Hi there, I'm Mrs. Kempe, and welcome to today's lesson about energy provided by food.

This fits into the diet and exercise unit, but you might also recognise some of the information from healthy diets back in primary school.

Okay, then let's get started.

So our outcome for today is I can calculate the amount of energy provided by different foods by measuring a change in temperature.

This is a really exciting lesson, so I can't wait to get started.

You're going to be needing some words from today, that you may not have heard of before, and they are appearing on the screen now.

If you would like to read them in more detail, please do pause the video.

Otherwise don't worry, I will be explaining them as we go through the lesson.

So we have three learning cycles today, investigating energy provided by food, collecting data, data analysis and evaluation.

And we will be starting with investigating energy provided by food.

Okay, so let's start by thinking about some foods that are a really good source of energy.

Can you have a think back to our balanced diet lesson perhaps? What kinds of foods did we talk about when we were talking about energy? Okay, did you think about things like bananas, sweet potatoes, Brazil nuts? These are foods that are really high in carbohydrates, and really high in really good fats.

They're whole foods, so they haven't been ultra processed and so actually they contain a real range of different nutrients, not just energy in the form of carbohydrates and fats, but they've also got lots of vitamins, minerals, and fibre in them that we need in order to have a healthy balance diet.

Now, if you would like to find out how much food, how much energy is in your food, then we can look on the back of food labels and we can see that the measurement of energy is actually in kilojoules or in kilocalories on there.

It's just in that circle of purple.

Obviously when we're looking at whole foods, they wouldn't have one of these information labels on the back of them, things like bananas, but you can actually look those up on the internet if you wish.

Now we can carry out a simple investigation in order to measure the amount of energy provided by different types of food.

So food scientists would be doing this in order to find out what numbers they should put on the back of these labels.

When we do this investigation, we're going to be changing some factors.

Anything that we change in an investigation, it is called a variable, okay? Variable meaning change.

So we've got three types of variables, independent variable, that is the factor that is being changed, the dependent variable, that is the factor that is being measured.

And finally, the control variable.

This is a factor that needs to be kept the same to make the investigation valid.

It's important to use that term valid for this one.

Okay, so onto our first check of the day then, this one is a true or false.

A dependent variable needs to be kept the same to make the investigation valid.

Is that true or is that false? Can you then justify your answer? A, a dependent variable is a factor that is being measured.

B, an independent variable is a factor that is being changed.

I'll give you a moment to think about it, but if you do need more time, please do pause the video.

Okay, did you choose false? Well done, that's brilliant.

And of course that is A, a dependent variable is a factor that is being measured.

Okay, fabulous, well done.

All right then, so I'm gonna tell you how we can carry out this practical.

All right, when food is burnt, the energy provided by the burning food can be used to heat some water.

You can see there the types of equipment that we're going to need for this investigation.

We'll need to be able to burn different types of food and see how much energy is being provided by heating that water and then we can measure the temperature change.

So how much that water changes from the start.

Then once we've heated it to afterwards and that difference from the starting point to the end point.

This is the equation that we're going to need in order to calculate that temperature change then.

So temperature change, which we're going to measure in degrees Celsius with a thermometer, is equal to the final temperature again, to degrees Celsius minus the initial temperature again in degrees Celsius, making sure that our unit is the same throughout.

Can we remember that, then? How do we calculate change in temperature? A, by finding the mean.

B, final temperature minus initial temperature, or C, initial temperature minus the final temperature.

I'll give you a moment to think about it, but if you need more time, please do pause the video.

Okay, of course that was B, final temperature minus the initial temperature.

I hope you've got that right, well done.

All right then, onto how to draw our table to record the results.

Now when we draw a table, we need to make sure that we put our independent variable in that first column.

Okay, so this one is our type of food.

We're then going to put our dependent variable into our next set of columns.

And this one we're going to need to be able to record the mass of the food each time.

And we also then need to have a place to record our final temperature, our initial temperature, and also that temperature change, which we will calculate at the end of the practical.

So true or false, to calculate the temperature change, we only need to know the final temperature.

Is that true or is that false, can you justify your answer? The final temperature tells us the change in temperature, or B, we need to know the initial and final temperature to calculate the change.

I will give you a moment to think about it, but if you need more time, please do pause the video.

Great, that of course is false and it's B, we need to know the initial and final temperature to calculate the change.

It's really important when you do the practical to remember to take that initial temperature.

We're now moving on to our first task of the day, task A.

Please do open up your worksheets, get them ready, so that you can record your results on there.

In this investigation, we will be burning different types of food and seeing how much energy is provided, by heating water and measuring the temperature change.

Write down for me the independent variable, the dependent variable, and the control variable for this investigation.

I will give you some time to think about it, but if you do need more time, please do pause the video.

Okay, let's have a look at those answers then.

So the independent variable would be our type of food.

The dependent variable's going to be that temperature change of the water, and our control variable would be the mass of the water, mass of the food.

That's why we need to record the mass of the food and the distance between the food and the boiling tube.

Well done.

Okay then, so we're gonna move on to our next learning cycle, which is collecting data, and hopefully you will be able to do your practical in this time in order to gather some information.

So let's have a look at what equipment we need, first of all, we're going to need a balance, because we will need to weigh the mass of our food before we start.

We will need a boiling tube to hold the water that we're going to heat.

We will need a thermometer to work out that temperature change.

We will need a mounted needle that will hold the food, a Bunsen burner in order to ignite or set fire to the food, a measuring cylinder so that we can keep the volume of the water the same each time, a heat proof mat so that we can make sure that we are working safely.

A retort stand in order to hold our equipment on.

The food there is being mounted on the needle, and a clamp that will hold our boiling tube.

So once we set up all our equipment that looks like this, then we can begin.

Now this is the method for this practical.

Number one, weigh the food sample on the balance and record the mass.

Number two, add 30 centimetres cubed of water to the boiling tube.

Number three, measure the starting temperature of the water.

Remember that's really important, using our thermometer.

Number four, hold the food sample on the mounted needle, and ignite using the Bunsen burner.

Number five, hold the burning food close to the boiling tube until it goes out.

Number six, measure the final temperature of the water.

Number seven, repeat that again from one to six and calculate the mean temperature change.

Repeat steps one to seven for different food samples.

We can actually watch a video of this demonstration.

When we're watching the video we should think about what our safety advice would be, wearing goggles 'cause we're using glassware, and also making sure that we do not touch the equipment because it will be hot.

The first thing we need to do is to light the Bunsen.

We turn the gas on, and we put the flame over the top of the Bunsen.

We take our water in our measuring cylinder, and we pour it into our boiling tube.

We then place a thermometer into the boiling tube, and wait until it has adjusted to the temperature.

We take our food sample and we weigh it on a balance.

We write that number into our data table.

We then check our thermometer, and we write that starting temperature into our table.

We then need to place the food sample onto the mounted needle.

We're going to set fire to it.

So we open the hole on our Bunsen burner and we hold the food above it.

Once it is lit, we hold it underneath our boiling tube about two to three centimetres away.

Ensure that your heat proof mat is below the food in case it drops.

Once the food has gone out, we turn off our Bunsen.

And then we wait a moment for the thermometer to stop moving.

Once it has, we take that temperature and we write it into our table.

Now we've watched that demonstration, then, let's move on to our next check of today.

This one is a true or false.

Okay, it is helpful to repeat the experiment and measurements for each food sample.

Is that true or is that false? Can you justify your answer? Doing it once for each food sample is usually enough.

B, this enables us to calculate a mean temperature change for each food sample.

I'll give you a little bit of time to think about it, but if you do need more time, please do pause the video.

Okay, did you put true? Well done.

And that is because this enables us to calculate a mean temperature change for each food sample.

So another check for us, this time we're going to have a go at calculating the temperature changed for puffed rice cereal.

So remember that equation from earlier on? I'm going to give you a moment to think about it, but if you do need more time, remember to pause the video.

Did you get 11? Excellent, well done.

Okay, onto our next practise of the day.

This is task B, and what I would like you to do is carry out that investigation if you're able to and record the results in your results table, then I'd like you to calculate the mean temperature change for each type of food, okay? Remember that we add those up, and divide by the number of samples that we take.

So if you repeated it three times, you would add those temperature changes up, and then you would divide by three.

I will give you some time to think about this, and to carry out your practical, but you will need more time.

So please do pause that video.

Okay, so I have got some practise data here for you if you are unable to carry out that practical.

So please do calculate my temperature change and the mean temperature change from here.

And this is the calculated temperature changes, and that mean temperature change for each.

So for my bread, I got 11, sorry, eight, 11, and nine.

When I added those together, and divided by three, I got 9.

3, then I added 24, 26, 28, I divided by three, and I got 26.

Please note that in that mean temperature change there, what I've got in that column is they both have the same decimal places.

So although there isn't anything after the decimal place of 26, in order for it to look right in my table, then I've put a.

0 on the end of it.

Maybe just have a quick check of your data, and make sure that you've got the same decimal places in that column.

You'll also notice that in my table I only have the units in the title of the table.

If you have put the units in the body of the table, so for instance for the bread, you've put three grammes next to that three, can you please take those out as well? 'Cause that's also incorrect.

We just want them to be in the title of the table.

Right, so onto our final learning cycle of today.

This is data analysis and evaluation.

So what we're going to do is we are going to calculate the energy provided by the food samples using an equation.

The equation that we need for this one is the energy provided by food is equal to the mass of water, times by the temperature change, and then times by 4.

2.

Energy will be measured in joules, mass of water will be in grammes, and temperature change will be in degrees Celsius.

One centimetre cubed of water is the same as one gramme of water.

Therefore because we use 30 centimetres cubed of water, then that is equal to the same as 30 grammes of water.

Just so that we know which numbers we are using.

Let's have a go at using that equation then together.

So we're going to calculate the energy provided in two grammes of food and we're going to start with puffed wheat.

Now the puffed wheat temperature change is five, okay? We used 30 grammes, remember of the water.

So it's 30 times by five, times by 4.

2, that gives us 630 joules.

However, we did actually have two grammes of that puffed wheat.

So therefore we need to find out what it is for one gramme.

So we do 630 divided by two.

That gives us 315 joules per gramme, okay? So we need to remember that.

We need to find out how much it is per gramme at the end.

Now I'd like you to have a go at this, then.

This time I'd like you to try it for the puffed rice that you can see on the screen there.

I'll give you some time to think about it, but if you do need more time, please do pause the video.

Okay, did you get 1,386 joules for the puffed rice for two grammes? And then if you remember, we then need to divide it by two because that is how much of the food we used, and it's 693 joules per gramme.

I'm sure you've got that right, well done.

Okay, now actually, why do we want to know this? What are we interested in this for? So we can compare the foods by the energy they provide per gramme.

That puffed rice actually provided more energy than the puffed wheat per gramme.

And so why would you wanna know that? The reason being is that you'd need to try to balance that with how much energy you are using in your lifestyle.

So here's a professional tennis player, he's gonna have a really active lifestyle, he's gonna be training all the time, and he's going to need a lot of energy.

So therefore he would probably want to be eating that puffed rice to make sure that he has got enough energy to carry out all his activities.

Equally, if you have someone that's very sedentary, then you would probably recommend the puffed wheat, because they're not using as much energy, and so therefore they need to make sure that they are not increasing their BMI.

All right then, if we evaluate our data, we can have a look at it more closely and see whether or not there was anything that is not necessarily expected.

So when we have completed our experiment, we want to have a little look at it and see what we can work out.

Now sometimes it might be that when you burnt that food, not all of the food actually was burnt.

Sometimes it falls off the mounted needle and you can't really get that tiny little bit back, back onto the needle in order to heat it again.

Some of the energy is actually not just heating up that boiling tube, but it is lost really, to and transferred to the surroundings and there's nothing that you can do about that with this particular type of equipment.

So onto our next check, why is the data not always what we expect? A, food labels are often incorrect.

B, not all the food is burned.

C, some of the energy is transferred to the surroundings and D, we have used different amounts of food.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, of course not all of that food is burnt, and some of the energy will be transferred to the surroundings.

Excellent, well done.

Onto our final task of the day then.

So using the data in your table, can you calculate the amount of energy provided by each of your foods, the amount of energy each of the foods provides per gramme.

Compare the different foods.

Which would you recommend in small serving sizes and why? If you didn't actually complete the investigation, please don't worry, you can use the sample data.

You will find that on your worksheet.

I would like everyone to get that out now so that you can record your answer.

If you need more time, please do pause video.

Okay, so this was my sample data from earlier that we had a look at, and these were the answers from that particular sample data.

If you're working with somebody else, it might be good to sort of swap your work now so that they can check your calculations for you.

Now, using my data, I chose the cracker contains the highest amount of energy per gramme.

You can see it's there at 2,142 joules per gramme.

The bread has the lowest energy per gramme, which is 1,008 joules.

Oh sorry, no it's not, it's 336 joules per gramme.

Foods with a high energy content should be eaten in moderation as part of a balanced diet and an active lifestyle.

Excellent, really well done.

So, when very close to the end now, I just want to go through some of the key learning points from today.

So different foods provide different amounts of energy.

We can investigate the energy provided by foods by burning them.

The burning food can be used to heat water, and the temperature change can be measured.

The amount of energy provided by each food can be calculated using the following equation.

Energy provided by food is equal to the mass of water, times by temperature change, times by 4.

2.

Each food that is tested can be repeated and a mean calculated.

The amount of energy provided by our food should be considered along with activity levels of the individual and also portion sizes.

Well done today.

It's been a really great practical to have a go at.

So I hope that you did get the opportunity.

Otherwise, I hope the video allowed you to imagine how it would've worked.

Thank you very much, hope to see you again, bye.