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# Overview of Gravity and Gravitation

by Ron Kurtus (revised 15 June 2012)

Gravity and gravitation are fascinating subjects that affect us all. They are also important in the study of Physics and Astronomy.

We experience gravity in our everyday lives, since it is the attraction of objects—including our own bodies—toward the Earth. Falling objects provide a good subject for scientific measurements and experiments.

Beyond gravity is gravitation, which is the attraction of objects of mass toward each other. When objects are relatively close to the Earth, gravitation can be approximated as gravity. There are three major theories of what causes gravitation.

Gravity and gravitation equations have a number of uses and applications.

Questions you may have include:

- What is gravity?
- What is gravitation?
- What are their applications?

This lesson will answer those questions. Useful tool: Units Conversion

## Gravity

Gravity is a force that attracts objects toward the Earth. The acceleration due to gravity constant is an approximation from the gravitation equation. The force of gravity is measured as the weight of an object.

An important concept is that the acceleration due to gravity is considered constant near the Earth, such that all objects fall at the same rate. Also, horizontal motion is independent of the force of gravity.

Starting with the acceleration due to gravity constant, you can derive of gravity equations for the velocity, displacement and time that apply to objects dropped, thrown downward or projected upward. These equations allow you to verify the laws of gravity, as well as to apply them to predict such things as the displacement an artillery shell will travel and the relationship of work and gravity.

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See Overview of Force of Gravity to start the lessons on gravity.)

## Gravitation

Gravitation is the attraction between objects because of their mass. There are three major theories of what causes gravitation: *Newton’s Law of Universal Gravitation*, the *General Relativity Theory of Gravitation* and the *Quantum Theory of Gravitation*. These theories are somewhat at odds with each other. There is also the question of the effect of dark matter on gravitation.

In an effort to resolve the differences in the theories, gravitation was first compared with electromagnetic forces and then added to the list of *Fundamental Forces*.

The *Universal Gravitational Equation* provides the force of attraction between two objects. The *Cavendish Experiment* was used to measure the equation's gravitational constant.

Using the *Universal Gravitational Equation*, you can determine such things as the initial velocity required for an object to escape the gravitational pull of the Earth, Sun or other celestial bodies.

There are numerous applications of these concepts and various gravitation equations.

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See Overview of Gravitation for more about this subject.)

## Applications of gravity and gravitation

There are numerous applications from the gravity and gravitation concepts and equations.

### Gravity and energy

- Overview of Energy from Gravity
- Energy of Falling Objects
- Energy of Objects Projected Downward
- Energy of Objects Projected Upward

### Gravity applications

Applications of gravity concepts and equations include how you can:

Determine the final energy and velocity of a falling object

Predict the displacement a projectile travels before it lands

Calculate the velocity needed to send a projectile into space

Create artificial gravity

Determine how much work gravity can do

Determine how much work is required to lift an object against gravity

See how the center of gravity of an object can be used

### Gravitation applications

Applications of gravitation concepts and equations include how you can:

Measure the gravitational force between two objects

Find the center of mass of an object

Establish a circular gravitational orbit

Measure the length of year for objects in orbit

Understand how gravitation causes tides on Earth

Measure the gravitational escape velocity

## Summary

Gravity is the attraction of objects toward the Earth, such that all objects fall at the same rate. Equations for velocity, displacement and time of falling objects, as well as those projected upward or downward, can be derived.

Gravitation is the attraction of objects of mass toward each other. It can be approximated as gravity for objects relatively close to the Earth. There are three major theories of what causes gravitation.

Gravity and gravitation equations have a number of uses and applications.

Always try to exceed your capabilities

## Resources and references

### Websites

**Force of Gravity** - Universe Today Magazine

**How does gravity work?** - How Stuff Works

**Standard gravity** - Average value, as compared to variation due to position on Earth - Wikipedia

**International Gravity Formula** - Variation of gravity with displacement from equator - Geophysics dept. University of Oklahoma

**Gravitation** - Wikipedia

**Sir Isaac Newton: The Universal Law of Gravitation** - Dept. of Physics & Astronomy University of Tennessee at Knoxville

**Newton's Law of Universal Gravitation** - Wikipedia

### Books

**Top-rated books on Simple Gravity Science**

**Top-rated books on Advanced Gravity Physics**

## Questions and comments

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## Where are you now?

## Overview of Gravity and Gravitation