Have you ever noticed that you can hold some of your drink in a straw if you put your thumb (or your tongue!) over the end? Then watch it come careening out when you let go? Kinda fun, huh?
What keeps the liquid in the straw? Well, when you cap a straw full of liquid with your thumb, you stop any air at the top from coming in or going out. Even though gravity is tugging on the liquid to fall out, it's prevented from dropping. If you let go, the air pressure from outside the straw can expand into the straw and the liquid pours out.
Let's put this fun science trick into use with an experiment! In this month's 20 Minute Lab, we'll hold a "rainbow" in a straw, using common items from home, while exploring the concept of density!
LET'S GET STARTED!
Check out the video to see how it worked for us!
Why did the colored water without salt all mix together? Why did it stay in nice rainbow layers with the salt? The answer has to do with density, or how much 'stuff' can be packed into a given space.
The first experiment you did - with just water and no salt - is called a control. A control is when you do an experiment where nothing interesting is added or changed. We wanted to see what would happen without the salt. The water all had the same density - just a cup of water and 8 drops of food coloring. The same amount of 'stuff' in each one!
When the density is the same, there's nothing to prevent the water from mixing in the straw and the colors getting muddled.
An experiment with a variable is when you add or change something to see what happens. In this experiment, salt is the variable. The different amounts of salt means that each container had a different amount of 'stuff' in it. Some with a little salt, some with a lot. In other words, each container had a different density.
More dense liquids sink. The first thing you added to the straw was the purple water - the one with the least salt and therefore, the least dense. Then you sucked up some blue, the next least dense - but more dense than the purple - which stayed happily below the less dense purple water. All the way to red, the most dense solution. They don't mix because their densities keep them stacked in their places!
Try starting from red (most dense) and going to purple (least dense) instead - what happens?SHARE WITH US!
Let us know how your experiments turned out! Share your photos and results with us on Facebook, Twitter, Instagram, or send us an email to email@example.com. We love getting your messages!
For more exciting experiments, check out our Yellow Scope science kits on the Shop tab of our website!