A pet peeve of mine are books on handcrafts or experiments or any kind of activity that come with drawings instead of pictures, because I always suspect that it was easier to draw whatever the author wanted to show than to take a photo of it. Which, to me, suggests that it isn’t really all that easy to conduct the experiment or build the wicker basket or whatever it is you are attempting to do.
So here is an experiment that I had seen drawings of and that Martin and I went to try: on swimming and sinking.
Step 1: Take two identical pieces of tin foil.
Step 2: Build a boat out of one of the pieces, and a ball out of the other one.
Step 3: Place the boat and the ball on the water surface.
Step 4 to step 9: (And these are the steps that the nicely drawn instructions always omit) Watch the ball float on the surface. With growing annoyance, try to make the ball as compact as possible in order to make it sink.
Step 10: This is what we wanted to see after step 3 already. Even though the boat and the ball are made of identical pieces of tin foil and their mass is the same, the boat floats while the ball sinks.
What do we learn from this? Always test experiments before using them as a demonstration, especially those that look extremely simple!
I really like hydrostatics. Of course I like moving water even better, but even static water is great. And there are so many things to explore! If I was to teach hydrostatics any time soon, there are so many little teasers I would use.
For example this one:
A sailor is standing on the bottom step of a rope ladder, painting the outside of his ship. The bottom step is 50 cm above the water, the distance between steps is 30 cm. The flood is coming in, and the water is expected to rise by 1.5 m. How many steps will the sailor have to climb in order to keep his feet dry?
Or this one:
How much heavier will a trough in a ship lift get when a ship is inside?
A: the weight of the ship
B: the weight of all parts of the ship above the water line
C: not at all
D: I don’t know*
You might think that these are really easy questions, but then you might be surprised! Funnily enough I drafted this post weeks ago, and then last week a colleague of mine talked about how this was a really difficult question, so I had to post it now ;-)
Another question that he mentioned that students found really difficult is similar to this one:
If an anchor is dropped from a boat into a pond, what will happen to the water level?
A: It will rise
B: It will sink
D: I don’t know
Today I’m going to share a long movie with you, but I’m planning to talk about ship lifts in more detail soon. But just how awesome is it that they can lift ships (SHIPS!) 40 meters up just like that? Each of the troughs carries 5,800 t water. You see the counterweights move when the troughs move, and it is totally fascinating.
I went there with my parents, but this is pretty much all they saw of me for a very long time :-) Weirdly enough I was the only person standing right at the railing. Well, maybe not so weird considering how wet I got. But you’ve gotta do what you’ve gotta do and I definitely enjoyed watching!
The movie below is sped up by a factor 3.5 because there was so much footage that I wanted to show…
And then I had those two new tiny cans sitting in my kitchen. My parents came over and we talked about how I am so happy I got those tiny cans, because it is less equipment to lug around when I travel to workshops or courses. And then my mom says that she has never seen the experiment for real. So of course, I have to show her. And what happens? This!
Yes, the regular coke might have sunk a little deeper, but this is really not as impressive as the experiment is supposed to be!
Good thing I moved the cans (which a friend’s friend brought to Norway for me, which I then brought from Norway to Iceland and then back to Norway) with me to Germany… As you see: The large cans still show what I wanted them to show!
So who knows what is going on here? Too much head space in the tiny cans relative to the amount of soft drink they contain? New formula? Anything else?
And the moral of the story: ALWAYS try your experiments when you are using new equipment before you show them to anyone. Who would have thought that this experiment was not fail safe???
Extremely simple experiment to illustrate the effect of density differences.
At room temperature, will coke cans float or sink in freshwater? And how about coke light?
Btw, this experiment is only easy if you are in a country where you can get the right soda brand both in normal and in light version in cans. Thanks to Anna’s friends for importing them for me! As we found out – Red Bull does not work.