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Erin Wilson
07/12/2025
Physics
Topic 3 - Particle Model of Matter
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7 Dec 2025
•
Understanding the Particle Model of Matter - Topic 3
Erin Wilson
@ezpez06
1 / 5
Understanding Density and States of Matter
Density is basically how tightly packed the particles in a substance are - think of it as measuring how "squashed together" everything is. Dense materials like lead have particles crammed close together, whilst less dense materials like foam have particles spread out with lots of gaps.
The density formula is straightforward: Density = mass ÷ volume . This means if you compress something into a smaller space, it becomes denser because the mass stays the same but the volume shrinks.
Solids are the densest because particles are locked in fixed positions with strong forces holding them together - they can only vibrate on the spot. Liquids are less dense since particles can slide past each other, even though they're still close together. Gases are usually the least dense because particles zoom around freely with almost no forces between them.
Quick Tip: Remember that ice is unusual - it's actually less dense than liquid water, which is why it floats!
Measuring Density in the Lab
Regular solids are dead easy - just weigh them, measure length × width × height for volume, then use your density equation. Job done!
Irregular solids need the displacement trick. You'll use a eureka can filled to the spout, then drop your object in. The water that overflows into your measuring cylinder tells you the object's volume - clever, right?
Liquids require a bit more patience. Zero your balance with an empty measuring cylinder, then add 10ml at a time, recording the mass each time. Calculate density for each measurement, then find the average for accuracy.
Lab Hack: Always take multiple readings and average them out - it makes your results much more reliable and shows examiners you understand experimental accuracy!
Changes of State and Internal Energy
Changes of state are physical changes, not chemical ones - this means you can always reverse them and get back exactly what you started with. The particles don't disappear or change; they just rearrange themselves differently.
Internal energy is the total energy stored by all the particles in a system, including their movement energy (kinetic) and position energy (potential). When you heat something, you're adding energy to this internal store.
Temperature rises when particles move faster, but during melting or boiling, the temperature stays constant even though you're still adding energy. This energy goes into breaking the bonds between particles instead of speeding them up.
The opposite happens during freezing or condensing - particles form new bonds and release energy, but temperature stays steady until the change is complete.
Memory Aid: Think of it like a crowded dance floor - particles need energy to break free from their partners (change state) before they can dance faster (increase temperature)!
Specific Latent Heat
Latent heat is the energy needed to change state without changing temperature - it's the "hidden" energy that goes into breaking or forming bonds between particles.
Specific latent heat tells you exactly how much energy you need to change 1kg of a substance from one state to another. Different materials need different amounts of energy, which explains why some things melt or boil much more easily than others.
There are two types you need to know: specific latent heat of fusion (solid ↔ liquid changes) and specific latent heat of vaporisation (liquid ↔ gas changes). The equation is simple: Energy = mass × specific latent heat.
This explains those flat bits on heating and cooling graphs - the temperature stays constant whilst all the energy goes into changing state rather than changing temperature.
Real-World Example: This is why sweating cools you down - your body heat provides the latent heat of vaporisation to turn sweat into water vapour!
Particle Motion and Gas Pressure
Gas particles are like tiny bouncing balls, constantly moving in random directions at different speeds. When you heat a gas, you're giving these particles more energy, so they move faster on average.
Temperature is directly linked to the average kinetic energy of the particles - higher temperature means faster-moving particles. Since kinetic energy depends on speed squared (½mv²), even small temperature increases make a big difference to particle speed.
Pressure happens when these speedy particles bash into container walls. More collisions or harder collisions both increase pressure. Heat up a gas and particles move faster, creating more force when they hit the walls.
The pressure-volume relationship is inversely proportional: if you squash a gas into half the space, you double the pressure (assuming temperature stays constant). The rule is: pressure × volume = constant.
Safety Note: This explains why aerosol cans warn against heating - higher temperature means higher pressure, which could cause the can to explode!
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Basil
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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
Understanding the Particle Model of Matter - Topic 3
Erin Wilson
@ezpez06
Ever wondered why ice floats on water or how a thermometer works? It all comes down to density and particle behaviour! Understanding how particles move and arrange themselves helps explain everything from why gases expand when heated to how we... Show more
Understanding Density and States of Matter
Density is basically how tightly packed the particles in a substance are - think of it as measuring how "squashed together" everything is. Dense materials like lead have particles crammed close together, whilst less dense materials like foam have particles spread out with lots of gaps.
The density formula is straightforward: Density = mass ÷ volume . This means if you compress something into a smaller space, it becomes denser because the mass stays the same but the volume shrinks.
Solids are the densest because particles are locked in fixed positions with strong forces holding them together - they can only vibrate on the spot. Liquids are less dense since particles can slide past each other, even though they're still close together. Gases are usually the least dense because particles zoom around freely with almost no forces between them.
Quick Tip: Remember that ice is unusual - it's actually less dense than liquid water, which is why it floats!
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Measuring Density in the Lab
Regular solids are dead easy - just weigh them, measure length × width × height for volume, then use your density equation. Job done!
Irregular solids need the displacement trick. You'll use a eureka can filled to the spout, then drop your object in. The water that overflows into your measuring cylinder tells you the object's volume - clever, right?
Liquids require a bit more patience. Zero your balance with an empty measuring cylinder, then add 10ml at a time, recording the mass each time. Calculate density for each measurement, then find the average for accuracy.
Lab Hack: Always take multiple readings and average them out - it makes your results much more reliable and shows examiners you understand experimental accuracy!
Sign up to see the contentIt's free!
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 and Internal Energy
Changes of state are physical changes, not chemical ones - this means you can always reverse them and get back exactly what you started with. The particles don't disappear or change; they just rearrange themselves differently.
Internal energy is the total energy stored by all the particles in a system, including their movement energy (kinetic) and position energy (potential). When you heat something, you're adding energy to this internal store.
Temperature rises when particles move faster, but during melting or boiling, the temperature stays constant even though you're still adding energy. This energy goes into breaking the bonds between particles instead of speeding them up.
The opposite happens during freezing or condensing - particles form new bonds and release energy, but temperature stays steady until the change is complete.
Memory Aid: Think of it like a crowded dance floor - particles need energy to break free from their partners (change state) before they can dance faster (increase temperature)!
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Specific Latent Heat
Latent heat is the energy needed to change state without changing temperature - it's the "hidden" energy that goes into breaking or forming bonds between particles.
Specific latent heat tells you exactly how much energy you need to change 1kg of a substance from one state to another. Different materials need different amounts of energy, which explains why some things melt or boil much more easily than others.
There are two types you need to know: specific latent heat of fusion (solid ↔ liquid changes) and specific latent heat of vaporisation (liquid ↔ gas changes). The equation is simple: Energy = mass × specific latent heat.
This explains those flat bits on heating and cooling graphs - the temperature stays constant whilst all the energy goes into changing state rather than changing temperature.
Real-World Example: This is why sweating cools you down - your body heat provides the latent heat of vaporisation to turn sweat into water vapour!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Particle Motion and Gas Pressure
Gas particles are like tiny bouncing balls, constantly moving in random directions at different speeds. When you heat a gas, you're giving these particles more energy, so they move faster on average.
Temperature is directly linked to the average kinetic energy of the particles - higher temperature means faster-moving particles. Since kinetic energy depends on speed squared (½mv²), even small temperature increases make a big difference to particle speed.
Pressure happens when these speedy particles bash into container walls. More collisions or harder collisions both increase pressure. Heat up a gas and particles move faster, creating more force when they hit the walls.
The pressure-volume relationship is inversely proportional: if you squash a gas into half the space, you double the pressure (assuming temperature stays constant). The rule is: pressure × volume = constant.
Safety Note: This explains why aerosol cans warn against heating - higher temperature means higher pressure, which could cause the can to explode!
We thought you’d never ask...
What is the Knowunity AI companion?
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.
Where can I download the Knowunity app?
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Is Knowunity really free of charge?
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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
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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