As I sit in my chair, I experience a gravitational force pushing me into the chair and I'm also experiencing the normal force of the chair pushing back at me so I don't fall. According to Newton's Laws, $F=ma$ and I understand that gravitational acceleration near Earth is $-9.8\: \mathrm{m/s^2}$ so the normal force is $9.8\: \mathrm{m/s^2}$ times my mass.
What I don't understand is that if acceleration is change in velocity and my velocity is not changing (thus acceleration is zero), how is there a force?
Best Answer
You just need to be careful about the distinction between certain individual interactions (forces), and the net force on your body.
Newton's Second Law demands that the net force on your body is your mass times your acceleration. Your acceleration is zero when you're sitting still on Earth because the net force on your body is zero; the gravitational force pulling you downward balances the normal force of the ground pushing you upward. This does not mean that you can't feel the the normal force itself.
You will be able to feel any such contact force, even if the total force on your body is zero.