Twist Scooter

There is a type of three wheeled scooter with a handlebar extending vertically upward from the apex of a V-shaped horizontal metal frame that has three wheels. The front wheel can rotate about a vertical axis at the foot of the vertical handlebar at the apex

intersection, and the two rear wheels are at the ends of the arms of the V. The two arms of the V are hinged at their intersection at the front of the scooter so they can rotate about the vertical axis of the hinge that is, they can form a wider or a narrower V angle within limits. The rider places one foot on each arm of the V and swivels his or her body from side to side to tilt the vertical handlebar from side to side to make the vehicle go forward or backward. Can you explain the physics of its forward motion?

Answer

If the plane of the V arms of the twist bike remained horizontal at all times, there would be no forward motion except by pushing with a foot on the ground. By tilting the vertical shaft of the handlebar sideways about 10 degrees or so, the front of the scooter is lowered a bit, and a slight unbalanced outward push of the arms of the V by the rider’s legs provides a forward net force similar to the resulting net force exercised by an ice skater. The initial forward movement from rest may be difficult on an upslope exceeding a particular angle determined by the size of the wheels and by the possible tip angle of the handlebar.