You keep moving because of a property of matter called Inertia.
This property was described in Sir Isaac Newton's first law of motion.
The first law of motion states: All non-moving objects will remain
non-moving and all moving objects will remain moving at the same speed
in the same direction until acted upon by an external force.
External Forces could be a push, a pull, gravity, friction, etc.
So you ride on your skateboard and the skateboard suddenly stops
because something acts upon it with a force. However, you keep moving
because nothing has acted on YOU with a net force, just on your
It's the same reason that seatbelts are on cars. If the car stops,
you'll keep moving until acted upon by a force. That could be the force
of the dashboard or windshield, or the force of the seatbelt, if you're
being a good passenger.
(republished on 07/19/06)