Motion in a straight line

Parameters of motion

There are four parameters used to describe motion in a straight line viz:

*i. Distance (s) or displacement (s)*

*ii. Speed or velocity (v)*

*iii. Acceleration (a) and *

*iv. Time (t)*

Kinematics is the study of bodies in motion without the forces that act on them. Dynamics is the study of objects in motion with the forces acting on them.

**Distance**:- It is the space between two points e.g. 100m

**Displacement**:- This is the distance travelled in a given direction e.g. 200E of the market.

**Speed**:- This is the rate of change of distance with time.

V= s or speed= s unit in m/s.

**Acceleration**:- It is the rate of change of velocity with time, unit is m/s².

a= v

**Uniform acceleration**:- If the rate of change of velocity with time is constant, the acceleration is said to be uniform

a=v = constant

**Retardation**: This is negative acceleration.

Distance and Displacement

Distance can be said to be the space between two points. Distance could just be 50cm which is scalar, since it has size. But when we have 500m due west, we are now dealing with vector, because it has both size and direction. The 500cm due west is now the displacement.

Displacement could then be defined as the distance moved in a specified direction.

Speed and Velocity

The term, speed is defined as the rate of change of distance move with time. For instance, if a car covers a distance of 80km in 1 hour, then we can say that the speed of the car is 80km per hour. Hence speed is scalar with its unit of measurement in m/s.

But the term, velocity is vector, because others have both size and direction. Velocity is defined as the rate of change of distance moved with time in a specified direction. If a car is travelling at 50km/h along the eastern part of a road, then we can correctly say that it has velocity of 50km/h due est of the road.

Acceleration and Retardation

Acceleration:- This is the increase in the velocity of a body. The unit is m/s².

Retardation:- This is the negative acceleration i.e. when a car is coming to a stop when brakes are applied.

Uniform speed:- If the ratio s/t is constant throughout the journey, the speed (v) is said to be uniform.

av= speed = total distance travelled

Total time

Velocity is speed measured in a given direction.

Acceleration is the rate of change of velocity with time. Its unit is m/s² i.e. acc= v

Uniform acceleration:- If the rate of change of velocity with time is constant, the acceleration is said to be uniform.

a= v = constant

Rectilinear acceleration in a uniform velocity motion:-

In a motion where uniform velocity is constant there is no change in velocity, the acceleration in such a motion is zero. A non-uniform velocity motion suggests a velocity that changes as the motion progresses.