Dr. Michael Shara, an astrophysicist from the American Museum of Natural History, says: Ever heard of Newton’s Law of Gravity? The famous mathematician Isaac Newton came up with this description of the force of gravity between two objects over 300 years ago. Today, scientists are still using it to describe the how objects move in space. For example, they use it to: • Calculate the orbits of the Space Shuttle • Predict where asteroids will cross Earth’s path • Understand why objects in space change their velocity as they do The law can be shown with the formula: What does this mean? First, let’s look at what the letters represent: F represents the gravitational force between two objects m1 and m2 represent the mass of the two objects r represents the distance between the two objects G represents a number that is constant and unchanging in the universe. Keep in mind that there’s always a gravitational pull between any two objects. Scientists use this formula to figure out how big the pull is. Newton’s Law of Gravity shows two important ideas: The more mass an object has, the greater the gravitational pull it exerts. That’s why we feel more gravity on Earth than on the Moon. The closer two objects are, the stronger the pull of gravity they exert on each other. But the pull doesn’t just increase — it’s increased by the inverse square of the distance. An object half the distance away feels a pull four times stronger. An object a third the distance away feels a pull nine times stronger. Even though the Earth’s mass is a lot smaller than the Sun’s, the Earth is much closer to us so its gravity overwhelms the Sun’s. That’s why the Earth has a much stronger pull on us than the Sun — and why we stay firmly on the ground instead of flying off! Close Window