 Section 1: Forces and Motion

You will learn following topics in this section

a) Units

b) Movement and position

c) Forces, movement, shape and momentum

d) Astronomy

a) Units

On this and next two pages you will learn Physical quantities, their definitions and units.

Students must learn units by heart

S.NoQuantity with DefinitionSymbol used for quantityunitSymbol used for unit
1

MASS

Definition: Amount of matter present in a body.

m Kilogram kg
2

DISTANCE

Distance's definition is not a part of syllabus.You can safely ignore it.

For curious people only

Definition: Distance is the total lenght covered by a moving object without consideration of the direction of motion, that is, only the magnitude is important.

Note: "magnitude" means value or number. For example; 5 meters-- 5 is the magnitude;4 seconds-- 4 is the magnitude etc.

s Meter m
3

SPEED

Definition: Rate of change of distance per unit time.

But

Note 1: if in exam definition of speed is required just write down the following formula. Caution: Never write formula in symbolic form only in word form like the one given above.

Note#2: Syllabus talks about Average Speed only. So whenever the word speed is used it is always referred to the Average Speed.

Note#3: time is usually taken in second; unless told otherwise.

v Meter/second m/s
4

VELOCITY

Definition: Rate of change of distance per unit time in a particular direction.

OR

Rate of change of displacement.

For exams write word equation for definition as given below Note#1: There is fundamentally no difference between speed and velocity except that velocity has direction.

Velocity = speed + direction.

Note#2: It is a vector quantity.

How speed is different from velocity?

only in direction!

A car driving along a highway from one town to another, its speed might be constant, but the velocity changes as it will change several directions during the course; as shown in the following figure The speed is same on all three points while direction is being changed therefore velocity changes.
If you’re moving along at 25 m/s and then you come to a bend in the road,your velocity changes because your direction changes.

v Meter/second m/s