Have you ever asked why an object, tossed in the air, comes back in a straight line to land on the ground?
One of the laws the world runs by is gravity, which pulls both ways between two material objects which have mass. This force gets bigger as the mass of the objects being pulled gets bigger, and smaller as the objects get farther apart from one another.
An old story tells us that one day, in the year 1669, Isaac Newton was sitting beneath an apple tree when an apple suddenly fell from the tree and landed on his head. That made him wonder why the apple had fallen, as well as about the speed it reached during the fall.
That experience, according to the story, led the famous scientist to formulate the Laws of Classical Mechanics, which have endured to this day as the foundation for our understanding of forces and movement of objects in the world.