[vc_row][vc_column][vc_column_text]One obvious question to ask is what keeps the ISS from crashing to Earth. \u00a0The explanation goes back to Isaac Newton, who was the first to figure out that the pull of gravity that makes an apple fall from a tree is the same force that keeps objects like the Moon in orbit around the Earth.<\/p>\n
He conducted a thought experiment in which a cannon was hauled to the top of a high mountain (see right). \u00a0A ball fired from the cannon would fall to Earth, but would travel a little further than would be expected on a flat surface because the curvature of the Earth makes the surface fall away as the ball approaches. \u00a0Adding more gunpowder to the cannon would make the ball travel further, until a point would eventually be reached when the surface of the Earth would be falling away at exactly the same rate that the ball was falling toward it, so the distance between the ball and the surface would stay constant \u2013 the ball would be in orbit.<\/p>\n
Note that such a satellite has not escaped Earth\u2019s gravity \u2013 it is that gravity that keeps it on its circular orbit. \u00a0The \u201cweightlessness\u201d experienced on a space station is because everything in it is pulled by gravity on an identical orbit around the Earth,[\/vc_column_text][vc_spacer size=”30px”][\/vc_column][\/vc_row][vc_row][vc_column][vc_single_image image=”191″ img_size=”medium” alignment=”center”][\/vc_column][\/vc_row][vc_row][vc_column][vc_spacer size=”30px”][vc_column_text]Isaac Newton\u2019s 1728 cannon thought experiment that explained how an object could be placed into orbit around the Earth if travelling at sufficient[\/vc_column_text][vc_spacer size=”30px”][\/vc_column][\/vc_row][vc_row][vc_column][vc_column_text]Near the surface of the Earth, the speed required to achieve orbit is around 27,000 km\/h, almost ten times the speed of a bullet. \u00a0Such speeds would generate huge amounts of friction within the Earth\u2019s atmosphere which would cause the orbiter to burn up, which is why satellites like the ISS have to orbit at altitudes above almost all of the atmosphere.<\/em>[\/vc_column_text][\/vc_column][\/vc_row]<\/p>\n","protected":false},"excerpt":{"rendered":" [vc_row][vc_column][vc_column_text]One obvious question to ask is what keeps the ISS from crashing to Earth. \u00a0The explanation goes back to Isaac Newton, who was the first to figure out that the pull of gravity that makes an apple fall from a tree is the same force that keeps objects like the Moon in orbit around the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"_links":{"self":[{"href":"https:\/\/crystalnebulae.co.uk\/index.php?rest_route=\/wp\/v2\/pages\/190"}],"collection":[{"href":"https:\/\/crystalnebulae.co.uk\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/crystalnebulae.co.uk\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/crystalnebulae.co.uk\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/crystalnebulae.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=190"}],"version-history":[{"count":2,"href":"https:\/\/crystalnebulae.co.uk\/index.php?rest_route=\/wp\/v2\/pages\/190\/revisions"}],"predecessor-version":[{"id":569,"href":"https:\/\/crystalnebulae.co.uk\/index.php?rest_route=\/wp\/v2\/pages\/190\/revisions\/569"}],"wp:attachment":[{"href":"https:\/\/crystalnebulae.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=190"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}