Ever wondered why massive ships float whilst rocks sink? Archimedes'... Show more
Physics
Chemistry
English Literature
Biology
SociologySign 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
181
•
12 Jan 2026
•
Understanding Archimedes' Principle: Buoyancy Made Easy
Ummi
@ummi_.com
1 / 6
Understanding Archimedes' Principle
Picture yourself jumping into a pool - you immediately feel lighter, right? That's Archimedes' Principle in action! This ancient Greek discovery states that any object submerged in a fluid experiences an upward buoyant force equal to the weight of fluid it pushes aside.
Think of it this way: when you get into a bath, the water level rises because you're displacing water. The weight of that displaced water creates an upward push on your body - that's the buoyant force making you feel weightless underwater.
The science behind this is brilliant yet simple. Fluids exert pressure on all sides of submerged objects, but there's more pressure at the bottom than the top due to the fluid's weight above. This pressure difference creates the upward force we call buoyancy.
Key Insight: The buoyant force doesn't depend on the object's weight - only on how much fluid it displaces!
The Maths Behind Buoyancy
Don't worry - the formula for buoyant force is surprisingly straightforward! It's simply: F = ρVg, where ρ (rho) is the fluid's density, V is the displaced volume, and g is gravity's acceleration .
Let's break this down with a real example. Imagine a 0.5 m³ wooden block underwater. Using water's density , the calculation becomes: F = 1000 × 0.5 × 9.8 = 4900 N upward force. That's roughly equivalent to lifting 500 kg!
This formula explains why ships work brilliantly. A 1000 kg boat needs exactly 1 m³ of displaced water to float because that volume of water weighs exactly 1000 kg, perfectly balancing the boat's weight.
Exam Tip: Remember that volume (V) refers to displaced fluid, not the object's total volume!
Why Things Float or Sink
Whether something floats depends entirely on a density battle between object and fluid. If the object's average density is less than the fluid's density, congratulations - you've got a floater! If it's denser, down it goes.
Boats demonstrate this perfectly. They're made of steel (much denser than water), yet they float because their hollow design creates a huge volume with relatively little mass. The boat's overall density becomes less than water's density.
Submarines cleverly exploit this principle by controlling their density. They pump water into special tanks to become denser and sink, then pump it out to become less dense and rise. It's like having adjustable density on demand!
Hot air balloons work similarly but with gases. Hot air is less dense than cold air, so heating the air inside creates enough buoyant force to lift the entire balloon system skyward.
Cool Fact: A hydrometer uses Archimedes' Principle to measure liquid density - it floats higher in denser liquids!
Factors That Affect Buoyancy
Three main factors control how much buoyant force acts on submerged objects, and understanding these will make you a buoyancy expert. First, fluid density matters enormously - denser fluids create stronger upward forces, which explains why floating feels easier in the Dead Sea than your local pool.
Volume displacement is equally crucial. The more fluid an object pushes aside, the greater the buoyant force becomes. This is why ships are designed with wide hulls rather than narrow ones - maximum water displacement equals maximum floating power.
Object shape also plays a role, though it's trickier to calculate. A sphere and a cube with identical volumes will displace the same amount of fluid when fully submerged, creating equal buoyant forces. However, shape affects how objects move through fluids and how they orient themselves when floating.
Study Hack: For exam calculations, focus on density and volume - shape effects are usually negligible in basic problems!
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?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Most popular content in Physics
Most popular content
Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.9/5
App Store
4.8/5
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 Knowunity AI. 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 Knowunity AI. 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 Archimedes' Principle: Buoyancy Made Easy
Ummi
@ummi_.com
Ever wondered why massive ships float whilst rocks sink? Archimedes' Principleholds the answer! This fundamental physics concept explains the mysterious upward force that acts on everything submerged in fluids, from your body in a swimming pool to submarines navigating... Show more
Understanding Archimedes' Principle
Picture yourself jumping into a pool - you immediately feel lighter, right? That's Archimedes' Principle in action! This ancient Greek discovery states that any object submerged in a fluid experiences an upward buoyant force equal to the weight of fluid it pushes aside.
Think of it this way: when you get into a bath, the water level rises because you're displacing water. The weight of that displaced water creates an upward push on your body - that's the buoyant force making you feel weightless underwater.
The science behind this is brilliant yet simple. Fluids exert pressure on all sides of submerged objects, but there's more pressure at the bottom than the top due to the fluid's weight above. This pressure difference creates the upward force we call buoyancy.
Key Insight: The buoyant force doesn't depend on the object's weight - only on how much fluid it displaces!
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
The Maths Behind Buoyancy
Don't worry - the formula for buoyant force is surprisingly straightforward! It's simply: F = ρVg, where ρ (rho) is the fluid's density, V is the displaced volume, and g is gravity's acceleration .
Let's break this down with a real example. Imagine a 0.5 m³ wooden block underwater. Using water's density , the calculation becomes: F = 1000 × 0.5 × 9.8 = 4900 N upward force. That's roughly equivalent to lifting 500 kg!
This formula explains why ships work brilliantly. A 1000 kg boat needs exactly 1 m³ of displaced water to float because that volume of water weighs exactly 1000 kg, perfectly balancing the boat's weight.
Exam Tip: Remember that volume (V) refers to displaced fluid, not the object's total volume!
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
Why Things Float or Sink
Whether something floats depends entirely on a density battle between object and fluid. If the object's average density is less than the fluid's density, congratulations - you've got a floater! If it's denser, down it goes.
Boats demonstrate this perfectly. They're made of steel (much denser than water), yet they float because their hollow design creates a huge volume with relatively little mass. The boat's overall density becomes less than water's density.
Submarines cleverly exploit this principle by controlling their density. They pump water into special tanks to become denser and sink, then pump it out to become less dense and rise. It's like having adjustable density on demand!
Hot air balloons work similarly but with gases. Hot air is less dense than cold air, so heating the air inside creates enough buoyant force to lift the entire balloon system skyward.
Cool Fact: A hydrometer uses Archimedes' Principle to measure liquid density - it floats higher in denser liquids!
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
Factors That Affect Buoyancy
Three main factors control how much buoyant force acts on submerged objects, and understanding these will make you a buoyancy expert. First, fluid density matters enormously - denser fluids create stronger upward forces, which explains why floating feels easier in the Dead Sea than your local pool.
Volume displacement is equally crucial. The more fluid an object pushes aside, the greater the buoyant force becomes. This is why ships are designed with wide hulls rather than narrow ones - maximum water displacement equals maximum floating power.
Object shape also plays a role, though it's trickier to calculate. A sphere and a cube with identical volumes will displace the same amount of fluid when fully submerged, creating equal buoyant forces. However, shape affects how objects move through fluids and how they orient themselves when floating.
Study Hack: For exam calculations, focus on density and volume - shape effects are usually negligible in basic problems!
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
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
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?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
4
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Mock Exam
Quiz
Flashcards
Essay
Most popular content in Physics
Most popular content
Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.9/5
App Store
4.8/5
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 Knowunity AI. 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 Knowunity AI. 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