Foucault Pendulum, School of Physics, UNSW, Kensington, NSW
Posted by: Groundspeak Premium Member Grahame Cookie
S 33° 55.112 E 151° 13.813
56H E 336398 N 6245466
Quick Description: This one was 'under maintenance' when I stopped by the School of Physics, at the University of New South Wales, Kensington, NSW in June 2017.
Location: New South Wales, Australia
Date Posted: 6/15/2017 6:46:55 PM
Waymark Code: WMVZCH
Published By: Groundspeak Premium Member TitusLlewelyn
Views: 3

Long Description:
A physics student that was passing by mentioned that it was thought some students had tried adding their own weight to the ball to see how it would swing, so the ball had been recently removed. The floor and wall of the stairwell has been recently painted, and those tools were still blocking the way to the observation ring. There was no ball or wire. While there was no wire, the height of that part of the stairwell is about 10 metres high. From photographs it looks like the ball could be 30 cm in diameter.

Easiest access is from Gate 14 on Barker Street, and you are looking for building K15 - The School of Physics.

There is a sign/poster in the stairwell that reads:
"THE FOUCAULT PENDULUM
How to use this Foucault pendulum
[Several photos to assist interpretation]
Kneel down near the sign on the floor
Hold the ball gently against the rail with the finger tips on both hands.

Very carefully line up:
- the wire of the pendulum
- the wire under the rail of the stairs,
- the metal line on the wall
All three should lie in one plane.

Release the ball
Check that the pendulum wire swings in the plane of the fixed wire and the distant line. In not, start again.

What is a Foucault pendulum for?
Does the earth turn, as Aristarchus of Samos (third century BC) had argued? Or does the sun go round the earth as Hipparchus (second century BC) and Ptolemy (second century AD) proposed? In 1851, Jean-Bernard-Leon Foucault (pronounced fooco) suspended a long pendulum in the Pantheon in Paris to demonstrate that the earth turns.
Imagine that we set up a pendulum at the South pole: if the earth were turning, someone on the pendulum would see the earth turn clockwise. On earth, we should see the pendulum's plane turn slowly anticlockwise.

What does the pendulum do?
Here are two photographs of our pendulum taken one hour apart.
The pendulum plane looks to have rotated anticlockwise.
The procession of the plane takes a long time: at the Latitude of Sydney (34°S), it takes (24 hours)/(sine 34°) = 43 hours to make one full circle.
So it takes 7 minutes to process 1°. However, if you line up the swing carefully, you can see a difference of 1°.

If the earth turns, why don't we feel it?
We don't feel speed, we feel acceleration and forces. The earth turns very slowly - only once per day - and we turn with it. The (centripetal) acceleration involved in turning with earth is 28 mm/s, which is much smaller than that sue to gravity, which is 9,800 mm/s. The size of the force required to keep you turning with the earth is only 0.3% of your weight and, because it is nearly constant, you don't feel it.

With respect to what is the earth turning?
The frame of reference in which the simple laws of mechanics hold (an inertial frame) is also the frame in which distant galaxies are not rotating about the earth. Why this should be so is an interesting (and not entirely resolved) question.

There is much more detail on our website. Or, search for "Physclips"

There is a smaller [SAFETY] sign on the floor, at the edge of the ring, which reads:
"Safety:
"Do not put your head over the pendulum. Do not step inside the ring. Do not put part of your body under the pendulum. Do not ride on the pendulum. The ball is heavy and the wire under high tension; if it breaks it could hurt you.

"How to use it:
"Very carefully line up
- the wire of the pendulum
- the wire under the rail of the stairs
- the metal line on the wall
All three should lie in one plane

"Pull the ball to the rail with the hook, then hold it between you fingertips.

"The pendulum precesses at 1° in seven minutes. If you have lined yo the swing carefully enough, you can observe the precession after five minutes or so. Meanwhile, take the time to read the poster behind."

Visited: 1500, Thursday, 15 June, 2017
Length: 30

Material: 'Plastic'

Rotation time: 43

Hours of Operation: From: 8:00 AM To: 5:00 PM

Admission Cost: 0.00 (listed in local currency)

Weight of the ball: Not Listed

Period of oscillation: Not Listed

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