MOTION

“Kinematics”

Kinematics is the branch of classical mechanics that describes the motion of bodies (objects) and systems (groups of objects)

Main concepts of KINEMATICS

• Distance and Displacement.
• Time
• Speed
• Acceleration
• Force

Physical quantities can be divided into two groups; Scalar quantity and Vector quantity

 Physical quantities Scalar Vector It is completely described by stating its magnitude(size).(has magnitude & no direction) It is completely described by stating its magnitude and direction(has magnitude and direction) Examples:-Length/distanceArea/VolumeSpeedMassWork/Energy Power Time Temperature etc Examples:-DisplacementVelocityAccelerationForceWeightMomentum etc

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1. Distance and Displacement.

Distance is scalar (value only)

It is the total length travelled by an object.

Displacement is vector (value and direction)

It is shortest distance from one point to another in a certain direction

Both measured in m (SI unit)

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2. Speed and Velocity.

Speed (Scalar)

It is the distance travelled per unit time.

S.I. unit of speed is m/s

Speed (v) = distance (d) / time (t)

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Average speed

Speed of a car will never be a constant speed all over the trip (it accelerate and deceleate), so we can calculate the average speed

Average speed = total distance travelled / total time taken.

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Speed VS velocity

Speed (scalar)

It is the distance travelled per unit time. (Rate of change in distance)

Velocity (vector)

It is the displacement covered per unit time. (Rate of change in displacement)

Or Speed of a body in a particular direction”.

Velocity (v) = displacement (S) / time (t)

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3. Acceleration. (Vector) “a

Acceleration is the rate of change in velocity.

S.I. unit of acceleration is m/s2

• Most vehicles do not travel at the same velocity all the time.
• If they speed up, they are said to accelerate.
• If they slow down, they decelerate.
• Acceleration describes how quickly (the rate) velocity changes.

Acceleration is a vector quantity.

Increasing the velocity with a uniform way or rate will cause a Steady acceleration which means “UNIFORM acceleration or constant”

Acceleration (a) = change in velocity /time taken

a = (v – u)/ t

Where

a = acceleration in m/s2

u = initial velocity in m/s

v = final velocity in m/s

t = time taken in s

Notes:-

Acceleration

Positive acceleration (a = +ve)
means increasing velocity.

(There is an acting force to increase its velocity)

Deceleration or retardation

Negative acceleration (a = -ve)
means decreasing velocity.

(There is an acting force to decrease its velocity)

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Motion Graphs

distance-time graphs speed-time graphs 