Let me first introduce myself. I am a mother of 6 year old very energetic twin boys and started this as an attempt to make kids interested in science. To make them understand density I made a simple coloured rainbow with liquids in a small glass with the materials available in my kitchen. The result was as shown below and the kids loved it
Lets first do the experiment and then talk about the physics behind it. here is the list of the materials that I used
Oil ( any cooking oil can be used)
water + food colour
If you don’t want to use these the same experiment can be done making the sugar solutions with different food colours.
The sequence was
Pour honey first, then liquid soap, after that I poured coloured water, then pour oil and finally the rubbing alcohol.
you can pour in different order as well but the liquids will settle down as shown below. Enjoy your colourful creation without disturbing it.
The end result is the picture that I posted on top. Now let’s understand why it happens? However before we do so lets also see what happens when we throw a straw in the bucket of water and when we throw a stone in the bucket of water. The stone sinks because it is heavier than water but straw floats because it is lighter than water. The same principle applies here..Honey is heavy so it settles in the bottom whereas alcohol is the lightest so it comes to the top.
Another concept that is very closely related to the concept of density is the concept of mass and weight.
Do you know what is the difference between Mass and Weight?
If you ask this question to people the common answer that you will get is that they are the same. However they are not..though these are closely related with each other.Weight is a force which is felt as we experience the gravitational pull and will change if we go to the moon or to the outer space whereas the Mass is something that will remain constant wherever you go.
Which is heavier 1 Kg of iron or 1kg of feathers?
Did you fall for that and said Iron? Both are 1 Kg and hence weigh the same but you will need a lot of feathers to make it as equal to 1 Kg of iron.
Lets also find out what happens if we put 1kg of iron bars and 1 kg of feathers in two boxes? which box will be heavy to lift? Of course the one with the iron bars in it. The same volume of feathers will be much lighter as feathers are not as dense as iron . Mass is actually how much stuff is actually there in a thing. So now we can define density as the amount of mass in a specified space.
The unit of density is Rho and is arrived at dividing the mass of an object by the volume
Density = Mass/Volume
The standard measuring unit for the same is kilogram per cubic meter. This is so that when scientists are talking to each other they can understand and relate to each others discoveries.
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