# Gravity

## Contents

## Explanation[edit]

Gravity is the weakest of the four fundamental forces of nature. Gravity is what attracts all the planetary bodies to one another. According to Newton, Gravity is a force that attracts any two point masses in the universe. This force is directly proportional to the product of the masses and inversely proportional to the square of the distance between them. Though this holds as a good approximation, the notion of Gravity can be better understood with the help of general relativity, which describes gravity as a curvature in spacetime.

## Frequently Asked Questions[edit]

### What is the difference between mass and weight?[edit]

Mass is the amount of matter contained in a body or object. Mass is constant. Weight on the other hand, is the amount of force exerted on an object due to gravity. Unlike mass, this varies with different gravitational fields.

### What is a gravitational time dilation?[edit]

Consider two observers with identical clocks, living in two different gravitational fields, one stronger and the other weaker. When an observer from the weaker gravitational field looks at the clock in the stronger gravitational field, that clock will be ticking at a slower rate than his own clock. On the other hand, for the observer in the stronger field, he will observe that the clock in the weaker gravitational field ticking faster than his. This phenomenon is known as gravitational time dilation. A more practical example can be found in the clocks of the GPS satellites, where they tick slightly faster than the clocks at the Earth.

### How does gravity affect time?[edit]

Consider the above example in the gravitational time dilation question. Assume that the two clocks are light clocks that measure time by measuring the number of times the light bounces off the mirrors. As gravity is nothing but a curvature of spacetime, a clock at a weaker gravitational field will have a less curvature locally, when compared to the curvature around the clock at a stronger gravitational field. Light always travels at the same speed. speed = distance/time. In the stronger gravitational field, the distance is increased due to the curvature, thereby increasing the time light would take to reach the mirror. When the observer at a weaker gravitational field observes this clock, it would appear that the clock is ticking slowly relative to his clock.