Actions such as pushing, pulling, stretching, hitting, compressing and lifting give us an idea of strength. One body can interact with the other through a contact force or distant action forces, such as the force with which the earth attracts bodies.

**A body falls because the earth pulls it down.** The fall happens even without contact between the earth and the body. We observe another similar phenomenon when we approach two magnets, sometimes they repel each other and sometimes attract each other. This occurs without contact between them. In these examples we observe the action of action forces at a distance.

Forces occur in nature in the form of contact actions or distance actions. The unit of measure of force in the international system (SI) is Newton (N).

## Adding forces

Following is an example of adding quantities.

While making a juice, Joana mixed 2 liters of water with half a liter of concentrated grape juice. What was the resulting volume of grape juice?

Being **V _{1}** the volume of water and

**V**The volume of grape juice we have:

_{2}**V _{1}** = 2L

**V _{2}** = 0.5 L

So, **V _{1}** +

**V**= 2.5 L

_{2}That is 2 and a half liters of grape juice.

When mixing the volumes of two miscible liquids, the final volume is the arithmetic sum of the volumes of each part. |

The next example shows us that the sum of vector quantities requires further analysis.

If two people push the box to the right, one pulling it with a force of 20N, and the other pushing it with a force of 10N, the sum of the two forces will be 30N. **We often refer to the sum of the resulting force forces.** The resulting force equals a single force that would act on the body, producing the same effect as all other joints.

In this example, the resulting force has 30N intensity, horizontal direction, and left to right direction.

Now, for example, if both people “pull” the box, but the person on the right pulls the box more intensely (25N) than the person on the left (10N). In this case, the resulting force is 15 N, and has a horizontal direction and a left-to-right direction.

### To find the resulting force

To find the resultant force of two forces acting on a body, one must make the following considerations:

- If the forces have the same direction and direction, the resulting force will have an intensity equal to the sum of the intensities of the initial forces and their same direction and direction.

- If the forces have the same direction and opposite directions, the resulting force will have an intensity equal to the difference of the intensities of the initial forces, the same direction of them and the direction of the force of greatest intensity.