? Five seconds. The answer is a smooth surface. Excellent job if we got those right. Try and fill in this gap. You don't need to write it down. Just say out loud in five seconds. Ice is smooth so the friction will be small. Excellent job if you said smooth. Which of these surfaces is smooth? Five seconds. The answer is the one on the right. Well done if he said that. Which of these surfaces will have a smaller friction? Five seconds. The answer is the one on the right. So the smoother surface will have smaller friction. Excellent job if you got that right. Here our two questions for you to answer. Please pause the video to complete your tasks. Excellent job if you tried your best. All you to say was rough and smooth. Really well done, if you got that right. Or if you know what you did wrong and you know you'll get it right next time Sometimes objects are designed with friction in mind. For example, this is a winter tyre. It is designed to that it is rough. This will increase the friction. So the tyre is less likely to skid. Here are some trainers. The sole of the trainer is designed to be rough. This also increases the friction. So that, first of all, you don't skid, and also so that you can push off more easily. Now it's your turn to answer the question. Why are slides smooth? Here are two questions to help you structure your answer. Please pause the video and have a go at this. Well done if you tried your best. Here are the answers. Please pause the video so you can check your answers really carefully. Excellent job. So we want friction to be low so that we can go faster. We don't want to be slowed down by friction. And so, because the slide is smooth, that means there will be less friction or the friction force will be smaller. Excellent job if you tried your best at least. Here's another one for you to try. Why is the surface of the treadmill rough? So when I'm running on a treadmill, why is this sort of ground that I'm running on rough? Pause the video and have a go at this one. If you're struggling, here are two questions to help you Really well done if you tried your best. Here's the answer. Please pause the video so you can check your answer really carefully. Excellent job. So in this case we want the friction to be high, so we don't slip. And that means that it needs to be rough because a rough surface has a higher friction. Excellent job for getting all the way to the end of this lesson. You did so well and worked so hard. I'm really impressed. I hope that you enjoyed it and that you learned a lot. Why don't you go and do the exit quiz now so that you can show how much you've learnt. I hope that I see you in the next lesson too.

What is another word for air resistance?

Which of these is what we call drag in a specific liquid?

There is no air in space. Is there air resistance in space?

Why do cyclists crouch down?

Which forces are smaller when an object is more streamlined?

Friction is larger when a surface is ...................

Friction is smaller when a surface is ...................

If the resultant force is zero, what happens to the speed and direction of an object?

Factors that affect speed

Describe how different factors affect speed

Apply knowledge of resistive forces to explain design modifications

In this lesson we will discuss the effect of frictional forces on speed and how design features can reduce these forces.

Science

Y7 Science

Key Stage 3

Year 7

Forces and motion

Physics

THEME

UNIT

What are Forces?

Representing Forces

Resultant forces

Gravity

Weight

Avicenna and the story of inertia

Pressure

Calculating speed using an equation

Distance: Time graphs

Calculating speed using distance time graphs

Revision (Part 1)

Revision (Part 2)

Which of these is true of non contact-forces?

Which of these is a contact force?

Which unit do we measure force in ?

Which force is an upward push of water on an object?

Which force slows objects down as they slide past each other?

Which force slows objects down as they travel through a liquid?

What is mass measured in?

Gravity is a force that acts on any object with .....

What piece of equipment do I use to measure weight?

If an object is stationary the forces are ..........

If an object is moving at a constant speed the forces are ..........

If an object is accelerating the forces are ..........

If an object is changing direction the forces are ..........

If a force is spread out over a smaller area, the pressure is ........

The smaller the area, the _________ the pressure.

The larger the force, the _________ the pressure.

Which of these is a unit for pressure?

In a distance-time graph,  what does the steepest line represent?

In a distance-time graph,  what speed does a flat horizontal line represent?

If I travel 5 m in 2 s, what is my speed?

Change 3000 g to a mass in kg

Use the equation W = m x g to calculate the weight of a 30 kg dog on a planet with a gravitational field strength of 3 N/kg

Which of these is the correct equation for speed?

In the equation W = m x g, what does g stand for?

What is the unit of weight?

Why do planets have different gravitational field strengths?

If forces on an object are balanced, what will happen to its speed?

If forces on an object are balanced, what will happen to its direction?

A person rides a bike at a constant speed in a straight line. What can we say about the forces?

A person accelerates as they ride a bike in a straight line. What can we say about the forces?

If forces are balanced, what is the resultant force?

Lesson overview:Factors that affect speed

Forces and motion: