Lab Manual: Relationship Between Weight of a Body and Force Required to Just Move it | Lab Manuals for Class 9 PDF Download

Objective

Materials Required

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• Learn about the force in taut strings called as Tension.
• Learn about the presence of friction in an object even at rest – Static Friction.
• Learn about the way the tension changes as more and more weight is added to the pan.
• Learn about how the static friction varies as more and more weight is added to the pan.
• Learn to handle a set-up with vertical and horizontal movement.

Theory

• The force of friction always acts in a direction opposite to the direction of applied force. As the force applied on the wooden block to be moved increases, the force of friction also increases accordingly to balance it. This indicates the presence of static friction—friction when an object is at rest.
  
• But the force of friction can increase upto a certain limit. Once the applied force exceeds this limit, the object moves. The maximum value of force of friction, acting between the two solid surfaces just before the object sets into motion is called limiting force of friction or limiting friction. The force is directly proportional to the weight of the object.

Procedure

• Find the range and the least count of the spring balance.
• Measure the weight of the wooden block using a spring balance.
• Arrange the set-up with a wooden block in the horizontal surface and connect it with a spring balance as shown
• Observe the pointer in the spring balance.
• Now apply a small force on the wooden block by pulling the spring balance. Gradually increase the force till the block begins to slide.
• Note the reading on the spring balance.
• Repeat the experiment with increasing weight of 50 g on wooden block and record your observations.

• Range of the spring balance = 0 – 500 g = 0 – 5 N
• Least count of the spring balance = 10 g
• Mass of the wooden block with hook, R = 50 g
• Value of ‘g’ = 9.8 m/s²
  

1. Plot a graph between weight of wooden block, W on V axis and the reading on spring balance, F on ‘y’ axis.
2. The graph obtained is a straight line as shown in the figure.
   

• The force required was found to increase with the increase in the weight of the block.
• The ratio F/W is constant.
• The constant ratio of F/W and the straight line graph indicates the maximum force required to just move the block is directly proportional to the weight of the block.

Precautions

• Reading in spring balance should be noted as soon as the wooden block starts moving.
• The horizontal surface must be clean and dry.
• The spring balance should not touch the wall or any surface.
• The force applied on the wooden block by pulling the string should be gently and gradually increased.
• The string should be inextensible.
• The string should be kept horizontal while the force is applied on the block.