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course
2:15 pm July 6
Experiment 7. Measuring MassesUsing a balance constructed from pieces of shelf standard, balanced on a knife edge and with a brass damping cylinder partially submerged in water, we investigate the rotational displacement of the balance from equilibrium in response to the addition of small weights. We then use the balance with the mass set to precisely measure the masses of various objects. See video clip on CD EPS01.
You have been supplied with a mass set and a crude but effective and precise balance. With this balance you can with reasonable accuracy determine the mass of an object by placing it on one side of the balance and adding masses from the mass set to achieve a balance. The balance is very sensitive to small changes in mass, capable of detecting changes on the order of .01 grams.
The mass set consists of masses of .1 gram, .2 gram, .3 grams, .5 gram, 1 gram, 2 grams, 3 grams, 5 grams, 10 grams, 20 grams, 30 grams, 50 grams and 100 grams. Using various combinations of these masses you can obtain any mass from .1 gram to over 200 grams, in increments of .1 gram. Each mass is accurate to within +-.5%.
Answer the following questions:
• Why is it essential that the balancing pans be placed at equal distances from the balancing point?
To make everything equal and to not mess up the results
• How much would the result of weighing a 40 gram object be affected if one pan was positioned 29 cm from the balancing point, and the other 28 cm from this point?
It would be off by a few grams because of the unequal placements and positions of 29 cm and 28 cm
• If when determining the mass of a small washer, the beam position could be brought to within .1 cm of its original position by a balancing mass of 1.21 grams, then what might be the mass of the washer?
1.23 grams
• Why does the beam not balance at its equilibrium position when unequal masses are added at the two ends?
Because they are unequal masses, will not balance at equilibrium
• Why does the beam not balance at its equilibrium position when equal masses are added at unequal distances from the balancing point?
Because of the difference and unequal distances, this skews with the results and does not balance the beam to get it in equilibrium
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