Friction
yes, but only when the brakes are applied.
A car slowing down when the brakes are applied.
The friction caused by the brakes causes the car to decelerate. This negative acceleration, in turn, causes a force to be applied to all those in the car. This is the lurch you feel.
When the brakes are applied, the car's kinetic energy is converted to heat by friction between the brake pad and the brake disk.
Gravity
yes, that happened to me once..
you need brake pads
Hope that doesn't happen on a busy road.
Friction
Vibration when applying brakes is most likely warped rotors. Another cause could be loose caliper bolts.
It depends on the decelerating force applied by the brakes.