The Homely Scientist

My daughter A told me last week, while I was at the conference, that she had a homework assignment to do this weekend and wanted us to do it together.  No matter what it was, I was going to say yes.  Single dads don’t get that option often.  Regardless, then she said it was to build a simple machine.  W00t!  Science fun!

When I picked the kids up on Friday morning I found out the details.  She had to design and build a device that used two simple machines and would go at least 2 meters (6.5 feet).  Bonus points were given for coming back and/or carrying something.  Oh and once she let go or gave the device its initially energy, she couldn’t touch it.

No sweat.  I knew what to build in seconds.  The Can Car.  This is a super easy project and would be great for rainy day races.  Before I get into the Can Car, and the fun I had with the project (because it didn’t work the first time), let’s talk simple machines.

From Wikipedia a simple machine is:

In physics, a simple machine is any device that only requires the application of a single force to work. Work is done when a force is applied and results in movement over a set distance. The work done is the product of the force and the distance. The amount of work required to achieve a set objective is constant, however the force required to do this can be reduced provided the lesser force is applied over a longer distance. Increase the distance and reduce the force. The ratio between the two is the mechanical advantage.

What are the simple machines?  Here’s the list:

• The inclined plane
• The wheel and axle
• The lever
• The pulley
• The wedge
• The screw

 When I took physics I think the screw was considered an inclined plane, no matter A was using the same list …

For the can car you see that the wheel and axle are there, but what is the second one?  That was something I was pondering too, and wanted to make sure I was on solid footing if challenged by a teacher (sorry a grade 4 teacher isn’t a science authority in my book, but I wanted to have a good argument in case A got dinged on the project).  If you look at the PBS site there is a pencil used to wind up the rubber band to provide power.  I’m calling it a lever.  To me it is the same as the crank on a bike or winch.  The lever lets you transfer energy.  Works for me.

Okay making it was fun.  Had some challenges like a poor supply of rubber bands (I wound up using an elastic from an old conference nametag holder–good thing I’m a packrat!) and a few other improvisations.  And the biggest challenge was the first couple versions didn’t work.

See our initial design was based on a spool racer.  Which uses all the same principles of physics, but the major difference is that a spool is the wheel, not a can.  Oh and at the lever end, it’s a washer not a bead.  These two things combined made for a very frustrating first try.

See I used an improvised washer and a very strong rubber band (broccoli bands rock).  The tension was too much.  The chop stick couldn’t turn.  Bad news.

A and I did what any good scientist would do, we went back and did more research.  Okay she researched and I experimented.  I had a vague memory of a different version of the can car that would come back to you, so I tried that one from memory (couldn’t find it online).  After a lot of tinkering we got it to work.  The success factors were two-fold.  First was using a metal nut between the lid and the chop stick.  Second was using liquid soap to grease the lid on the chop stick end.

And I tell you, that thing when wound up tight, flies across the floor.  And bonus, because it’s a can with covered ends, it can carry stuff!

Bonus points!

For A, this was a good experience in research, trial and error, and experimentation.  For me it was just fun to play with science and share that with my kids.

 

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This entry was posted on Monday, April 23rd, 2007 at 1:19 pm and is filed under Science Education, Science at home, Science experiments to try, Science for Kids. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.