Final answer:
The movement where animals change their speed in random directions due to a stimulus is known as orthokinesis, a type of kinesis. It is a survival behavior that helps animals avoid unfavorable environments.
Step-by-step explanation:
The behavior the student is asking about is known as kinesis, which refers to the undirected and random movement of an animal in response to a stimulus. Specifically, orthokinesis is related to the change in speed of an animal's movement in response to a stimulus. For instance, woodlice may increase their speed when exposed to extreme temperatures. This change in speed, even though random, reduces the time the animal spends in a harmful environment. Klinokinesis, an increase in random turning behavior, is seen in organisms like E. coli and works alongside orthokinesis to help these organisms find better conditions. These behaviors ensure the animal's survival by moving them away from unfavorable environments.
Within the context of physics, random motion can also be described in terms of things like Brownian motion or a random walk, where particles suspended in a fluid move in a chaotic, random manner due to molecular collisions. However, the student's question is specifically referring to animal behavior, which is why kinesis is the correct term in this biological context.