Welcome to Five Minute Science, where we offer up cool science experiments you and your kids can do together using everyday household items, in about five minutes!
This week you get to make milk swirl, and learn some science too, from the experts at Let's Talk Science.
To show what happens when you mix liquids that have different kinds of molecules.
Be sure to ask your child what he or she thinks might happen before you do the experiment – what result is expected when you place a cotton swab dipped in dish soap in the centre of a plate of milk with drops of food colouring added?
- Milk (2% or higher - the more fat the better)
- Food colouring (2-3 colours recommended)
- Dish soap (dishwashing liquid)
- A cotton swab
- A plate
- Pour milk onto a plate covering the bottom.
- Place 4-6 single drops of food colouring randomly on the surface of the milk.
- Dip the cotton swab in the dish soap and place the tip of the cotton swab in the centre of the milk. What do you see?
Explaining the Science:
Did you see the swirls of colour when you placed the cotton swab in the dish? What do you think is making the colour move around? The scientific explanation has to do with the different molecules in the two liquids -- the milk and the dish soap. Milk contains many different types of molecules, such as water, proteins and fat. Water and fat do not mix, even when they are together in milk - the fat forms little globs which are separate from the watery part of the milk. The molecules in dish soap are interesting because they are polarized - that means that each end of the molecule has an opposite reaction. One end of the dish soap molecule is attracted to water, while the other end is attracted to fat. So when the dish soap is added to the milk, the part of the molecule that is attracted to water moves towards the water in the milk and the part of the molecule that is attracted to fat moves towards the fat in the milk. This causes the turbulent, swirling reaction. The food colouring helps to show that turbulence - and looks pretty too!
This experiment is simple, safe and appropriate for any age. In the Ontario Science and Technology curriculum, Properties of Liquids and Solids is taught in Grade 2.
- Try using different types of milk (skim, 2%, homogenized). How does that affect the swirling of the colours?
- Try dipping a clean cotton swab (no dish soap) into the milk. What happens?
- Try dipping the cotton swab in other liquids (e.g. lemon juice, fizzy pop) and see what happens. Is that what you expected?