There is a saying, 'What goes up must come down.' Thats the law of gravity. A famous scientist called Sir Isaac Newton was the first person to understand gravity. What do you think our world be like without gravity? How would you move?There is a saying, 'What goes up must come down.' Thats the law of gravity. A famous scientist called Sir Isaac Newton was the first person to understand gravity. What do you think our world be like without gravity? How would you move?