What kind of engine do we need to make a spacecraft travel at 28000 kilometres an hour? Ordinary engines, like the petrol engine used in cars, are not powerful enough by half. Nor are the jet engines used in aircraft. Even the fastest jet planes

What happens when you jump up into the air? You will definitely come back to ground. It is only because of Earth that a jumper when it goes up comes back on the ground. What happens when an apple is ripe? It falls from the tree down to the ground.