Sounding Pipes
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### Lecture Description

A - We have a wind-chest - an air-tight box so equipped at the top that we can place pipes in holes so they can be blown simultaneously. We start with two identical pipes - identical length - identical diameter - and therefore identical pitch. We sound them together. They emit alike. Now the question: How can we change the pitch of a pipe? Answer: By various means. First we change its length with a sliding sleeve. Doing this gives rise to beats with the other pipe. The greater the difference in lengths the greater the beat frequency. If one pipe has a frequency f. and another a frequency f„ -the beat frequency will be f„ - f,. And now else can we change the pitch? By changing the medium with which the pipe sings. So we heat one pipe and beats again rise. The higher the temperature of the air in the pipe the higher the velocity of sound in the pipe and the higher the pitch.

B - We show the amazing performance of thermally-excited pipes. A metal pipe has a bit of metal screen lodged in it. We heat the screen. Re¬move the pipe from the heat source. And an enchanting thing is witnessed. The pipe sings! With the pipe held horizontally no convection can exist so no music can come out. As I like to say: The music cannot fall out when the pipe is horizontal! And further exploration of this sort-reveals what we expect: Longer pipes have lower pitch. AND - note well this detail: These metal pipes with wire screen sing AFTER they are removed from the heat source.

C - We now explore the enchanting behavior of CARDBOARD TUBES - the like of which rugs come rolled on. This I call intellectual fun! These pipes can sing while they are being energized! A whole array of these could provide a Bach choral! Are we not agreed that SINGING PIPES have enchantment abundant?

### Course Description

Demonstrations in Physics was an educational science series produced in Australia by ABC Television in 1969. The series was hosted by American scientist Julius Sumner Miller, who demonstrated experiments involving various disciplines in the world of physics. The series was also released in the United States under the title Science Demonstrations.

This program was a series of 45 shows (approximately 15 minutes each) on various topics in physics, organized into 3 units: Mechanics; Heat and Temperature / Toys; and Waves and Sound / Electricity and Magnetism.