EXPERIMENT: 1 (THIRD
LAW OF MOTION USING SPRING BALANCE)
# Our Aim
To study the Third Law of Motion using two spring balances.
# The Theory
Newton’s Third Law of Motion states: ‘To every action there is an
equal and opposite reaction’.
It must be remembered that action and reaction always act on
different objects. The Third Law of Motion indicates that when one object
exerts a force on another object, the second object instantaneously exerts a
force back on the first object. These two forces are always equal in magnitude,
but opposite in direction.
These forces act on different objects and so they do not cancel
each other. Thus, Newton’s Third Law of Motion describes the relationship
between the forces of interaction between two objects.
Whenever two bodies interact with each other, the force exerted by
the first body on the second is called action. The force exerted by the second
body on the first body is called reaction. The action and reaction are equal
and opposite.
For example, when we placed a wooden block on the ground, this
block exerts a force equal to its weight, W = mg acting downwards to the
ground. This is the action force. The ground exerts an equal and opposite
force W’ = mg on the block in the upward direction. This is the reaction force.
Applications of Newton’s Third Law of Motion
1. A gun recoils when a
bullet is fired from it:
2. A man walking on the ground
3. Rowing a boat
4. A person is moving forward during swimming
5. Rocket propulsion
# Material required:
Iron stand, two spring balance of different least counts.
# Procedure for doing
real Lab:
- Take
two similar spring balances of different ranges, say A and B.
- Note
the least count of the spring balances.
- Attach
the ring of spring balance A on a hook fixed in the wall and the spring
balance B is attached to the hook of spring balance A.
- Hold
the spring balances exactly horizontal to the table.
- Pull
the ring of spring balance B gently.
- Observe
and note the reading of both the spring balances.Repeat the experiment by
applying different forces.
# Procedure for doing
simulator:
- Change
the ‘Applied force’ slider and observe the reading on the two spring
balances.
- Repeat
the experiment by applying different forces.
- Click
on the reset button for reset the experiment.
# Observations:
- Least
count of the spring balance = value of 1 small division
- Least
count of the spring balance A=………N
- Least
count of the spring balance B =…………………N
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No. of observations
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Reading of B (Second spring balance) when force applied
(N)
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Reading of A (First spring balance) when force applied (N)
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Difference in reading of A and B (N)
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# Result:
The readings on both the balances are the same in each case. Thus
action and reaction forces are equal and opposite and act on two different
bodies.
# Precautions:
- Spring
balance of different least count should be taken.
- The
spring balance should be brought in elastic mode before doing the
experiment.
- The
second spring balance should not be pulled beyond its elastic limit.
- The
reading of the spring balance should be taken without any parallax error.
# Learning Outcomes
The student will understand:
- Action
force
- Reaction
force
- Newton’s
Third Law of Motion
