Verify equilibrium conditions for parallel forces using a meter rod, spring balances, and weights by balancing applied forces and checking torque.
Apparatus
Two spring balances, two iron stands with clamps, a meter rod, a sharp wedge, a weight box, and a thread.
Procedure
First, find the center of gravity (G) of the meter rod by balancing it on a sharp wedge. Then, suspend each spring balance from the clamps of the iron stands and check the zero correction for both balances.
Next, place the stands about 60–70 cm apart. Suspend the meter rod edgewise by two loops of thread attached to the hooks of the spring balances. Ensure that the loops hang vertically, the rod remains horizontal, and the graduations face the observer.
Now, note the readings of both balances and add them to obtain the total weight (W) of the meter rod. After that, suspend a suitable weight (w) at the center of gravity (G) using another loop of thread. Adjust the setup again so that the meter rod stays horizontal.
Record the corrected readings of the two spring balances (P and Q). Measure the positions of loops at A and B on the meter rod and determine the distances AG, BG, and AB.
Finally, take P and Q as parallel forces (acting upward) and verify the condition of equilibrium. Then, consider P and R as unlike parallel forces and again verify the equilibrium condition.
Observation and Calculation
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Center of gravity of the meter rod (G): … cm
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Zero correction for balance P: … g dynes
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Zero correction for balance Q: … g dynes
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Weight of meter rod (W): … g dynes
Precautions
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Always note the zero corrections carefully.
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Keep the balances and supporting loops vertical.
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Hold the meter rod horizontally and edgewise.
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Ensure loops are parallel to the meter-rod graduations.
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Suspend heavier weights at the center of gravity.
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Slightly displace the pointers before taking readings.
Viva Voce
Q1. What are like and unlike parallel forces?
Ans. Like parallel forces act in the same direction, while unlike parallel forces act in opposite directions.
Q2. When is a body said to be in equilibrium?
Ans. A body is in equilibrium when no resultant force acts on it, and it either stays at rest or moves with uniform velocity—meaning both translational and rotational accelerations are zero.