# Help with soda can project

profkth
Help! My son has spent countless hours on his high-school physics project, where the challenge is to make a soda can move as far as possible on its own. Nothing can be placed between the can and the floor surface, and nothing can extend beyond the ends of the can by more than 7 mm. Beyond that, anything goes. He is able to get it to move, using rubber bands and batteries taped to the rubber bands, inside the can, but it only moves about 5 feet. He will only get a passing grade on the project if he makes it move at least 10 feet. Any ideas?

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Hi

Have u tried the Sling Shot technique? or have u tried filling the can completely with pressurised soda/gas and then opening the cork so that the can moves forward? or u could even use a spring

Sridhar

profkth
Thanks! What is the sling shot technique?

Njorl
I'm assuming that the batteries are inside the can, wound up with rubber bands. When they are released, they spin, and the can starts turning, and rolls some distance.

Is the can slipping when it starts?
If so, put a few fat rubberbands around it so it will get better traction.

Can you get something denser than a battery? A big stack of steel or copper washers might impart more angular momentum.

Njorl

Hi

Ok, the sling shot technique is one where u use a fully stretched rubber band. However I have been calculating a few things. You would get a better range if u used a spring technique. Here are the procedures:

1) Fix one end of the spring to a vertical rod that stands on the ground.

2)Fix the other end of the spring to the Can and compress the spring to the maximum possible extent. i.e The spring should be completely compressed.

3) Now the tie the can to the stick using strings

4) To release the can, just cut the strings.

4 a) If u don't want to use the strings, u culd hold the can using urself and release it when u want.

5) I don't think this apparatus will have more that 7mm extension on each side.

6) Use a spring with a very high spring constant.i.e. A highly compressible spring that can generate lots of force.

You will definitely get an excellent range as the Force generated by the spring = -K*x, where x = the length to which the spring is compressed and k = spring constant. This provides a momentum to the Can and:

kx = mv, where, m = mass of the can and v = velocity of the can.

Therefore, v = (k*x)/m; Which means that more the spring is compressed, the faster the can goes and thus greater the distance it covers. Don't use a very heavy can or a very light can. Use a Coke Tin with some paper in it .

Hope this helps you.

Sridhar