As water is heated, dissolved gasses in the water start to come out of solution. As water approaches boiling point all the dissolved gases have been released so there is no more bubbling. This is when the kettle goes quiet. As the water then begins to boil, the convection currents in the water become very violent and the water becomes noisy again.
Q Why doesn't lightning affect people inside a car?
There's a special effect in a hollow sphere of metal, called a Faraday Sphere, where there isn't any electricity inside the sphere. Faraday, the man who came up with lots of the rules on electricity which we now use, first found out that a hollow sphere has no electricity in it.
Q If a pineapple is a fruit, where are its seeds?
The pineapples eaten today are different from wild pineapples still found in some countries. A pineapple is a compound fruit - it is made up of several sections all stuck together to make one bigger fruit. Each section has its own seeds buried beneath the skin in sacks. If you peel a cultivated pineapple, you can sometimes see the vaguest hint of the seeds that a cultivated pineapple's "ancestors" would have had. In the past, someone must have found a pineapple without seeds that was managing to reproduce itself. This pineapple would have been produced accidentally by nature but, because there are no seeds, each pineapple has more fruit and is therefore more valuable to us. Farmers figured out that they could earn more by growing these types and so grew nothing else, so pineapples with seeds are now very rare.
Q What is hair made of?
Hair is made from cells called epithelial cells which are arranged in three layers. The innermost layer is the medulla, the middle layer is the cortex and the outer layer is the cuticle. The medulla is mainly soft keratin (a protein) and the cortex and cuticle are mainly hard keratin. This structure is very strong making a strand of hair tougher than an equally thick strand of nylon or copper wire.
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