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If the world is moving, why wouldn’t we fall off the edge of a cliff?

If the world is a sphere would it mean when we approached a cliff face, then the world moved, would we fall off the edge?
Melissa Devenish from Somerset (Aged 15-25)

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2 Responses

  1. The world is moving(rotating). The good thing is that we are also moving at the same speed(because we are standing on it). Therefore we do not notice the huge speed that we are spinning at.

    We would notice if the earth slowed a bit or got a bit faster. This is unlikely to be a big change because the earth is so massive. So if we approached a cliff face and the Earth changed its speed of rotation, we would stumble or wobble on our feet. The same thing happens if we are stnading in a bus or train when it speeds up or slows down. We have to adjust to the speed change.

    Once we and the bus are moving at a steady speed we are quite stable. So back to the earth rotating. Because the earth is rotating at a constant rate, it feels quite stable to us. We notice speed changes(acceleration or deceleration) we do not notice speed istelf. Traveling in Concord(1200 mph) feels the same as traveling on a bus(30 mph) and feels the same a standing still. We notice if the bus speeds up or slows down.

  2. Just to add to the answer below that your concern was quite common in the 16th and early 17th century, when the Earth’s position in the Universe and movements were beginning to be understood.

    At that point, one of the main arguments of the opponents to the idea that the Sun is at the centre of the Universe and the Earth wanders around it (defended, among others, by Copernicus and Galileo) was that, if the Earth moved, we would falling all the time and if, for instance, we dropped a pencil, it wouldn’t fall following a straight line.

    With the formulation of Gravity Theory by Isaac Newton in the late 17th century, this problem was greatly solved: bodies are attracted towards the centre of the Earth and that’s why they fall, approximately, towards the same place independently of the Earth’s movement.

    Miguel Garcia-Sancho
    Centre for the History of Science
    University of Manchester
    http://www.chstm.manchester.ac.uk

    Look at my articles at
    http://www.hss.ed.ac.uk/genomics/vol2no3/Garcia-sanchoabstract.htm.
    and
    http://dx.doi.org/10.1016/j.endeavour.2007.01.006

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