1) Newton's first law states that an object remains at rest or in uniform motion unless acted upon by an external force. 2) Newton's second law defines force as equal to the mass of an object multiplied by its acceleration. 3) Newton's third law states that for every action there is an equal and opposite reaction between two objects interacting with one another.

1. Force and Laws of Motion

4. Laws of Motion
Aristotle
A constant external force must be
applied continuously to an object in order to
keep it moving with uniform velocity.

5. Galileo
No force is required to keep an object
moving with constant velocity
It is the presence of frictional force
between the object and the surface on which it is
moving, the larger the distance it will travel before
the object coming to rest.
After Galileo, newton made a systematic
study of motion and extended the ideas of Galileo.

8. Newton’s Law
Newton’s First Law
* Define the Force
Newton’s Second Law
* It gives the quantitative and dimensional
definition of force
Newton’s Third law
* Explains the nature of force

9. Newton’s First Law of Motion
An object remains in a state of rest or a uniform
motion in a straight line unless compelled to change
that state by an external force.
In other words, all objects resist a change in
their state of motion.
This law is based on Galileo’s law of inertia.
Newton’s first law of motion deals with the
basic property of matter called inertia and the
definition of force.

10. Inertia
Definition:
An object cannot change its state by itself.
Three types of Inertia:
* Inertia of Rest
* Inertia of Motion
* Inertia of Direction

11. Inertia of Rest
It is the inability of the body to change its
state of rest by itself.
Ex: A book lying on the table will remain at
rest, until it is moved by some external agencies.

12. Inertia of Motion
It is the inability of the body to change its
state of motion by itself.
Ex: A passenger sitting in a moving car
falls forward, when the car stops suddenly.

13. Inertia of direction
It is the inability of the body to change its
direction of motion by itself.
Ex: when a bus moving along a straight line
takes a turn to the right, the passengers are thrown
left.
The inertia of a body is directly proportional
to the mass of the body.

14. FORCE
Newton was the first one to give an
exact definition for force.
Force is the external agency applied
on a body to change its rest and
motion.

15. Rest
When a body does not change
its position with respect to time.
Motion
The change of position of an
object with respect to time.

16. How to measure???
It is measured in SI unit
of newton and represented by the
symbol
F

17. Formula
Force = mass x acceleration
F= ma

18. Mass
The quantity of matter contained in a body. The
SI unit of mass is kilogram (kg)
Acceleration
A particle defined as the rate of change of
velocity. It is vector quantity;
a= dv / dt
Its SI unit is m/s^2

19. Force used Physical quantities
• Work = force * distance
• Pressure = force / area
• Impulse = force * time
• Surface tension = force / length
• Magnetic Induction = force/(current*length)

27. Newton’s Second Law
The rate of change of momentum of a body is
directly proportional to the external force applied
on it.
F = dp / dt

28. By the definition of momentum
where m is the mass and v is the velocity
By substituting the definition of acceleration;
F = ma

29. Newton’s First Law of motion deals with
the behavior of objects on which all existing
forces are balanced.
Newton’s Second Law of motion deals with
the behavior of objects on which all existing
forces are not balanced.

30. The force acting on a body is measured by the
product of mass of the body and acceleration
produced by the force acting on the body.
The second law of motion gives us a measure
of the force
One Newton
when acting on unit mass produces unit
acceleration.
Unit = newton or kg m/s2
Dimensional Formula = MLT -2

31. Impulsive Force
A very great force acting for a very short
time on a body so that change in the position of
the body during the time the force acts on it may
be neglected.
Ex: The blow of a Hammer
Impulse (J) = Force X time
J = F X t
Impulse of a force is a vector quantity and its unit
is N s

32. Momentum
The quantity of motion of a moving body
measured as the product of mass and velocity.
Simply defined as the mass in motion.
p = mv
unit: kg m/s ; Momentum is a vector quantity;
Dimension : ? ? ???

33. Principle of Impulse and momentum:
J = F X t
= ma X t ( a= v-u/t )
= m X (v-u)/t X t
= mv-mu
= Final momentum- Initial momentum
of the body of the body
= Change in momentum
Avg . Force = (mv–mu) /t

34. Newton’s Third Law
For every action, there is an equal and
opposite reaction
.
F12 = - F 21

36. The third law states that all forces
between two objects exist in equal magnitude
and opposite direction:
If one object A exerts a force FA on a
second object B, then B simultaneously exerts a
force FB on A, and the two forces are equal and
opposite: FA = −FB
The third law means that all forces
are interactions between different bodies.

38. Law of conservation of Momentum
J = mv - mu
( J=0 )
0 = mv – mu
mv = mu
Final Momentum=Initial Momentum

39. The total Momentum of the system is always
constant.
i.e When the impulse due to external forces is
zero, the momentum of the system remains
constant.
In the case of a head on collision between
two bodies.

42. The force acting on one body is equal in
magnitude and opposite in direction to the force
acting on the other body.
Both forces act for the same interval of time.
F1 be force exerted by A on B (Action)
F2 be force exerted by B on A ( Reaction )

43. F1 acting on the body B for a time t, Velocity u2 to
v2.
F1= mass of the body X acc. Of the body B
= m2 X (v2-u2)/t
F2 acting on the body A for a time t, Velocity u1 to
v1.
F2= mass of the body X acc. Of the body A
= m1 X (v1-u1)/ t

44. F1 = - F2
m2 X (v2-u2)/t = - m1 X (v1-u1)/t
m2( v2-u2) = - m1 (v1-u1)
m2v2 - m2u2 = - m1v1+ m1u1
m1u1 + m2u2 = m1v1 + m2u2
Total mom. Before impact = Total mom. after impact
Total momentum of the system is Constant.