I used to work at a self-driving car company, and all the vehicle's motion was planned around how much jerk to apply. Your muscles are pretty good at applying

I used to work at a self-driving car company, and all the vehicle's motion was planned around how much jerk to apply. Your muscles are pretty good at applying a constant force (or responding to a constant acceleration). Hold your arm out straight: it's no effort to keep your arm still and counteract the force of gravity. Now imagine gravity varies quickly and randomly between 0.5g and 2g. I guarantee your arm won't stay still. The same prinicple applies on a bus or in a car, except this time the forces are smaller, and it's your neck keeping your head still!