Displacement, Speed, Velocity and Acceleration

Displacement                                                Read other topics in High School Physics

Displacement is a measure of length in a specified direction. Simply put , Displacement can be defined as the distance travelled in a specified direction.

Distance is a measure of length in any direction

Example

Classify each of the followings as a distance or displacement.

i  10m NE

II  23 Km

iii 50cm eastward

iv  28 m towards north

Solution

I, iii and iv are displacement because direction of movement are specified . Only ii is a distance because no direction is specified.

Displacement is a Vector quantity while Distance is a Scalar quantity.

Example 

A car move 100m towards north and 50m towards east . what is the distance and displacement of the car.? if this car move this 50m towards west instead of the east, what will be the effect on the displacement and the distance cover.?

solution 

The distance cover by the car is 100m + 50m = 150m

The displacement of the car is the air distance between the starting position and ending position. this is the hypotenus of the right angle triangle involve

c =√12500 = 111.8m

The direction is

the displacement is 

2. if this car moved 50m  towards west instead of toward east what will the effect be ?

the distance cover remain the same = 150m

the displacement will be

Speed

Speed can be defined as the rate of change of distance with time.

 Speed v  = Change in distance/change in Time = s/t

when v = s/t = constant throughout the movement then it is called Uniform speed.

When v is not constant then it is non-uniform speed or average speed.

Average Speed v = total distance cover/total time taken.

Example

A car initial move at a speed of 10m/s for 30s and change speed to 15m/s for another 40s.

What is the Average speed of the car ?

Solution

Average speed = total distance/total time

For the first 30s , v=s/t, therefore s=vt = 10x30= 300m

For the last 40s , v=s/t, therefore s=vt = 15x40 = 600m

Total distance = 300 + 600 = 900m

Total time = 30 + 40 = 70s

Average speed = total distance/total time = 900/70 = 12.86m/s

Velocity

Velocity is the rate of change of distance with time in a specified direction.

Or Velocity is the rate of change of displacement with time.

Velocity = Speed in specified direction

Therefore velocity is a vector quantity while speed is a scalar quantity.

Example

A car move at a speed of 10m/s in the direction north East

What is the speed and velocity of the car ?

Solution

The speed of the car = 10m/s

The Velocity of the car = 10m/s NE

Acceleration

Acceleration is defined as the rate of change of velocity with time

Or Acceleration is the rate of change of speed with time in a specified direction.

Therefore acceleration is a vector quantity.

Acceleration a =rate of change of velocity/time = v/t

When v/t=constant then the acceleration is uniform acceleration.

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