# Movement direction

## Definition

The following is just a personal point of view.

Individual believes that the direction of motion is the movement trend of the object, it can have two understandings:

1. Object instant (a certain time t or a location X) Motion direction.

2. The direction of motion within a certain time interval Δt.

The motion direction of the former is the direction of the speed (instantaneous speed) of the object, which is an instant movement trend of the object; the latter movement direction is the direction in time ΔT, it is equivalent The displacement direction with the object. The instantaneous speed is the first order derivative of the position R (in the direction from the coordinate origin pointing to a certain position): r ', (displacement δ r = r2 ) means that it is the change rate of the bit arbitrary, and the direction is not necessarily consistent with the direction of the displacement (the ratio and acceleration Speed ​​relationship). Instantaneous velocity: v = r ' = d r / dt, the moment displacement infinitesimal d instantaneous direction of motion of the object r The direction is consistent. For the movement direction of the object in ΔT, it is consistent with the displacement, which can also be obtained from the formula V = δ r / δ t t It is seen in / b>.

Thus "The direction of the speed is the direction of the movement of the object" is convincing, but we need to use a different "motion direction" with its corresponding "speed when we understand this sentence." Direction "to understand: The direction of movement in the moment is equivalent to the direction of the instantaneous speed, and the direction of movement within a period of time is equivalent to the direction of the average speed during this period (summary: the direction of motion is the speed direction).

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