|MadSci Network: Engineering|
The relative temperature of the water will certainly have an effect on the rubber band, but the effect will vary in intensity based on a number of other factors. Among them: thickness of the band, the time in the water, and the weight of the object putting stress on the band.
In general, the elasticity of the rubber band will decrease with the decrease in temperature of the water it's soaked in. However, by placing a weighted object on the band, you are looking at two different variables. If you measure how far the rubber band stretches with a fixed weight object, you are testing elasticity. If you are testing for how much weight the band can bear before breaking, you are actually testing it's tensile strength. It's important to define this part of your experiment before proceeding. Since you asked about elasticity, I'll assume that's what you are testing.
Like most matter, the rubber contracts when it gets colder. The
molecules in the rubber bad get closer together. This affects the
elasticity in two ways.
1) The rubber band will not stretch as far. When the weight is placed upon it, you'll see less of a bow under the weight.
2) The rubber band will be able to sustain less weight (Back to the tensile strength thing). Since the forces holding the molecules of rubber together are stronger, they are less able to give and stretch, and the rubber band is more likely to snap.
As I mentioned before, there are more variables to consider, and you should probably look into the nature of your rubber band before conducting your experiment. Some kinds of rubber aren't as elastic as others, case in point - belts in a car or tires, as opposed to surgical gloves. Other variables include air pressure, room temperature, water temperature (hot water makes rubber more elastic, but the heat may rob the rubber of some elastic properties*), etc.
You are on the right track to conducting a valid experiment. To answer your specific question, a bowl of water will probably work well. Also remember:
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