Tag Archives: float

Brennan has enrolled in swimming classes now and is showing some interest in it – woo hoo! Being a former competition swimmer, I hope he continues but up to this point, he is pretty scared of the water.  I guess I understand for now.  While I dont know for sure, I started thinking that he was scared of sinking in the water and not coming back up.

So last night, I started trying to explain to him why he would usually float and what it takes to sink. I found an old book in our home library called Floating and Sinking. Unlike I hope you find this blog, it was very confusingly written but it did serve its purpose of putting him to sleep.  The whole time he asked many questions as to how floating and sinking worked. The easiest way to explain it for me was to say, “Things float when they are less dense than whatever they are in.” That triggered a whole discussion on density. As you have probably figured out, I think people learn best by doing – hence, this post on The Sinking Straw.

This takes about 5-10 minutes to build and is quite easy.  Here is what you need:

In case the images didn’t come up:

• 1 small rubber band
• 1 straw cut to about 4 in long
• several small paper clips (mine needed 4 but it varies)
• 1 2l bottle – like everything we do
• 1 “test vessel” which about the same height as a 2l bottle

Instructions:

1. About an inch down, wrap the half of the rubber band around the end of the straw
2. Fold the end of the straw down and wrap the rest of the rubber band around it
3. Put several small paper clips in the other end of the straw. After testing, I found I needed four. You may need more or less.



4. Now, test your straw sinker in the test vessel which is filled with water.  Drop it in and push down on the top of the sinker. If it barely floats and comes back up when you tap it – congratulations you inserted the right amount of paper clips.



5. Fill the 2L bottle with water almost to the top.
6. Drop in the sinker
7. Screw the cap on very tightly so water doesn’t spray everywhere.



8. When you squeeze the bottle, the sinker should drop.  When you let of the pressure, the sinker should go back to the top. It’s a gift that keeps on giving with every squeeze!

Why does this work?

Magic of course.  Or … Squeezing the bottle reduces the amount of space that the air can take but the water takes up the same amount of space so some water goes up in the straw.  The water in the straw makes it heavier. Since the straw’s volume didnt change it is more dense and so it sinks.

Brennan’s video play by play:

Dana