Monday, March 23, 2015

Simple Machines: Screws

There are lots of fun things to learn about screws! We tried screwing several types of screws (pointed tip, blunt tip; threads close together, threads far apart; etc.) into wood so we could see how those differences affected the force needed to drive them in. We also compared the difficulty of pulling out screws from a styrofoam plate versus pulling out nails from that same plate. We saw that screws definitely hold things together more tightly than nails do!

We saw how this worked in another context using two milk jugs filled with water. One jug had a screwed-on lid and one had a snap-on lid.
The boys threw the jugs down onto the sidewalk as hard as they could…
and the snap-on lid popped off immediately upon impact! The screw-on lid stayed put.
Then we tried stomping on the same jugs. I think we eventually got both lids to come off, but it took a lot more force to get the screw lid dislodged!
Sebby got the milk carton stuck on his foot. We all thought that was really funny.

Next, we made two models. They were both different versions of screws: an Archimedes Screw and an auger. (I think the only difference between those two things is that an auger is usually used for solid material like dirt, and an Archimedes Screw is used for water and irrigation.) We kind of just made up the Archimedes Screw based on pictures, but some instructions can be found here.
The Archimedes Screw worked really well. You can see some of the water, after having been "screwed" up from the bottom bowl, dripping out into the top bowl. Very useful!

The instructions for making the auger came from a post here.
They were good instructions, but we didn't feel that our auger was a great success. The "threads" of the screw didn't fit tightly enough inside the bottle, but when we made them fit more tightly, they didn't turn freely enough. And there was too much give on the threads, so that the cereal could easily fall between them.
Still, we managed to get a few rice crispies up the screw into the upper bowl, so we got the general idea of how it worked. And we were lucky enough to encounter an actual auger doing work on the highway nearby a few days later, so that was exciting! :)

We made these "edible screws" for our snack using string cheese and refrigerated crescent roll dough. I liked the way they show so clearly how an inclined plane wrapped around a central core makes a screw!
Bake them at 375 for 10 minutes or so.

We got a lot of great ideas from this post. (The lady that writes these plans is awesome. We've used her Revolutionary War lesson plans and others, and they are always SO full of fun things to try.)

We liked this video about the screw and the wheel.

I thought about having the children make the toy helicopters shown here to demonstrate how a screwing motion can, by increasing the distance traveled, decrease the force with which something falls—but we didn't end up having time for that.

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