Introduction

In this arti­cle we are going to study how to use the AddForce method of Unity's Rigid­Body class, which allows us to apply forces to GameOb­jects that have a Rigid­Body com­po­nent assigned to them. The goal is to make the ball in the GameDe­vLab bounce indef­i­nite­ly for the dura­tion of the game.

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Procedure

We are going to use the "AddForce" sta­tion, which con­sists of a dia­mond-shaped con­tain­er with a ball inside. The objec­tive is to make the ball bounce indef­i­nite­ly inside the sta­tion. To do this we must apply a force when the ball hits the bottom. 

In the hier­ar­chy we have the GameOb­ject "#7 AddForce" that con­tains all the ele­ments of the sta­tion (fig­ure 2). This GameOb­ject is also assigned the Script "AddForce­ToOb­ject".

In fig­ure 3 we see the "AddForce­ToOb­ject" com­po­nent in the inspec­tor. We can assign an object to which to apply the force, in this case is "Sphere" the ball that is inside the sta­tion. We can assign a min­i­mum and max­i­mum force val­ue to apply to the ball and the direc­tion of the force.

The Ball GameOb­ject is sim­ply a prim­i­tive sphere made in Uni­ty, it is assigned a Rigid­Body com­po­nent that gives it phys­i­cal behav­ior. The ball will be affect­ed by grav­i­ty, it will be able to col­lide with objects that Col­lid­ers have assigned and we will be able to apply forces to it.

At the base of the struc­ture we have a cylin­der-shaped GameOb­ject that has a Box Col­lid­er assigned in Trig­ger mode (fig­ure 4). It also has a script called "AddForceCol­li­sion­De­tec­tion" that will detect the ball.

Solution

When we open the "AddForce­ToOb­ject" Script for the first time we find what you see in fig­ure 6. All the para­me­ters you see in the inspec­tor are defined and it con­tains only one method called "addForce". This method is defined as pub­lic because it is the one that is going to be called when it is detect­ed that the ball has touched the ground of the structure.

The solu­tion of this exer­cise is shown below and the pur­pose of each instruc­tion is explained.

To solve this prob­lem we will require three instruc­tions. The first will define the mag­ni­tude of the force to be applied, which will be a ran­dom val­ue between the min­i­mum and max­i­mum forces.

The sec­ond instruc­tion will define the total force to apply, if you saw the video about physics, to define a force we need a mag­ni­tude and a direc­tion. For the direc­tion we use the vec­tor of three dimen­sions (class Vector3) that is seen in the inspec­tor, it is called "forceDi­rec­tion­Vec­tor". But we are not going to use it as it is writ­ten in the inspec­tor. To pre­vent that Vector3 from affect­ing the mag­ni­tude of the force we must nor­mal­ize it. We do this with the "Nor­mal­ize" method of the Vector3 class. The total force to apply will be a Vector3 called "force" which is the result of mul­ti­ply­ing the direc­tion by the magnitude.

Final­ly the third instruc­tion con­sists in apply­ing force on the object. The forces are applic­a­ble to GameOb­jects that have a Rigid­Body com­po­nent assigned, in our case we are going to apply the force on the Rigid­Body com­po­nent of the ball. We use the "Get­Com­po­nent" method to obtain the Rigid­Body com­po­nent and final­ly we exe­cute the AddForce method, pass­ing as para­me­ter the force to apply.

Conclusion

When test­ing the game, the ball rebounds indef­i­nite­ly with a ran­dom force.

To define a force we need a real val­ue for the mag­ni­tude and a vec­tor for the direc­tion in which it should be applied.

The forces act on the Rigid­Body com­po­nent of a GameObjects.