Ola Gabrielsson asked:
Dear Naked Scientist!
I live in Jersey, Channel Islands, where we have some of the highest tides in the world. Sometimes 12 metres on a spring tide.
I can understand the reasons for the tides; the influences of the sun and the moon but one thing that has escaped me is why there are 2 high tides (and obviously 2 low) every 24 hours.
Every point on earth spins round the earth axis once in 24 hours so why is there a 'bulge' on the far side as well as the side towards the moon/sun?
Remember the comet Schumacher-Levy that split into a string of chunks as it went past Jupiter before crashing into the same planet later on? Well, it was pulled out into a string of chunks by the gravitational pull on it which was stronger at one side than the other due to one side being nearer to the source of gravity. The same kind of thing happens when entering a black hole - even small things which are strongly held together get spaghettified by the different strength of gravity across them in such an extreme environment. The moon (and sun to a lesser degree) are also trying to pull the earth into a string in the same way, but the Earth's gravity is far too strong to let that happen. Even so, it will distort, but it's rotating too quickly for those distortions to get very far because of the solid surface and deeper stodgy material of the planet. The water on the surface, however, is able to move more freely and forms a bulge on the side nearest the moon, plus another bulge on the opposite side where the gravity from the moon is weakest - these bulges are lumps of water which are temporarily trying to follow a different orbit from the Earth as a whole.