- Age:4+
- Time:10 min
- Difficulty:Easy
- Mess level:Low
- Supervision:Yes
The Science Behind the Orange Density Experiment
Buoyancy - the strange sounding term - is the property of an object that describes how will it behave in the liquid. In other words, it tells us will it float (it’s positively buoyant) or sink (negatively buoyant).
So why do some objects sink and others float? We could intuitively say that mass of an object plays a crucial part - heavier the object is more likely it is to sink. Not necessarily! Mass is indeed important, but it’s only one part of the story. Another important factor is a volume of an object, how big object is. Having mass and volume, we can then calculate the density of an object. Density means how tightly is the object “packed”, how much mass is there per unit of volume.
The density of an object is an actual key to understanding its buoyancy. When we put an object in the liquid it sinks until it displaces (pushes out) amount of liquid equal to its own mass. That’s actually called Archimedes' principle. It states that:
A body immersed in a fluid is pushed up by a force equal to the weight of the displaced fluid.
Another important consideration is the density of the liquid we are putting an object in. Water has a density of 1g/cm³, so the mass of displaced water is equal to its volume.
Let’s say we have an object with a mass of 10g. That means it will displace 10g of water or (since the density of the water is 1g/cm³) volume of 10cm³. So our object needs to have a volume larger than 10cm³ for it to float. In other words, if the object has less density than the water(1g/cm³) it will float. To conclude, will the object sink or float depends on the density of an object and the density of a liquid its placed in.
Buoyancy at work: an object floats if it is less dense than the water it displaces.
The object will float when its weight is less than or equal to the buoyancy force.
What will happen to the orange after you peel it?
Make your prediction, then tap an answer to check!
Floating and Sinking Oranges
So how that explains our experiment? Well, unpeeled orange floats in the water. That means that it has a density smaller than 1g/cm³. When we peel off the skin, we remove some mass, but what did we do to its volume?
Skin of an orange is full of tiny pores full of air that makes it more voluminous. After peeling the orange, we have lowered both mass and volume. But the volume is now much smaller. If we remember the density formula (mass/volume), that means the density is now larger. It’s larger than the density of the water and - it sinks!
Materials Needed for the Orange Experiment
Two oranges and a container of water: the simplest density demonstration.
Materials needed for the density demonstration with an orange.
- Water
- Bowl
- Orange (or two)
- Knife
Instructions for the Orange Density Experiment
For step-by-step instructions on how to conduct this experiment watch the video on the beginning of the article or continue reading...
👨👧 Adult supervision needed
If you use a knife to score the peel, let an adult handle it - though little hands can usually peel the orange just fine on their own. Everything else is completely safe and mess-free.
- Pour the water into the bowl
- Put unpeeled orange in. Check if it’s floating!
- Peel off the orange and try it again. Is it floating?
What Will You Develop and Learn
- What is density
- Which properties determine will the object sink or float
- Archimedes Principle
- How to use the scientific method
Key takeaways
- Buoyancy decides whether an object floats or sinks in a liquid.
- What matters is density - how much mass is packed into a given volume - not weight alone.
- An object floats if it is less dense than the liquid; water's density is 1 g/cm³.
- Archimedes' principle: a submerged object is pushed up by a force equal to the weight of the water it displaces.
- An unpeeled orange floats because its air-filled skin adds volume; peeling removes that volume, so it sinks.
Frequently Asked Questions
Why does an unpeeled orange float but a peeled one sinks?
The orange's skin is spongy and full of tiny air pockets, which give the whole orange a large volume and low density, so it floats. Peeling removes a little mass but a lot of volume, making the orange denser than water, so the peeled orange sinks.
What is density in simple terms?
Density is how much mass is packed into a given amount of space (volume). You calculate it as mass divided by volume. Two objects can be the same size but have very different densities depending on how tightly packed their material is.
What is buoyancy?
Buoyancy is the upward push a liquid exerts on an object placed in it. If that upward force is greater than or equal to the object's weight, the object floats; if it's less, the object sinks.
What is Archimedes' principle?
Archimedes' principle states that a body immersed in a fluid is pushed up by a force equal to the weight of the fluid it displaces. It explains why objects less dense than water float, they displace enough water to support their own weight.
Does a heavier object always sink?
No. Whether something sinks depends on density, not weight alone. A huge steel ship floats while a tiny pebble sinks, because the ship's shape spreads its mass over a large volume, making it less dense than water overall.
Is the orange density experiment safe for kids?
Yes, it's one of the safest experiments around. The orange can usually be peeled by hand, and if a knife is used to score the skin, an adult should handle that part. The rest is just dropping the orange in water and watching.
If you liked this experiment and want more cool stuff to do, try another kitchen experiment! Have some gummy bears around? Try Demonstration of osmosis with gummy bears. Or see what happens when you put an egg in the vinegar. Spoiler: It’s bouncy and glowing egg!
Also, you can check this interesting video from Ted-Ed that further explains Archimedes Principle and Buoyancy:
