CLASS 9 MOTION PART 2

Average Velocity:

    •  If a particular under goes a displacement s₁ along a straight line t₁ and a displacement s₂ in time t₂ in the same direction, then Average velocity = s1+s2t1+t2   .

    •  If a particle undergoes a displacement s₁ along a straight line with velocity v₁ and a displacement s_s with velocity  v₂ in the same direction, then

                                      Average velocity = (s1+s2)v1v2s1v2+s2v1   .

    •  If a particle travels first of the displacement along a straigh line with velocity v₁ and the next half of the displacement with velocity v₂ in the same direction , then

                                Average velocity = 2v1v2v2+v1  (in the case(b) put s₁ = s₂)

    •  If a particle travels for a time t1 with velocity v1 and for a time and for a time t2 with velocity v2 in the same direction, then

                                   Average velocity = v1t1+v2t2t1+t2    .

    •  If a particle travels first half of the time with velocity v₁ and the next half of the time with velocity v₂ in the same direction, then

                    Average velocity = v1+v22   (in the case d put t₁ = t₂) .

    •  Velocity of a particle is uniform if both it magnitude and direction remains unchanged.

    •  Velocity of a body changes when magnitude or direction or both change.

Acceleration

The rate of change in velocity is called acceleration and is measured in metre per square second in the international system of units.

             Acceleration, a = Final velocity - Initial velocityTime

Time 

Note: The negative acceleration is termed as retardation.

Differences Between Distance and Displacement

S.No.	DISTANCE	DISPLACEMENT
1.	It is defined as the actual path traversed a body	It is the shortest distance betweeen two points by between which the body moves.
2.	It is a scalar quantity.	It is a vector quantity.
3.	It can never be a negative or zero.	It can be negative, zero or positive.
4.	Distance can be equal to or greater than displacement.	Distance can be egaual 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 types of path followed by the body.	Displacement between two points does not give full information of the types of path followed by the body.
7.	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.
8.	Distance in SI is measured in metre.	Displacement in SI is measured in metre.

Differences Between Speed and Velocity

S.No.	SPEED	VELOCITY
1.	It is defined as the rate of change of distance.	It is defined as the rate of change of displacement.
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 posituve.
4.	Speed is velocity without direction.	Velocity is directed speed.
5.	Speed may or may not be equal to velocity.	A body may possess different velocities but the same speed.
6.	Speed never decreases with time. For a moving body, it is never zero.	Velocity can decrease with time. For a moving body , it can be zero.
7.	Speed in SI is measured in ms-1	Velocity in SI, is measured in ms-1