Science Quiz: When sound gets on the move

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What’s the name for the part of the human ear visible outside the head? It’s called the pinna in non-human animals.

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Grains of sand on a vibrating plate often shift into precise, geometric shapes that depend on the vibrations. These patterns also change when the frequency changes. What name is given to this visualisation of sound and vibration?

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An aeroplane traveling faster than sound forces pressure waves to accumulate in front of it. When the vehicle starts to move faster than the speed of sound in that medium, a sudden explosive noise is heard. What is this dramatic event called?

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Vibrations in a guitar string or a vibrating column of air inside a pipe can sometimes ‘lock’ themselves into a stable pattern. As a result, certain points in the string or column stay still while others vibrate vigorously, creating nodes and antinodes. What are such waves called?

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When a swing is pushed at its natural frequency, it soars higher with little effort. If you push it at the wrong time, even a strong push may not lead to a big change in its motion. Bridges and glass objects have been known to shatter when they’re perturbed at their natural frequencies. Name the phenomenon that causes vibrations to amplify when stimulated at the natural frequency.

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Some artificial materials can guide or block sound in ways that nature can’t. These materials can even ‘cloak’ objects such that they don’t emit or reflect any sound. What are such advanced materials called? Hint: Their name means “subsequent to” or “after” materials.