Forces and Acceleration
As mentioned in the video, we talk about forces and accelerations interchangeably. The arrows in the video always show acceleration – the longer the arrow, the larger the acceleration. The force can be deduced by the formula F=ma. So for example the middle part of the Earth model, which is assumed to be more massive, requires larger forces for the same acceleration.
Interestingly, fictitious forces all have a property that they are proportional to the object’s mass. That is the more massive an object, the larger the fictitious force that will be applied on it. Therefore, the acceleration due to a fictitious force doesn’t depend on the object’s mass.
The same is true for gravity. The acceleration due to gravity is independent of the mass. This is one of the reasons that makes Gravity suspicious as a fictitious force also, as, to a certain extent, it is perceived in General Relativity.
In the video the gravity graph stops at the Sun, but actually we can continue it inside the Sun as well.
This is how it would look like if the Sun had uniform density, according to Shell’s theorem: