A mass is suspended by two identical springs, which are connected in series as shown in the photograph at the left below from a fixed point. Each spring has a parallel string loosely connected from the upper and lower ends to the center as shown in the photograph at the right.
The coupling clip between the two springs can be disconnected such that the mass will then be supported from the fixed point by two parallel spring-string units, one with the spring on top and the string on the bottom, the other with the string on the top and the spring on the bottom.
When the series spring support is disassembled so that the mass is supported by two series spring-string combinations, where will the mass be relative to its initial position as shown in the figure above?
- (a) The mass will be at a higher position.
- (b) The mass will be at a lower position.
- (c) The mass will be at the same vertical position.
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The answer is (a): the mass will be at a higher vertical position with the spring configuration of two parallel series spring-string combinations, as seen by comparing the two photographs below.
When the two springs are in series the entire weight is pulling on both springs. With the series/parallel setup each spring only supports half of the weight, and is therefore extended only half as much. The small amount of slack in the string cannot make up for the reduced spring extension, and the mass moves up.