Universal gravitation is one of the four fundamental forces in nature. It describes the attractive force between any two objects that have mass. This force is what keeps our feet on the ground, causes apples to fall from trees, and governs the motion of planets around the sun.
Newton's Law of Universal Gravitation states that every particle attracts every other particle with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. The formula is F equals G times m1 times m2 divided by r squared, where G is the gravitational constant.
The gravitational constant G is a fundamental constant that appears in Newton's law. Its value is approximately 6.674 times 10 to the minus 11 Newton meters squared per kilogram squared. This tiny number shows that gravity is actually a very weak force. For example, the gravitational force between Earth and Moon is about 1.98 times 10 to the 20th Newtons.
Universal gravitation explains how planets orbit the sun. The gravitational force between the sun and a planet provides the centripetal force needed to keep the planet in its elliptical orbit. The red arrow shows the gravitational force always pointing toward the sun, while the green arrow shows the planet's velocity tangent to the orbit. This relationship follows Kepler's third law, where the square of the orbital period is proportional to the cube of the orbital radius.
Universal gravitation has countless applications in our modern world. It helps us predict satellite orbits for GPS systems, understand ocean tides caused by the moon's gravity, and calculate the escape velocities needed for spacecraft to leave Earth. From the simple fall of an apple to the complex dance of galaxies, universal gravitation governs the motion of all matter in the universe, making it one of the most important discoveries in physics.