D for Density
A quick, 2-minute demonstration of the science of density with things available at home. And, expect kids to explore dropping random objects and some mess!
Tips to introduce
- Children who haven’t been introduced to the term density need to be demonstrated about mass, volume, and how it relates to density. You can begin with dropping random objects in a jar of water to check if each floats or sinks.
- You may want to allow them for a few days to play with water and objects on their own.
- When you think they are ready for the density experiment, write down on a sheet the things you’ll need and direct them to collect it all at one place. You can use food colors if you want the experiment to be more colorful. Fix a time and place and let them know you’ll meet them there, then.
- When you are at the experiment venue, explain to them what you are going to do without revealing what you are likely to observe.
- Set it up and let them observe what happens!
- Allow them to explain their inference if it is of their interest. Don’t push or annoyingly try to bring explanations out of them. Most importantly, enjoy if their rationales are not logical or correct. They are still children, and being right is not as important as being interested to observe and have fun with science. And then follow their cues to build on.
Things you’ll need
How do you do it?
1. Add dish wash liquid to a transparent plastic cup or a glass (1/4th can do). If you think the dish wash is getting wasted, don’t worry, after the experiment is done, you can carefully remove the other liquids and separate out the dish wash for use.
2. Tilt the cup slightly and add cooking oil along the inner wall of the cup. You can use any kind of oil. If you don’t like wasting things, you can reuse oil that remains after frying but clear without particles in it.
3. Tilt the cup slightly and add water along the inner wall of the cup. You can add a food color to water before adding if you want the density experiment to be more colorful.
4. Observe what happens.
5. You will be able to observe three distinct layers – the dish water at the bottom, the water in the middle, and the oil on the top.
6. Trying dropping in small objects like a bottle cap, lego blocks, a grape, etc. from the top of the liquids and observe where each settles down.
The Science behind
Children can tend to assume density as the mass of an object. However, it is important to make them differentiate between mass and density by introducing the concept of mass of an object in a given volume or space. Mass refers to the amount of matter contained in an object. Volume refers to the amount of space the matter in the object would occupy. For example, let’s take a small cup and a big cup and fill both with sand up to the top. Which one do you think will have higher mass? Of course, the big one. Which one will occupy higher volume? The big one again, because more the sand, more will be the space it is spread out to.
Now, do you think the ratio between the mass of the sand and volume it occupied will be the same or different for the two cups of sand? Let’s do some simple math! Let’s assume the small cup is of 50 mL capacity and we filled it with 100g of sand. The big cup is of 100 mL capacity, which is double the size of the small cup, and can hence fill in 200 g (double again) of sand. Though the mass and volume of sand in the two cups are not the same, the ratio between their masses and volumes (that is, 50/100 and 100/200 = 1/2) remains the same. And, this is the ‘density’ of the substance. In other words, how much space a substance takes up in relation to the amount of matter contained in it is density and it always remains the same.
Coming back to the density experiment, dish water is the most dense of the three liquids and hence settles at the bottom. That is, the particles in the dish wash when added to the cup, packs themselves very tightly and tends to stay at the bottom. Water has the next lower density and remains in the middle. Oil has the lowest density of the three, that is, the particles in oil tend to pack themselves relatively loose and stays on the top.
Objects dropped in the cup settled at different layers depending on their densities. A marble is more dense than the dish wash and hence sank to the bottom. The wool after soaking up in the oil became more dense than oil and hence sinks to the bottom of oil but floats on top of the water layer because it is less dense than water. The bottle cap is less dense than oil and hence floats on the top.
You can also try doing a 7-layer or a 9-layer density experiment with more liquids.
Share your experience
Was the density experiment cool? Was it fun? Did you try? Did it work? Or didn’t? Leave a word in the comment section. I would love to hear!
Here’s the full list of DIY Science Experiments in this series:
A for Air – Does Air has Weight?
B for Buoyancy – Can Egg float on Salt Water?
C for Capillary action – Rainbow Walking
D for Density – 3 Layer Density Experiment
E for Earth & Moon – Why does the Moon change its shape?: Phases of the Moon
F for Fire – Does Fire need Oxygen to Burn?
G for Gravity – Defying Gravity