Science Buddies: "Ask an Expert"

I am doing a project where I am testing the strength of plastic beams. I know how much the beams weigh and how much weight they can hold before breaking, what would be the formula for the strength-to-weight ratio? Thanks!

To get the strength-to-weight ratio, simple divide the strength by the weight of each sample. That will give you the "ratio". Make sure you measure the strength and weight using the same units, like "pounds" or "ounces".

A strength to weight ratio is only viable as a means of comparing beam performance if the test conditions are identical.

If the length of the span or end conditions are different, you will get different results for the same cross section beam.
If you are comparing how much weight / force a beam will hold in the middle of the same length span with the same end conditions and load bearing point conditions, then you have a viable comparison; however, you have to specify those conditions somewhere in your data so that somebody else could repeat your testing.