The gravitational force is one of the *four fundamental forces* in the universe, along with electromagnetism, weak nuclear force, and strong nuclear force.

All matter in the *universe exerts gravitational force* on all other matter, although it is very weak for most substances. Gravitational force is what **keeps us grounded** on earth and what causes objects to accelerate towards each other when thrown.

Researchers use a device called a gravimeter to measure gravitational force. This device uses a laser that sends photons down **two perpendicular tunnels** that are surrounded by a floatation device. The difference in time it takes for the photon to travel down each tunnel and return to the surface indicates how much gravitational pull there is at that location.

## Determining the distance between objects

Knowing the distance between the objects is essential in calculating gravitational force. You must be able to distinguish between distance and size, as these are different terms.

Distance refers to how *far two objects* are from each other. This can be measured in many ways, including meters, miles, kilometers, and yards. It is a quantitative value that has a defined measurement system.

Size refers to the magnitude of an object. Size can be described in many ways, such as small, large, thin, thick, etc. Determining size is more subjective than determining distance.

The difficulty in determining the distance between **two gravitationally interacting bodies depends** on whether they are of similar size or not. If they are of similar size, then their distance can be determined by *using basic geometry* (i.e., the Pythagorean theorem).

## Understanding Newton’s law of universal gravitation

Newton’s law of *universal gravitation states* that every object in the universe exerts a gravitational force on every other object in the universe. The direction of the force is dependent on the relative position of the objects, and how they are positioned relative to each other.

The more mass an object has, the more gravitational force it exerts on other objects. The greater the distance between two objects, the *less gravitational force* there is between them.

As we will see in this article, it is possible to calculate how *much gravitational force one object exerts* on another given their masses and their distance apart. We will do this for *one particular example*, but you can use these principles to calculate gravitational forces for any two objects.

## Calculating the mass of objects

The mass of an object is its weight divided by the force of gravity that object experiences. In other words, mass is the amount of matter an object contains.

Because scientists use SI units, the mass of an object is measured in grams (g) or kilograms (kg). The weight of an object is how much it experiences the force of gravity, which is measured in newtons (N). One newton is equal to *one kilogram per one meter*.

You may have heard the term “**weight loss**” before, but what does that really mean? Weight loss simply means losing mass—in other words, losing kilograms.

There are some tricks to accurately determine the mass of an object, however. One way is to measure its volume and calculate how much material it contains. Then you can compare that with how much it weighs and divide the two to get its mass.

## Understanding what 1 kg represents

One kilogram is a metric unit of mass. The *word kilo refers* to 1,000 and grams refers to units of mass.

The International System of Units, or SI units, defines the kilogram as the mass of the big platinum–iridium cylinder stored at the BIPM in Paris. This is very precise!

Every country has a national prototype kilogram that it uses to determine the mass of goods. These are *compared every five years* at the BIPM to determine if any countries’ national prototypes have changed relative to the Paris kilogram.

Because these kilograms are used so frequently in trade and production, they are very well-maintained to keep them as close to one another as possible.

## Determining the dimensions of your space

Now that you know how to calculate the force of attraction between **two bodies**, you need to figure out how to use that information in your game.

The first thing you need to determine is the dimensions of your game world. How large is the space that your characters inhabit? Is it a planet, a town, a house, a room?

This is an important question to ask, because it will determine how close objects can get before they interact with each other. If the world is very small, then there is no point in calculating interactions between objects that are far apart from each other — it will just *waste processing power*.

Planning out your world ahead of time will also help with determining how gravity works in your universe. If you know that there are five planets in your *solar system* and that **one planet takes one year** to go around the sun, then you can easily calculate how long it takes for that planet to revolve around the center of mass of the solar system.

## Calculate the force of gravity using this formula

Now let’s put this formula to work. Imagine that you have a 1-kg object and you want to find the **gravitational force** (read: weight) of that object on another 1-kg object that is located 1 m away.

You can do this by **first thinking** about what the distance is in the formula: It is the distance between the objects. So, you need to find how much distance is between the objects — which is just 1 m!

Now, inputting 1 m into the above formula gives you 100 Newtons, which is what we were looking for! You now know how much gravity (or weight) one object has on another when they are only 1 m apart.

Keep in mind that this applies to objects that are only *close enough* to each other to be affecting each other’s gravity. Beyond that distance, these calculations no *longer apply* and must be re-evaluated for further distances.