It is possible she's masturbating, but.... I would first be inclined to think she's bored. A lot of people cross their knees and jiggle the dangling leg, from nervousness, boredom, etc. But that's hard to do at a student desk. However, her choice of how to express her boredom, nervousness, frustration isn't the best choice in a roomful of people. Perhaps you could mention to your teacher or school nurse in private that the girl's movements are distracting, and the teacher can take the girl aside. The girl could need some education about what's appropriate/not, especially if she's wearing a skirt. (By the way, girls in my grade school class used to do this on very hot days....get some air under the uniform fabric to help cool off.... seriously. We didn't have air conditioned rooms, so it was often 80-100 degrees in classrooms.)
Just ignore her, by the way.
Kinetic energy moves back and forth. This is the energy associated with the motion of an object. For example, a swinging pendulum or a vibrating guitar string demonstrate kinetic energy moving back and forth.
something moves back and forth
A pendulum swings back and forth rapidly due to gravity and inertia.
It is called vibrations.
Electromagnetic energy moves back and forth between the Earth and the Sun through radiation. This energy is responsible for heating the Earth's surface and driving atmospheric processes.
then the egg will most likely being moving back and forth as well, especially if the chick is almost ready to be hatched
A tool called a jigsaw is used to make precise cuts in metal, with a blade that moves back and forth rapidly.
The head.
A vibrating object, such as a guitar string or vocal cords, moves back and forth rapidly to produce sound waves. The vibration creates changes in air pressure, which our ears detect as sound when they reach them.
Swinging back and forth on a swing involves periodic motion, specifically oscillatory motion. The motion repeats in a regular pattern as the swing moves back and forth around a fixed point.
A swinging pendulum is an example of oscillating motion. As the pendulum swings back and forth, it moves in a repetitive pattern around a fixed point. This motion is characterized by a constant cycle of movement back and forth.
A pendulum moves with only one movement, swinging back and forth in a repetitive motion.