IGCSE Physics

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/EnergyPowerTimeTemperature etc	Examples:-DisplacementVelocityAccelerationForceWeightMomentumetc

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1. Distance and Displacement.

 

Distance is scalar (value only)

Displacement is vector (value and direction)

Both measured in m (SI unit)

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2. Speed and Velocity.

 

Speed (Scalar)

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)

 

• Speed is the distance traveled divided by the time taken to travel that distance.

• Speed is important in describing motion because it tells how fast an object is moving away from its beginning position.

• The units for speed are often m/s, but can be any distance unit divided by a time unit.

• Direction of Motion Speed and direction of motion are combined when describing an object’s velocity.

• Velocity is a quantity that tells both how fast an object is moving (its speed) and which way it is going (its direction of motion).

• Acceleration Sometimes the velocity of an object changes. The change in velocity over time is called acceleration.

• Acceleration can be a change in speed, a change in direction, or both.

• The most common units of acceleration are meters per second per second, or (m/s)/s.

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 3. Acceleration. (Vector) “a”

 

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