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EXERCISE 13 : Force and Motion

Heat & Temperature
Introduction
- Force and motion are fundamental concepts in physics that describe the interaction between objects.
- Force is any influence that causes an object to undergo a change in speed, direction, or shape.
- Motion refers to the change in position of an object over time.
Newton’s Laws of Motion
1 First Law (Law of Inertia)
- An object at rest remains at rest, and an object in motion remains in motion with the same velocity unless acted
upon by an external force.
- This law describes the concept of inertia, the tendency of objects to resist changes in their state of motion.
2 Second Law (Law of Acceleration)
- The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to
its mass.
- Mathematically, \(F = ma\), where \(F\) is the net force applied, \(m\) is the mass of the object, and \(a\) is the
acceleration produced.
3 Third Law (Action-Reaction Law)
- For every action, there is an equal and opposite reaction.
- When one object exerts a force on another, the second object exerts an equal but opposite force on the first
object.
Applications of Newton’s Laws
According to first law
1 A train at rest on a level track will not move unless pulled by an engine.
ii Book lying on a table remains at rest unless it is lifted or pushed.
iii A man sitting in a bus falls backward when it starts.
According to second law
This law enables us to measure a force and establish the fundamental equation of dynamics. Momentum means
the product of mass and velocity.
i.e., Rate of change of momentum
mv-mu = m(v-u)

t t
= m.a.
where
a = Acceleration
f = force
But rate of change of momentum proportional to external force.
External force = ma
Force = Mass x Acceleration
Hence force may be defined as follows: Force. Force is an external effort which changes or tends to change the
state of rest of a body or of uniform motion in a straight line.
According to third law
i When a sailor wants to get away from the shore, he presses the shore with a stick. So the shore presses the
boat with an equal force in the opposite direction.

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