Maths
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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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Britain & the wider world: 1745 -1901
1l the quest for political stability: germany, 1871-1991
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
Show all topics
Physics
9 Dec 2025
444
3 pages
AK Squad @aksquad_hoka
Ever wondered why ice floats on water or why a balloon pops when it gets too hot? It's... Show more
Density is basically how tightly packed particles are in a material - think of it as how much stuff you can cram into a space. You calculate it using the formula density = mass ÷ volume.
In solids, particles are like people squashed together in a packed lift - they're held close by strong forces and can only vibrate in place. This tight packing usually makes solids the densest state of matter.
Liquids have weaker forces between particles, so they're like people at a crowded party who can move around each other but stay close together. They form irregular arrangements and are typically less dense than solids.
Gases have almost no forces holding particles together - imagine people running freely around a massive field. The particles zip about at high speeds with loads of space between them, making gases much less dense.
Top Tip When measuring density in practicals, remember that irregular objects need the water displacement method (eureka can), whilst regular objects just need length × width × height calculations.
Changes of state are physical changes - like when ice melts or water boils - and they're completely reversible. The key ones are melting, freezing, boiling, condensing, and sublimating (when solids go straight to gas, like dry ice).
Here's the crucial bit during any change of state, mass is always conserved - you don't lose or gain particles, they just rearrange themselves.
Internal energy is all the energy stored by particles in a system - both their movement energy (kinetic) and the energy from their positions (potential). When you heat something, you're pumping energy into these particles.
Specific heat capacity tells you how much energy you need to raise 1kg of a substance by 1°C. The formula is ΔE = mcΔθ. Different materials need different amounts of energy - water needs loads, which is why it takes ages to heat up.
Specific latent heat is the energy needed to change 1kg of a substance's state without changing temperature. It's why ice at 0°C feels different from water at 0°C - the particles have different energy levels.
Remember Latent heat of fusion = solid to liquid, latent heat of vaporisation = liquid to gas.
Gas particles are like tiny bouncy balls constantly smashing into everything around them at mental speeds. The faster they move, the hotter the gas feels - temperature is directly linked to how energetic these particles are.
Pressure happens when these speedy particles bash into container walls. More collisions or faster-moving particles both create higher pressure - it's like being pelted with tennis balls versus ping pong balls.
Here's where it gets interesting if you heat a gas in a fixed container, the particles speed up and hit the walls harder, increasing pressure. But if you give the same gas more space to move around, there are fewer wall collisions, so pressure drops.
This gives us a brilliant relationship pressure × volume = constant (for a fixed amount of gas at constant temperature). Squash a gas into half the space, and the pressure doubles - that's why balloons pop when squeezed too hard.
When you compress a gas, you're doing work on it, which increases its internal energy and usually its temperature too. This is why a bicycle pump gets warm when you're inflating tyres.
Key Point Pressure and volume are inversely proportional - when one goes up, the other comes down, assuming everything else stays the same.
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.
12
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the fundamentals of the particle model of matter with this comprehensive booklet. It covers key concepts such as density, phase changes, energy transfers, and the properties of solids, liquids, and gases. Ideal for students preparing for AQA Physics exams, this resource includes past paper questions and mark schemes to help identify and improve weak areas in understanding. Enhance your grasp of thermal energy transfers, gas laws, and measurement systems.
PhysicsExplore key concepts in physics related to matter and energy, including atomic models, buoyancy, pressure, and heat transfer. This summary covers essential topics such as density, specific heat capacity, and phase changes, providing a comprehensive overview for students studying P1. Ideal for exam preparation and quick revision.
PhysicsQuotes from every main character
English LiteratureApp 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
AK Squad
@aksquad_hoka
Ever wondered why ice floats on water or why a balloon pops when it gets too hot? It's all down to how tiny particles behave in different materials. Understanding the particle model helps explain everything from why solids are usually... 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 basically how tightly packed particles are in a material - think of it as how much stuff you can cram into a space. You calculate it using the formula: density = mass ÷ volume.
In solids, particles are like people squashed together in a packed lift - they're held close by strong forces and can only vibrate in place. This tight packing usually makes solids the densest state of matter.
Liquids have weaker forces between particles, so they're like people at a crowded party who can move around each other but stay close together. They form irregular arrangements and are typically less dense than solids.
Gases have almost no forces holding particles together - imagine people running freely around a massive field. The particles zip about at high speeds with loads of space between them, making gases much less dense.
Top Tip: When measuring density in practicals, remember that irregular objects need the water displacement method (eureka can), whilst regular objects just need length × width × height calculations.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Changes of state are physical changes - like when ice melts or water boils - and they're completely reversible. The key ones are melting, freezing, boiling, condensing, and sublimating (when solids go straight to gas, like dry ice).
Here's the crucial bit: during any change of state, mass is always conserved - you don't lose or gain particles, they just rearrange themselves.
Internal energy is all the energy stored by particles in a system - both their movement energy (kinetic) and the energy from their positions (potential). When you heat something, you're pumping energy into these particles.
Specific heat capacity tells you how much energy you need to raise 1kg of a substance by 1°C. The formula is: ΔE = mcΔθ. Different materials need different amounts of energy - water needs loads, which is why it takes ages to heat up.
Specific latent heat is the energy needed to change 1kg of a substance's state without changing temperature. It's why ice at 0°C feels different from water at 0°C - the particles have different energy levels.
Remember: Latent heat of fusion = solid to liquid, latent heat of vaporisation = liquid to gas.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Gas particles are like tiny bouncy balls constantly smashing into everything around them at mental speeds. The faster they move, the hotter the gas feels - temperature is directly linked to how energetic these particles are.
Pressure happens when these speedy particles bash into container walls. More collisions or faster-moving particles both create higher pressure - it's like being pelted with tennis balls versus ping pong balls.
Here's where it gets interesting: if you heat a gas in a fixed container, the particles speed up and hit the walls harder, increasing pressure. But if you give the same gas more space to move around, there are fewer wall collisions, so pressure drops.
This gives us a brilliant relationship: pressure × volume = constant (for a fixed amount of gas at constant temperature). Squash a gas into half the space, and the pressure doubles - that's why balloons pop when squeezed too hard.
When you compress a gas, you're doing work on it, which increases its internal energy and usually its temperature too. This is why a bicycle pump gets warm when you're inflating tyres.
Key Point: Pressure and volume are inversely proportional - when one goes up, the other comes down, assuming everything else stays the same.
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.
12
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the fundamentals of the particle model of matter with this comprehensive booklet. It covers key concepts such as density, phase changes, energy transfers, and the properties of solids, liquids, and gases. Ideal for students preparing for AQA Physics exams, this resource includes past paper questions and mark schemes to help identify and improve weak areas in understanding. Enhance your grasp of thermal energy transfers, gas laws, and measurement systems.
PhysicsExplore key concepts in physics related to matter and energy, including atomic models, buoyancy, pressure, and heat transfer. This summary covers essential topics such as density, specific heat capacity, and phase changes, providing a comprehensive overview for students studying P1. Ideal for exam preparation and quick revision.
PhysicsQuotes from every main character
English LiteratureApp 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
Sociology