Because many fuels are fossil fuels they take millions of years to form and the known reserves are being used much faster than the new ones being made
If she only has 21 buttons and all 21 of them are large, then all of her buttons are large. so 100% of the buttons would be large.
The acceleration which is gained by an object because of the gravitational force is called its acceleration due to gravity. Its SI unit is m/s2. Acceleration due to gravity is a vector, which means it has both a magnitude and a direction. The formula is ‘the change in velocity= gravity x time’ The acceleration due to gravity at the surface of Earth is represented as g. It has a standard value defined as 9.80665 m/s2.[1]
You get the net force acting on it ... the sum of the strengths and directions
of all the individual forces there may be.