Question

Why is it not possible to sit upright in a chair and rise to your feet without
first leaning forward?

Answer 1

Standing requires the feet to be under the center of gravity. While sitting, your center of gravity is too far to the rear. When you lean forward, the center of gravity is shifted forward and thus, you can easily stand up without falling.

Answer 2

Cool, i was interested in this as well

Answer 3

you can sit upright in a chair and rise to your feet without leaning forward first. .... as long as the chair is heavy enough for you to use if for leverage.