Some things sink while other things float. Why is this? Let's find out!
Watch and learn
Video
Floating and sinking
Whether and objects float or not is controlled by the Sorry, something went wrongCheck your connection, refresh the page and try again. of the object.
Density is how tightly packed the material inside something is.
For example, a sponge ball and a marble have different density. You can feel the sponge ball is less dense because you can squeeze it and change its shape.
If you put them in water, the less dense sponge ball floats, and the more dense marble sinks.
What will happen if you place a hollow golf ball and a solid golf ball in a bowl of water?
The hollow ball floats. It is full of air which is less dense than water.
The solid ball sinks. That's because the material inside is tightly-packed and more dense than water.
If something has a density that is less than the density of the water, the object will float.
And if something has a density that is greater than the density of the water, the object will sink.
Buoyancy and forces
There are two forces acting on objects in water:
鈥 the weight of the object being pulled down by gravity
- the upthrust from the water underneath the object pushing up.
If the object is less dense than water then the upthrust is greater than the weight and the object will float.
If the object is more dense than water the upthrust is less than the weight and the object will sink.
If an object floats we say that it is Sorry, something went wrongCheck your connection, refresh the page and try again..
What is buoyancy? revision-guideWhat is buoyancy?
Find out more about buoyancy.
Density and liquids
Did you know that liquids have different densities?
For example oil is less dense than water but syrup is more dense than water.
A less dense liquid will float on top of a denser liquid.
Also, salt water is denser than fresh water, so a ship will float higher in the salty sea than in the fresh water of a river.
Experiment
You can make your own experiment to explore the different densities of liquids.
You will need:
- golden syrup
- water
- cooking oil
- a tall jar
Add each liquid slowly and carefully to the jar so that don鈥檛 mix.
Which liquid is the most dense? Which liquid is the least dense?
Activity
Buoyancy isn't just about density. Shape makes a difference too as you can find out in this experiment.
Try this floating and sinking experiment!
You will need:
- Tin foil to make boats from
- A container filled with water
- Marbles or coins to act as weights
Make different shapes of boat with the tin foil. See how much weight you can add before they sink.
Watch the video to find out more.
Video
Key words
Sorry, something went wrongCheck your connection, refresh the page and try again. 鈥 How well something floats. If an object can float, we say that it is buoyant.
Sorry, something went wrongCheck your connection, refresh the page and try again. 鈥 How tightly packed the material inside something is. Objects with higher density than water will not float鈥
Quiz
Test your knowledge of buoyancy with our fun quiz!
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