Weights

[brezinkl]

For my science fair project, I am testing the tensile strength of different types of beams. The beams are made of plastic and the weights will be suspended from them in a fabric bag. I am wondering what I should use for weights. Your suggestions are greatly appriciated.

[rmarz]

When deciding what to use for weights, the first question that comes to mind is "what is the approximate range of weight that might be required to make the beam fail". This depends on the scale, material and design of your beam. It might be as little as a few ounces or pounds or as much as tons (although you are probably working with something that is at the low end of this spectrum). If you are looking for something in the range of a few pounds; scrap steel, large bolts, iron pipe, scrap re-bar, free-weights (barbell weights for example) are candidates for high density weight. Be mindful that you will probably be testing to destruction while noting deflections, so take care to protect yourself and your environment (floors, tabletops, fingers etc.) from falling masses when the bean fails. Try to make the distance it falls as short as practical. Another method might be to use a calibrated spring scale similar to one used by fishermen to weigh their catch. Perhaps you can borrow something like that from a friend or school lab. If you use something like a suspended spring scale, be sure to adjust your figures for the weight of the scale in your calculations if it's own weight can't be adjusted out. If you use loose weights you will need some form of scale (postal scale for small masses, bathroom scales for heavier objects) to measure your weights for the experiment. Hope this helps.

[acgoldis]

Hi!

The barbell weights are an interesting idea. They're flat and have known weights. However, how are you going to get the weights from the gym into the lab for your experiments? Do you have a set of weights in your house?

You could conceivably take a bathroom scale (or kitchen scale) and fill a bunch of shoeboxes or something like that until they have known weights. Then you can do the experiment at home where you don't need to worry about breaking stuff. You can also adjust weights if you want to more easily.

ACG

[Craig_Bridge]

You might want to think about using a plastic bucket instead. You can then slowly add sand or water to bucket until the beam breaks or deflects to your test criterion and then weigh the bucket to determine how much force was required. This method is often used in popsickle stick or toothpick bridge strength contests.