AQA 

CCEA

 Edexcel 

 OCR A 

 OCR B 

WJEC

CIE

Edexcel

1

Sound Waves

These longitudinal waves that humans can detect have a frequency between 20 and 20,000 Hz.

(At 4:27 I should have said solids and liquids are denser so they travel quicker in these materials)

2

Echo Sounding in Deep Water

How fishermen detect fish and submarines don't bump into the sea floor. 

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AQA

CCEA

Edexcel

OCR A

OCR B

WJEC

CIE

Edexcel

or