This week, as part of our ongoing STEM series, we have Liz Kelly who leads our Materials Engineering team. In her job, it’s critical to understand the properties of all materials that we want to put together in our hyperloop system – especially because our pods travel in an environment akin to flying 200,000 feet above sea level. To demonstrate the importance of material properties, she created a short experiment you can try at home.
Want to see for yourself?
Here’s what you’ll need:
- Food coloring
- Oil (canola, vegetable, etc.)
- Fizzing tablets (like Alka Seltzer)
- Small and large glass cup
- Put of water in a small cup, filling it halfway
- Add a few drops of your favorite color of food coloring
- Fill a larger cup ~¾ full of oil
- Pour the colored water into the glass of oil, leaving 1-2 inches from the top of the glass
- Adults only – cut the Alka Seltzer tab into a few small pieces
- Drop the small pieces into your cup
- Watch the magic (and science!) unfold
How it works:
There are two key scientific properties behind this experiment: density and polarity.
Density is the measure of the mass per unit volume, or how much of a material will fit into a certain space. Water is heavier than oil (when comparing equal volumes), because water molecules are packed more tightly than oil. This is why the oil stays above the water – it’s less dense. It’s also why oil floats to the top of the ocean in an oil spill.
Polarity is the way in which atoms bond with each other – it’s what prevents the oil and water from mixing. Water molecules are what we call polar because they have a lopsided electrical charge that attracts other atoms (i.e. other water molecules). This is similar to a magnet where north poles are attracted to south poles. The positive end of a water molecule will connect with the negative end of another molecule. Oil molecules on the other hand are non-polar, meaning they have no positive or negative charge, so they are not attracted to the water molecules at all.
Why does the food coloring only color the water and not the oil? The food coloring is water-based, so its molecules will remain separate as well.
When we added the Alka Seltzer tablet, it reacted with water to produce carbon dioxide gas bubbles. These bubbles are less dense than oil. They float to the top and take some of the water with them. Once at the surface, the gas bubbles pop and escape into the air. After a brief period of flight, the water sinks back to the bottom of the glass again.
Given these properties, what other liquids in your kitchen might work to make a lava lamp? What combinations of liquids work, and which ones don't? Can you figure out why?
If you can, you might be the next hyperloop materials engineer!