Density is one of the most useful concepts in physics...
Combined Science57 views·Updated Jun 5, 2026·4 pagesDensity Practice Questions and Detailed Answers
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Basic Density Calculations
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!
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Finding Mass from Density
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.
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Real-World Applications
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!
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Floating and Sinking
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.
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Combined Science57 views·Updated Jun 5, 2026·4 pagesDensity Practice Questions and Detailed Answers
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...
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Basic Density Calculations
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!
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of 4Sign up to see the content. It's free!
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Finding Mass from Density
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.
3
of 4Sign up to see the content. It's free!
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Real-World Applications
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!
4
of 4Sign up to see the content. It's free!
- Access to all documents
- Improve your grades
- Join milions of students
Floating and Sinking
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.
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.
Similar content
Most popular content in Biology
9Most popular content
9Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5App Store
4.7/5Google 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 SiOS 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 KlichAndroid 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.
AnnaiOS user