before designers can build a cloud propeller they have to understand why it makes so much noise if a propeller spins quickly it leaves a trail of bubbles behind it as the bubbles pop they make a lot of noise [Music] bubbles are not filled with air but with steam the steam is produced by the sea water boiling [Music] it is a well-known fact that water boils at 100 degrees Centigrade however few people will know that at different pressures the water will boil at different temperatures if you increase the pressure as in a pressure cooker for instance
then the boiling point of the water increases hence the cooking is more efficient few people will know however that at reduced pressures water will boil at lower temperatures I have here a vacuum pump and I'm going to turn on the vacuum this flask here contains water and we have it connected to a pressure gauge and we're reading at the moment approximately 15 pounds per square inch which is one atmosphere I turn on the pump do you notice the pressure dropping immediately and as the pressure drops as we approach zero bubble start to form and the
water starts to boil so here we are at room temperature but at a significantly reduced pressure almost almost the complete vacuum the water isn't now boiling water boiling at 20 degrees centigrade at almost zero pounds per square inch a remarkable phenomenon sir when a submarine's propeller turns quickly an area of low pressure is created on the blades this lowering of pressure causes the water to boil without heating up and produces bubbles of steam this is called cavitation [Music]
