What is the main point that all of these videos are trying to show?

Newton's 2nd law- F=MA

Explanation:

This may be the completely wrong answer but judging by the pictures this was the car experiment where you add different weights to the car, raise or lower the ramp, and add different parachutes to experiment with how changing mass and height can affect the distance the car goes

in simple terms, the principle states that the buoyancy force on an object is equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume times the gravitational acceleration, g. this is also known as upthrust.