If the object is moving in one dimension (only forward and backward), the velocity is equal to the derivative of displacement with respect to time (ds/dt).

If the motion of an object is multidimensional (for example, the curve motion in the three-dimensional space xyz), the displacement of the object changes in three directions, and the velocity is also the vector synthesis (dx/dt+dy/t+dz/dt) of the time derivative of the displacement in the three directions in space.

In order to describe accurately, the potential vector is introduced, and the displacement is also regarded as a vector in three directions.

* * * The following are additional concepts for reference only * * *

If it is a four-dimensional space (assuming that the fourth dimension is called time t for short), besides the displacement change of the three-dimensional space, the object may have a fourth movement mode: under the condition that xyz is unchanged (the three-dimensional space is static), the object suddenly disappears and appears, or (that is, when the time and space where the observer is located coincide with the t dimension of the time and space where the object is located, the object is now visible, otherwise it is invisible. The object is in the past or in the future) and presents different states (for example, from the birth of t 1v 1 to the growth of t2v2 to the extinction of t3v3). Because of the contradiction in the derivative of time (dt/dt), the velocity of three-dimensional objects is obviously not applicable to the definition of four-dimensional space. The T-dimensional motion of a four-dimensional object in time and space can be defined as the dislocation of the original time axis of the object in different States. How to understand this definition: If the observer appears before the birth of the object (t 1v 1), the observer can't see the object, and then the object moves (the time axis is misaligned, that is, time flies) so that t2v2 just coincides with the time and space where the observer is, then the observer can see an object with the size of v2 (the growth stage of the object V2). If the object continues to move in the original direction, if t3 is before the observer's time and space, the object will disappear in the observer's space again, because when the observer begins to observe, the object is dead, but in time and space, the object still exists.

There are more moving objects in the dimension, so students can spread their thinking and keep exploring.