Final answer:
The arrows v1, v2, etc., represent velocity vectors in a diagram of motion, showing the separate horizontal and vertical velocities at equal time intervals and highlight the independence of vertical and horizontal components in projectile motion.
Step-by-step explanation:
In physics, the arrows v1, v2, and so on, represent velocity vectors at different points along the path of an object's motion. These arrows are separated by equal time intervals, which suggest that they are showing the velocity of the object at each of those evenly spaced instants in time. In the context of two-dimensional motion, these velocity vectors can be used to illustrate both the horizontal and vertical components of the motion. The horizontal component might be constant if no external force acts on it, while the vertical component changes due to gravity.
An important concept demonstrated by these diagrams is that the vertical and horizontal motions of projectiles are independent of each other. This is why two identical balls, one with initial horizontal velocity and one without, will have identical vertical motions. The one with horizontal velocity simply moves sideways as it falls. Calculating vector magnitudes in two dimensions often involves vector addition and can require the use of the Pythagorean theorem, given the vectors are perpendicular to each other.