In physics, △ is often used as the prefix of variables, indicating the changes of variables, such as △t (time change), △T (temperature change), △X (displacement change), △v (speed change) and so on.
Generally speaking, △t=t 1-t2, etc. , t 1 and t2 can be found in the question.
△t does not necessarily mean a small quantity (as do other physical quantities), but it can mean the variation in an area.
Extended data:
The ratio of △v (speed change) to time is acceleration. Acceleration is a vector with both magnitude and direction. (Direction is indicated by+and-) The magnitude of acceleration is equal to the change of speed in unit time; The direction of acceleration is always the same as the direction of velocity change Δ v.
Especially in linear motion, if the direction of acceleration is the same as the speed, the speed will increase; The acceleration direction is opposite to the speed, and the speed decreases. Acceleration is equal to the first derivative of velocity time and the second derivative of displacement time.
1. When the included angle between the speed direction of a moving object and the acceleration (or resultant force) direction is less than 90, the speed will increase and the speed direction will change;
2. When the included angle between the speed direction of the moving object and the acceleration (or external force) direction is greater than 90 and less than or equal to180, the speed decreases and the direction changes;
3. When the angle between the speed and direction of a moving object and the direction of acceleration (or resultant force) is equal to 90, the speed is constant and the direction changes.
References:
Baidu encyclopedia-acceleration