Hello there.

My name's Mr. Forbes.

And welcome to this lesson in the Hidden Forces unit.

It's called Stretching Springs.

In the lesson, you're gonna be carrying out an experiment to find out what happens to a spring when you put different forces on it and how that affects its length.

By the end of this lesson, you will have carried out an experiment where you put weights on the end of a spring and you measure how much that spring extends and the different weights around it.

And hopefully you'll have found a pattern in the behaviour of the spring.

So when you're ready, let's start.

And here's the set of keywords that you'll need to understand in the lesson.

The first of them is extension.

And in physics we use the word extension to mean the additional length of something, so you'll be measuring the extension of the spring as it gets longer.

Gravitational force is the force that pulls things downwards.

Hanging masses are small round discs of metal that we use to produce those forces.

And a mass hanger is something that we put those masses on.

And this is the set of definitions for those keywords and you can refer back to it during the lesson at any time.

The lesson's in just two parts.

And in the first part, I'll explain how you can carry out the experiment before you carry out yourself.

And then in the second part, we'll look at your data and see how accurate it is and how you could make it more accurate in the future.

So let's get on with the first part, measuring the extension of the spring.

So if you have a spring and you put a force on it, then the coils in that spring, the little hoops will become further apart and the spring will get longer.

We say that the spring has extended, so putting a force on it causes an extension and that extension is just the increase in length of the spring.

If you put a larger force on it, then it's gonna extend further.

The coils are gonna move further apart and it gets longer still, so you've got a larger extension.

Let's have a look at some stretching of spring.

Putting a force on the spring will make those coils separate out just like this.

You pull again and they'll still separate and pulling harder will make 'em separate more.

Okay, and you saw in that video that when the force was put on the spring, the coils moved further apart and it stretched.

Now in the video, you saw there was an uncontrolled force acting on the spring, so it was impossible to measure it.

In our experiment, we need a controlled force.

So to create a controlled force, we're going to stretch a spring by putting masses on the end of a hanger.

The mass hanger is gonna have 100 gramme masses on it and each of those is going to pull down with a force of one Newton.

So here I've got a spring and I've put a mass holder on it and there's a one newton force pulling down, making that spring longer.

If I add 100 gramme mass to it, then there's gonna be a greater force and the spring will extend a bit more.

Adding more masses will cause that force to increase and so the spring will get longer and longer still.

You can see the pattern there.

So the purpose of the lesson is to see if there's a relationship between the force you put on the spring and the extension of it.

You've already seen that the spring gets longer, but is there an actual pattern in the behaviour that we can analyse in detail? So putting the masses on will create that extension.

We'll measure that and then we'll put more masses on and measure the new extension and see if there's a relationship between the force pulling downwards and the extension of the spring.

This is the equipment you're gonna use for the experiment.

You can see here it's a few stands, a ruler, a spring, and some masses.

So going round, you'll hang the spring from the clamp stand as shown in the diagram here.

You then align a ruler, and it's important to get this ruler vertical and you'll put that so that the zero on the ruler is exactly level with the bottom of the spring.

So just the, and that's one of the most important parts of the experiment, making sure that those two things line up: the zero on the ruler and the very bottom of the spring.

Okay, it's time for our first check and what I'd like you to do is have a look at the simple diagram here and decide what's wrong with it.

Is it A, the spring is not vertical, B, the ruler is not vertical, C, the end of the spring and the zero on the ruler are not in line? So pause the video and make your selection and then restart.

Okay, you should've selected the ruler's not vertical.

You can see quite clearly that the ruler is tilted to the side there, and that wouldn't be very good for this experiment.

Well done if you got that.

Now as I've mentioned, it's very important that we line up the equipment properly in this experiment.

And to do that, there's two possible pieces of equipment we could use.

We can use a ruler or a set square.

So you can position a ruler like this holding it so that it's in line with the bottom of the spring and checking that it lines up with zero on the other ruler or you can use a set square like this.

So a set square's got that right angle in it and that allows you to align it with the ruler as well.

Now if possible, you've gotta really concentrate on keeping that ruler horizontal so it's not tilted, otherwise you'll read the wrong measurement off the other ruler.

And that's where a set square becomes more important because it's easier to keep the set square horizontal, 'cause you can line it up with that vertical ruler.

And that means that you'll be able to make more accurate measurements if you've got a set square.

So if you've got one, use one if possible.

Okay, another check now.

I'd like you to look at this equipment and decide what's wrong with it.

Is it A, the spring is not vertical, B, the ruler's not vertical, or C, the end of the spring and the zero of the ruler are not in line? Pause the video, make your choice and then restart.

Welcome back, and the answer to that one was it's not at zero.

You can see clearly there that the bottom of the spring is at the 1.

5 centimetre mark.

Well done if you got that.

So once you've aligned the equipment properly, you can put the mass hanger on the end of the spring and the mass hanger produces a downward force of one newton, so what's gonna happen to the spring is it's going to stretch.

If you use the set square, then you get an accurate measurement of how much that spring has stretched or extended.

And so you can just look at the reading on the ruler and you can see there that that spring is extended down to the three centimetre mark.

It's got three centimetres longer, so its extension is three centimetres.

Right, to check if you can measure an extension of a spring, I've got a diagram here.

I'd like you to look at the diagram and decide what's the extension of that spring.

So pause the video and then restart when you're ready.

Okay, your answer should have been 7.

5 centimetres.

That's where the bottom of the spring is on the ruler, So my set square allows me to read that easily.

Well done if you've got that.

So to continue the experiment, you add 100 gramme masses to the mass holder one at a time and measure the extensions.

So you can see there I've added another hundred grammes, that's producing an extra force, and so the spring is extended a bit more.

I measure that extension by putting the set square or ruler against the first vertical ruler and you can see there I've got an extension of six centimetres.

You can continue to do that, adding more masses on recording the different extensions in the table like this.

Once you've added five masses, producing a total downwards force of six newtons, you can stop.

You don't wanna overextend the spring.

And the next stage is gradually taking those masses off one at a time and recording the extension in the second column of your results table here.

So you're going to put masses on all the way down to six newtons and then take all those masses off.

Okay, I'd like to check if you understand the stages of the experiment now.

So I've got the stages, but they're not in the correct order though.

I've labelled them A, B, C, and D.

All I'd like you to do is to write down the letters in the correct order please.

So pause the video, make your selections, and then restart.

Welcome back, the correct order for this is D, set up the equipment with zero on the ruler in line with the bottom of the spring.

A, hang a mass hanger on the spring and measure the extension.

C, add masses one at a time and measure the extension for the spring for each.

And then B, remove the masses one at a time and measure the extension of the spring each time.

Well done if you've got that order.

Okay, it's time for you to carry out the experiment now.

I've written down the stages that you have to follow here and we can watch a brief video that shows you all of those stages.

So let's watch that video now.

(plastic rattles) (metal scratches) (plastic scratches) (plastic rattles) (metal scratches) (metal clanging) (plastic scratches) (plastic thuds) (plastic rattles) (plastic rattles) (metal scratches) (metal clanging) (metal rattles) (metal clanging) (plastic scratches) (plastic rattles) (metal rattles) (metal clanging) (plastic scratches) (metal clanging) (plastic scratches) (metal scratching) (metal rattling) (plastic scratches) (plastic rattles) (metal scratches) (metal rattles) (plastic scratches) (plastic rattles) (metal clanging) (metal scratches) (metal rattles) (plastic scratches) (metal scratches) (metal rattling) (plastic scratches) (metal scratches) (metal rattling) (plastic scratches) (metal rattling) (plastic rattling) Hopefully that was helpful.

You can always look at the video again if you get confused at any point.

So I'd like you to go through these stages and collect your data in a table, please.

So pause the video, take your time to carry out the experiment, and then restart, and we'll look at some results.

Welcome back, here's a set of results I've collected in the test experiment.

And as you can see, I've got the loading extensions and the unloading extensions all collected there.

Your results will be different, because you'll have used a different spring, but your general pattern should be the same.

You can see there's an increase in the extension with the force and then when you take those weights back off again, it decreases again, so the extension returns back to zero.

Well if you've got a set of results that looks something like this.

Right, we're ready to move on to the second part of the lesson now, and this is just a short part where we'll look at our results and see if they're accurate and how we could've made them more accurate.

So let's go and do that.

Scientists use diagrams of equipment rather than photographs because diagrams make things clear.

The diagrams allow us to see how things set up and how they're related to each other and they're much easier to understand than a photograph.

So for example, this is a photograph of the equipment that you used and this is a diagram of it.

And the diagram is much clearer, showing how the rulers match against each other.

And we can add labels to that diagram a little bit more easily than we could add labels to the photograph.

So diagrams are much more useful for scientists as they allow us to see things much more clearly.

The diagrams are also more useful, because it's easier to mark on it how we make measurements.

So I've got my diagram of the experiment here and you can see the two stands, the spring, the mass holder, and the set square.

And the set square here is what's the important thing because that's the measuring instrument we're using.

We're putting that against the ruler and it allows us to measure the extension.

And in the diagram, I can quite easily mark where the extension is.

It's from the top of the ruler where the zero is to the top of that set square.

So that diagram has made it much easier for me to show how to measure the extension, where the extension is.

Okay, so here's another diagram, but this diagram's got a mistake on it.

So what I'd like you to do is to decide what mistake has the pupil made according to the diagram.

So is it the ruler's not positioned, so at the end of the spring was at zero? Is it the set square is not level and so will not give accurate readings? Or is it the extension is being measured from the top of the spring? So pause the video, make your selection, and then restart.

Okay, hopefully you spotted that one fairly quickly.

The student's not measuring the extension correctly.

They should be measuring it from the zero on the ruler.

Not from the top of the spring because that would also involve the length of the spring.

And that's not what we're measuring.

So we'll done if you spotted that.

Now one of the reasons that you carry out the experiment by adding weights to the spring and measuring its extension and then taking the weights off again and measuring the extension is we can compare the loading data they're putting the weights on and the unloading data to see if the patterns match across them.

And that will give us some indication whether or not the measurements have been made accurately or not.

So you can see in this table, the two sets of data match fairly closely.

So there's only small differences between them.

So you can see for force of one newton, the extension varied slightly, but we can say that those two sets match pretty closely.

So I'm fairly happy that those measurements have been made accurately.

Let's check if you understood what I meant by that.

So I've got three tables of data here and I'd like you to look carefully at them and decide which of those sets of data seems to have been measured most accurately.

So pause the video, make your selection, and then restart.

Okay, looking at the data, you should've noticed that one of the tables of results has results that match each other much more closely than the other two.

And that was A.

So if you selected A, well done.

That's the most accurate set of data.

Right, we're on to the final task of the lesson now, and I've got a diagram here that's partially completed.

What I'd like you to do is to complete and label that scientific diagram to show how you could accurately measure the extension of the spring when there's a mass hung on it.

Then I'd like you to explain why taking two sets of measurements helps to check that the accurate readings have been taken during the experiment.

Okay, so pause the video and work on those two tasks and restart once you've got your answers.

Okay, welcome back and this is what your diagram should look like.

I've labelled the parts, the spring, clamp stand, mass holder, mass, ruler, and set square.

The important part there was the measurement of the extension.

So you should've included that set square and marked clearly where the extension was measured from, the zero on the ruler to the top of the set square.

Or if you didn't have a set square, a ruler as well, a horizon ruler.

So well done if you did that.

And your explanation.

And your explanation about why we need two sets of data should be something like this.

You can look at the two sets of data and see if they're very similar.

That'll help show that you may have taken some accurate results.

Well done if you've got that.

Okay, we've reached the end of the lesson now, and this a summary of what you should have found.

A spring extends when a force pulls on it.

So putting that force on it makes it gets longer.

The extension is an increase in the length of the spring.

And the greater the force you put on it, the bigger the extension.

So when you put more weights on there, the spring got longer and longer.

You should also understand that we use scientific diagrams to show how the equipment's set up, but also to show how we take measurements and make those accurate.

Well, that's the end of the lesson.

Hopefully I'll see you in the next one, goodbye.