Question

self reflection notes on motion​

Answer 1

Notes on Motion

MOTION ( NOTES )

Differece between scalar & vector quantities :

Scalar quantities
Vector quantities
1
These are completely specified by their magnitude only.
These are completely specified by their magnitude as well as direction
2
These change by change of their magnitude only
These change by change of either their
magnitude or direction or both
3
These are added or subtracted by laws of
ordinary algebra like 4m+5m=9m.
These are added or subtracted by laws of
vector addition.

DISTANCE AND DISPLACEMENT
Distance : The length of the actual path between the initial and the final position of a moving object in the given time interval is known as the distance travelled by the object.

Distance = Length of path I (ACB)
Distance is a scalar quantity.
Unit In SI system : metre (m)
In CGS system : centimetre (cm)
Large unit Kilometre (km)

Displacement:– The shortest distance between the initial position and the final position of a moving object in the given interval of time from initial to the final position of the object is known as the displacement of the object.
Displacement of an object may also be defined as the change in position of the object in a particular direction. That is,
Displacement of an object = Final position – Initial position of the object.
Displacement of an object may be zero but the distance travelled by the object in never zero.
Distance travelled by an object is either equal or greater than the magnitude of displacement of the object.
Displacement = Length of path II (AB) A to B,
displacement is vector quantities.
Units In SI system : metre (m)
In CGS system : centimetre (cm)
Ex. A train goes from station A to station B as shown in figure. Calculate
(i) the distance travelled by the train and
(ii) the magnitude of the displacement of the train on reaching station B.

Sol. (i) Distance travelled by the train = 50 +100+ 200+ 400 = 750 km.
(ii) Magnitude of the displacement in going from station A to station B = 400 km.
DIFFERENCES BETWEEN DISTANCE AND DISPLACEMENT

Distance

Displacement

1

It is defined as the actual path traversed by a body.

It is the shortest distance between two points which the body moves.

2

It is a scalar quantity

It is a vector quantity'

3

It can never be negative or zero

It can be negative, zero or positive.







4

Distance can be equal to or greater than displacement

Displacement can be equal to or less than distance.

5

Distance travelled is not a unique path between two points.

Displacement is a unique path between two points.

6

The distance between two points gives full information of the type of path followed by the body.

Displacement between two points does not give full information of the type of path followed by the body.

'

Distance never decreases with time, for a moving body it is never zero.

Displacement can decrease with time for a moving body it can be zero.

S

Distance in SI is measured in metre

Displacement in SI is measured in metre.


• Uniform motion: When an object covers equal distances in equal intervals of time, it is said to be in uniform motion.
• Non-uniform motion: Motions where objects cover unequal distances in equal intervals of time.
• Speed: The distance travelled by an object in unit time is referred to as speed. Its unit is m/s.
• Average speed: For non-uniform motion, the average speed of an object is obtained by dividing the total distance travelled by an object by the total time taken.

• Velocity: Velocity is the speed of an object moving in definite direction. S.I. unit is m/s.

• Acceleration: Change in the velocity of an object per unit time.

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