Question

What two forces are in balance inside the Sun?

Answer 1

Hydrostatic Equilibrium, a balance between pressure and gravity.

Inward force of gravity is equal to the outward force of pressure created by fusion. When all the lighter elements have been used up (the hydrogen and helium mostly) the fusion of heavier elements will create more pressure than the force of gravity and then the sun will go nova.

Answer 2

Answer:

Balanced Forces

But what exactly is meant by the phrase unbalanced force? What is an unbalanced force? In pursuit of an answer, we will first consider a physics book at rest on a tabletop. There are two forces acting upon the book. One force - the Earth's gravitational pull - exerts a downward force. The other force - the push of the table on the book (sometimes referred to as a normal force) - pushes upward on the book.

Unbalanced Forces

Now consider a book sliding from left to right across a tabletop. Sometime in the prior history of the book, it may have been given a shove and set in motion from a rest position. Or perhaps it acquired its motion by sliding down an incline from an elevated position. Whatever the case, our focus is not upon the history of the book but rather upon the current situation of a book sliding to the right across a tabletop. The book is in motion and at the moment there is no one pushing it to the right.

Explanation: