Displacement (vector)

Displacement (vector)

In physics, displacement is the vector that specifies the position of a point or a particle in reference to a previous position, or to the origin of the chosen coordinate system. When the reference point is the origin, this is better referred to as a position.

A displacement vector is a simplified representation of motion. Namely, it indicates both the length and direction of a hypothetical motion along a straight line from the reference point to the actual position. A motion along a curved line cannot be represented by a single displacement vector, and may be described as a sequence of very small displacements. On the other hand, a distance is typically defined as a scalar quantity and can be used to indicate both the length of a displacement (minimum distance) and the length of a curved path (traveled distance), but not the direction of the motion.

When the reference point is a previous position, the displacement vector is the difference between the final and initial position. This difference, divided by the time needed to perform the motion, defines the average velocity of the point or particle.

In dealing with the motion of a rigid body, the term displacement may also include the rotations of the body. In this case, the displacement of a particle of the body is called linear displacement (displacement along a line), while the rotation is called angular displacement.

Distance Traveled

If the displacement of an object is described by a vector function
mathbf{r}(t):R to mathrm{V}^n,
then the distance traveled as a function of t is described by the integral of one with respect to arc length.
mathrm{d}s is the arc length differential
The arc length differential is described by the following equation:
mathbf{v}(t) is velocity
v(t), is speed

Displacement, position, and velocity

A position vector can be viewed as an hypothetical displacement of a point or particle from the origin of a coordinate system to the location of a point at a given time.

On a graph representing the position of a particle with respect to time (position vs. time graph), the slope of the straight line joining two points on the graph is the average velocity of the particle during the corresponding time interval, while the slope of the tangent to the graph at a given point is the instantaneous velocity at the corresponding time (first derivative of the particle position).

Displacement and the equations of motion

To calculate displacement all vectors and scalars must be taken into consideration . The following formulas can be used to calculate displacement , s.

mathbf{s} = {mathbf{u}t+{1over 2}mathbf{a}t^2}

mathbf{v} = mathbf{u}+ mathbf{a}t

mathbf {v^2} = mathbf{u^2}+2mathbf{as}


mathbf{u} Initial velocity
mathbf{v} Final speed
mathbf{a} Acceleration
mathbf{t} Time
mathbf{s} Distance

  • It should also emphasized that vector directions, negative and positive signs, are important when calculating displacement

Height displacement

Height displacement is the distance an object peaks in height vertically if for example a ball was thrown up in the air and back into the owners hand the displacement would be zero, since displacement is defined as the distance an object is from its starting point.

However using the equation s = {ut+{1over 2}at^2} can be shortened to h = {ut-{1over2} gt^2} to calculate overall vertical height meaning time is an important factor in the calculation. g is the acceleration caused by gravity which stays constant at approximately 9.8 text{m}/text{s}^2, depending on the direction the object is travelling a negative sign or positive sign is required since it is an equation of motion and is a vector quantity.

See also


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