Science Buddies: "Ask an Expert"

I am a parent that is helping out in my child's science class in elementary school. The other day in a high school chemistry class, I saw something that I thought would be a neat class project, but I don't know how it works.

It was a shoebox with string coming out of each end. At the end of each string was tied a wooden dowel. When you pulled on one end of the string, the other end was pulled into the box up to the dowel. You then pulled on the dowel up against the shoebox and the other end of the string was then pulled into the box up to the dowel.

Here is the part I can't figure out. On one end, the string coming out of the shoebox was was about 6" long. The string coming out of the other end of the shoebox was about 30" long. So, when the 6" of string was pulled out of the box, the 30" of string was pulled into the box up to the dowel. When you pull on the dowel on the 30" end, all 30" comes out of the box and the 6" piece on the other end of the box is pulled into the box up to the dowel. You can pull back and forth on each end and so you always have either 6" of string out of the box on one end, or 30" of string out of the box on the other end.

How does this work and where on the INTERNET can I find a list of the materials needed and instructions on how to build it?

Hi ricknatale!

I was unable to directly answer your question. I'm sorry. The web sites I found mostly talked about making musical instruments. I've listed six sites below related to musical instruments plus one miscellaneous site. These may suggest a project for your child.

musical instuments:

http://www.vsosuperkids.com/kids/activi ... string.htm
http://pbskids.org/rogers/R_house/object1.htm
http://troop851.ellenbecker.net/Sounds%20of%20Music.htm -
has 5 instruments plus 12 links
http://www.reachoutmichigan.org/funexpe ... uitar.html
http://pbskids.org/zoom/activities/sci/guitar.html
http://www.highlightskids.com/Express/C ... lcimer.asp

a miscellaneous alternate (a shoebox wagon that maybe too elemtary):

http://www.treehousetv.com/parents/acti ... s_Pg27.pdf

What you're saying is that when the 6" side was pulled, all of the 30" would be pulled into the box? And if the 30" side was pulled, only 6" would be brought in?

I have a theory on this, though I'm not sure what a dowel is. Say there were two rods connected together, one much smaller than the other.
------_________
------|-------------|
===|--------------|
------|________|

Like this. Please ignore the " - " s.

The 6" string is tied around the smaller part, while the 30" is around the large part. Thus, for each rotation, only, say .25 inches of the small string would be wound/released for every 4 inches of the longer. This is only a theory, however.

I hope that helped you.

SigmasonicX wrote:What you're saying is that when the 6" side was pulled, all of the 30" would be pulled into the box? And if the 30" side was pulled, only 6" would be brought in?

I have a theory on this, though I'm not sure what a dowel is. Say there were two rods connected together, one much smaller than the other.
------_________
------|-------------|
===|--------------|
------|________|

Like this. Please ignore the " - " s.

The 6" string is tied around the smaller part, while the 30" is around the large part. Thus, for each rotation, only, say .25 inches of the small string would be wound/released for every 4 inches of the longer. This is only a theory, however.

I hope that helped you.

I think SigmasonicX has the right idea. It's similar to gear reduction or a compound pulley system. Think about the size of the rear sproket on a bicycle tire verses the size of the tire itself. For every revolution of the wheel, the distance traveled by a point on the tire is much greater than the distance traveled by a point on the sprocket. So what could be inside the box would be two wheels connected to the same axis. A string wound on the larger wheel would pull out 30 inches while a string on the smaller wheel would pull out 6.

This is just one idea. There may be others.