What happens to a liquid in a swing or a loop? Accelerated motions lead to effects that may seem
surprising. Consider a liquid in a glass placed on a wooden triangle, in turn attached to a string
and moving fast in circle a vertical plane. The surface of the water remains parallel to the bottom
of the glass—and orthogonal to the string—as long as gravity and the tension in the string are the
only forces acting on the triangle. A key to the understanding is that the tangential acceleration
of the liquid, the glass and the triangle, are all identical to the tangential component of the
acceleration of gravity.