Position, Distance and Displacement

Physics SS1 First Term

Week 2

Position, Distance and Displacement

Performance Objectives

Students should be able to:
1. Determine the measurement of distance 
2. Determine the concept of direction, position and Position coordinate

Contents 
The position of a point in space is determined by its distance and direction from other points. The statement of position is accomplished by means of a frame of reference or point of reference, which we shall call the origin.

Distance
This is the movement coverage of a body with no emphasis on direction; it is a change in the position of an object with no definite direction.

Displacement 
This is defined as the distance travelled in a specified direction. It is a change in the position of an object which requires distance and direction to specify it.
To further distinguish between distance and displacement, a person strolling 500m to the east and then turning around and walking back (west), a distance of 300 m, the total distance travelled is 800 m but the displacement is only 200 m since he is now only 200 m from the starting position.

Speed 
This is the rate at which a body covers a distance.
Speed = distance/ time, this is an average speed (v) over the distance (s), v = s/t, the SI unit (Standard International unit) of distance is meter, while for time is second, therefore, for speed is meter per second (ms-1), we could have units in centimeters per second and kilometer per hour.

Uniform Speed 
When a body covers equal distances in equal time intervals, no matter how small the time interval may be, the speed is said to be a uniform speed or constant speed.

Velocity
Again, the word velocity and speed are often used interchangeably by most people, it will be fair to do justice to this lingering misconception, while studying motion it is necessary to draw a clear distinction between the two, in speed no direction is specified, while in velocity it is imperative to work on the direction, as treated above, displacement works with considered direction, so we define velocity in terms of displacement.
Velocity is the rate of change of displacement, Velocity = displacement/time, v = s/t.

Uniform Velocity
When a body moves with equal displacement in equal time intervals, no matter how small the time intervals may be, the velocity is said to be a uniform velocity or a constant velocity, its SI unit is also in (ms-1), but in a case where a body moves round a circular path at constant speed, it is said to move with non-uniform velocity, because its direction of motion is constantly changing.

Distance-Time Graph
Measuring the distance covered by a moving object at known time intervals (for instance 6 seconds), and we plot the values of distance on the Y-axis and time on the X-axis of a graph on joining the points, we obtain distance-time graph.
Such graphs do a lot in providing useful information about the motion of the object; at that point on the graph where the distance is a straight line from point 0, the speed (or velocity) is uniform since the body covers equal distance in equal times. The gradient or slope of that straight line is 0 – 10 in meters as the unit of distance divides 0 – 6 in seconds as the unit of time.
Instantaneous Velocity is defined as the velocity at any instant of time. The speedometer of a moving vehicle indicates instantaneous velocity.