Physics Demo Number: 167

Approximate

Run Time: 5 min

Flattening of Earth at Poles Modeled with Spinning “Centrifugal” Hoops

Demo Description

Two brass hoops are mounted on a vertical rod in such a way that they are fixed rigidly to the rod at their base, but free to slide up and down the rod at their tops.

More precisely ,two long flexible strips of brass have each been manufactured with a round hole at both ends and a round hole at their center points.

The two strips have each been formed into circles, with their three holes aligned along a diameter and placed on the vertical rod, so that the two circular planes are at right angles to each other.

The four strip ends have been placed between two lock nuts on the bottom end of the rod, but the top end of the rod is smooth so that the center of each strip can slide up and down freely on the rod.

Now the base of the rod is clamped into a chuck which can be rotated rapidly.

The hoop tops are observed to slide downwards on the rod under the dynamic state of rotary motion.

Scientific Principles

• Dynamic flattening occurs for a flexible sphere along its axis of rotation for appropriate spin rates.

Equipment

• Rod-hoop configuration of two flexible brass strips

• Drill motor for hand-held spinning of the hoops

Equipment Location

• Kit (167) on [F-1-2] houses the Rod-hoop configuration and drill motor .

Instructions

The first photo shows the hoops in a mechanical rotator and flattened at the poles.

They are flattened since they were actually spinning quite rapidly when the photo was snapped. The next picture was snapped while the hoops were not rotating,