Rigidbody 3D component in Unity - Step-by-Step Execution

Concept Flow - Rigidbody 3D component

Add Rigidbody Component

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Physics Engine Controls Object

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Apply Forces or Gravity

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Object Moves According to Physics

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Check Collisions and Responses

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Update Object Position and Rotation

The Rigidbody 3D component lets Unity's physics engine control an object, moving it with forces and gravity, and handling collisions.

Execution Sample

Unity

void Start() {
  Rigidbody rb = GetComponent<Rigidbody>();
  rb.AddForce(new Vector3(0, 10, 0), ForceMode.Impulse);
}

This code gets the Rigidbody component and applies an instant upward force to make the object jump.

Execution Table

Step	Action	Rigidbody State	Position	Velocity	Output
1	Get Rigidbody component	Active	(0,0,0)	(0,0,0)	Ready to apply forces
2	Apply upward impulse force	Active	(0,0,0)	(0,10,0)	Velocity changes instantly
3	Physics update frame 1	Active	(0,0.1,0)	(0,9.02,0)	Object moves up slightly
4	Physics update frame 2	Active	(0,0.28,0)	(0,8.14,0)	Object continues moving up
5	Physics update frame 3	Active	(0,0.53,0)	(0,7.26,0)	Object slows down due to gravity
6	Physics update frame N	Active	(0,y,0)	(0,v,0)	Object eventually falls back down
7	Collision detected	Active	(0,0,0)	(0,0,0)	Object stops moving on ground

💡 Simulation continues until object stops or script disables Rigidbody

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	Final
Position	(0,0,0)	(0,0,0)	(0,0.1,0)	(0,0.28,0)	(0,0.53,0)	(0,0,0)
Velocity	(0,0,0)	(0,10,0)	(0,9.02,0)	(0,8.14,0)	(0,7.26,0)	(0,0,0)
Rigidbody State	Active	Active	Active	Active	Active	Active

Key Moments - 3 Insights

Why does the object's velocity change instantly after applying AddForce with ForceMode.Impulse?

Because ForceMode.Impulse applies an immediate change to velocity, as shown in execution_table step 2 where velocity jumps from (0,0,0) to (0,10,0).

Why does the position keep increasing even though no new forces are applied after the impulse?

Because the Rigidbody's velocity carries the object upward, and gravity gradually reduces velocity over time, seen in steps 3 to 5.

What happens when the object collides with the ground?

The Rigidbody stops moving and velocity resets to zero, as shown in step 7 where position is at ground level and velocity is (0,0,0).

Visual Quiz - 3 Questions

Look at the execution table, what is the velocity of the Rigidbody right after applying the impulse force (Step 2)?

A (0,10,0)

B (0,0,0)

C (10,0,0)

D (0,-10,0)

💡 Hint

Check the 'Velocity' column at Step 2 in the execution_table.

At which step does the Rigidbody start slowing down due to gravity?

A Step 2

B Step 5

C Step 3

D Step 7

💡 Hint

Look at the velocity values decreasing in the execution_table between steps 3 to 5.

If we remove the Rigidbody component, what would happen to the object's movement?

A It would still move with physics forces.

B It would not move due to physics.

C It would move faster.

D It would fall faster.

💡 Hint

Refer to the concept_flow where Rigidbody is needed for physics control.

Concept Snapshot

Rigidbody 3D component lets Unity physics move objects.
Add Rigidbody to object to enable physics.
Use AddForce to push or pull it.
ForceMode.Impulse changes velocity instantly.
Gravity pulls object down automatically.
Collisions stop or bounce the object.

Full Transcript

The Rigidbody 3D component in Unity allows the physics engine to control an object. When you add a Rigidbody, the object can move with forces like pushes or gravity. In the example, we get the Rigidbody component and apply an upward impulse force, which instantly changes the object's velocity upwards. Each physics update moves the object according to velocity and gravity slows it down over time. Eventually, the object collides with the ground and stops moving. This shows how Rigidbody handles movement and collisions automatically.