I want to add jump momentum in my game, so where if I jump forwards, and can’t immediately turn in mid air. How would I do that?
You would detect a jump button press and use the AddForce function to apply a jumping force upwards (you could also set the velocity’s up component, depending on what behaviour you want when the rigidbody has downward velocity.
When you press movement keys, you should also apply a force using AddForce, instead of setting velocity directly.
If you want movement acceleration to be slower in air, you should do a raycast directly down from the rigidbody GameObject and detect the length of the raycast until it hits the floor. If that length is less than a certain height, your GameObject is on the floor, and the movement buttons should apply more force.