Subjects
Maths
Biology
Chemistry
English Language
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Responding to change (a2 only)
Infection and response
Homeostasis and response
Energy transfers (a2 only)
Cell biology
Organisms respond to changes in their internal and external environments (a-level only)
Biological molecules
Organisation
Substance exchange
Bioenergetics
Genetic information & variation
Inheritance, variation and evolution
Genetics & ecosystems (a2 only)
Ecology
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1l the quest for political stability: germany, 1871-1991
Britain & the wider world: 1745 -1901
The cold war
Inter-war germany
Medieval period: 1066 -1509
2d religious conflict and the church in england, c1529-c1570
2o democracy and nazism: germany, 1918-1945
1f industrialisation and the people: britain, c1783-1885
1c the tudors: england, 1485-1603
2m wars and welfare: britain in transition, 1906-1957
World war two & the holocaust
2n revolution and dictatorship: russia, 1917-1953
2s the making of modern britain, 1951-2007
World war one
Britain: 1509 -1745
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Combined Science
3 Dec 2025
54
4 pages
Los @los
Density is one of the most useful concepts in physics - it helps explain why ice floats, how... Show more
Density is simply how much mass is packed into a given volume - think of it as how "heavy" something feels for its size. The formula is straightforward density = mass ÷ volume.
When tackling density problems, always start by writing down what you know and what you're looking for. Then convert your units carefully - you'll usually work with either grams and cm³ or kilograms and m³, but stick to one system throughout.
The key trick is remembering your conversions 1 litre = 1000 ml = 1000 cm³, and 1 kg = 1000 g. Get these right, and the rest becomes much easier.
Quick Tip Always check your units match before plugging numbers into the formula - mixed units are the biggest source of errors in density calculations!
Sometimes you'll need to find mass instead of density, which means rearranging the formula. Don't panic - it's just basic algebra! If density = mass ÷ volume, then mass = density × volume.
The process stays the same write down what you know, calculate any missing values (like volume from dimensions), then substitute into your rearranged formula. Remember that volume of a rectangular block is length × width × height.
Always double-check your final answer makes sense. A small wooden block shouldn't weigh 20 kg, and a tennis ball shouldn't have the same density as lead!
Study Smart Practice rearranging the density formula until it becomes automatic - you'll use this skill in chemistry and other physics topics too.
Density is brilliant for identifying materials - that's how the miner can tell real gold from fool's gold . Even if the sample isn't perfectly pure, densities that are much closer to the real thing usually indicate authenticity.
Different states of matter have different densities too. Molten iron is less dense than solid iron , which explains why it expands when heated and contracts when cooling.
Water displacement is a clever way to measure volume of irregular objects. When something displaces 300 cm³ of water, that's exactly the volume of the object - no complicated measuring required!
Real Life This is exactly how archaeologists test whether ancient artifacts are made from the materials they claim to be!
Objects float when their density is less than the liquid they're in - that's why ice floats on water . This principle helps you solve tricky problems about boats, fish tanks, and floating objects.
When calculating maximum loads, remember to add up all the masses involved. A 1 kg fish tank plus 15.54 kg of water equals 16.54 kg total - too heavy for a shelf that only holds 16 kg!
For objects that start floating but gradually fill with water, calculate how much extra mass they can take before their overall density reaches 1.0 g/cm³. Once they hit that magic number, down they go!
Physics Fact This is why damaged ships eventually sink - as water fills the hull, the ship's average density increases until it exceeds that of seawater.
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
0
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Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Learn about the organization and properties of elements in the modern periodic table, from metals to nonmetals and their unique characteristics.
ChemistryThis is about the atomic theory of matter.
ChemistryExploring the electron configurations and valence electrons of various elements in the periodic table.
ChemistryThis is about basic concepts in chemistry.
ChemistryThese A-Level Chemistry notes are designed to provide a thorough and in-depth understanding of the key concepts, principles, and theories that form the foundation of chemistry. Developed with the goal of assisting students in their A-Level studies, these
ChemistryLearn about the importance of peptide bonds and protein structure in building and shaping proteins. And in addition, how sturctures like enzymes are important to our systems.
ChemistryApp Store
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Los
@los
Density is one of the most useful concepts in physics - it helps explain why ice floats, how ships stay afloat, and even how miners identify real gold! Understanding density calculations will give you the tools to solve loads of... Show more
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Density is simply how much mass is packed into a given volume - think of it as how "heavy" something feels for its size. The formula is straightforward: density = mass ÷ volume.
When tackling density problems, always start by writing down what you know and what you're looking for. Then convert your units carefully - you'll usually work with either grams and cm³ or kilograms and m³, but stick to one system throughout.
The key trick is remembering your conversions: 1 litre = 1000 ml = 1000 cm³, and 1 kg = 1000 g. Get these right, and the rest becomes much easier.
Quick Tip: Always check your units match before plugging numbers into the formula - mixed units are the biggest source of errors in density calculations!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Sometimes you'll need to find mass instead of density, which means rearranging the formula. Don't panic - it's just basic algebra! If density = mass ÷ volume, then mass = density × volume.
The process stays the same: write down what you know, calculate any missing values (like volume from dimensions), then substitute into your rearranged formula. Remember that volume of a rectangular block is length × width × height.
Always double-check your final answer makes sense. A small wooden block shouldn't weigh 20 kg, and a tennis ball shouldn't have the same density as lead!
Study Smart: Practice rearranging the density formula until it becomes automatic - you'll use this skill in chemistry and other physics topics too.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Density is brilliant for identifying materials - that's how the miner can tell real gold from fool's gold . Even if the sample isn't perfectly pure, densities that are much closer to the real thing usually indicate authenticity.
Different states of matter have different densities too. Molten iron is less dense than solid iron , which explains why it expands when heated and contracts when cooling.
Water displacement is a clever way to measure volume of irregular objects. When something displaces 300 cm³ of water, that's exactly the volume of the object - no complicated measuring required!
Real Life: This is exactly how archaeologists test whether ancient artifacts are made from the materials they claim to be!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Objects float when their density is less than the liquid they're in - that's why ice floats on water . This principle helps you solve tricky problems about boats, fish tanks, and floating objects.
When calculating maximum loads, remember to add up all the masses involved. A 1 kg fish tank plus 15.54 kg of water equals 16.54 kg total - too heavy for a shelf that only holds 16 kg!
For objects that start floating but gradually fill with water, calculate how much extra mass they can take before their overall density reaches 1.0 g/cm³. Once they hit that magic number, down they go!
Physics Fact: This is why damaged ships eventually sink - as water fills the hull, the ship's average density increases until it exceeds that of seawater.
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
0
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Learn about the organization and properties of elements in the modern periodic table, from metals to nonmetals and their unique characteristics.
ChemistryThis is about the atomic theory of matter.
ChemistryExploring the electron configurations and valence electrons of various elements in the periodic table.
ChemistryThis is about basic concepts in chemistry.
ChemistryThese A-Level Chemistry notes are designed to provide a thorough and in-depth understanding of the key concepts, principles, and theories that form the foundation of chemistry. Developed with the goal of assisting students in their A-Level studies, these
ChemistryLearn about the importance of peptide bonds and protein structure in building and shaping proteins. And in addition, how sturctures like enzymes are important to our systems.
ChemistryApp Store
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
