Rigidbodies & Forces

Rigidbodies & Forces

Unity includes a built-in 3D and 2D physics engine. To make a GameObject behave physically, you need a Rigidbody component.

Rigidbody Component

The Rigidbody component puts a GameObject under the control of Unity's physics engine.

• Gravity: Checking "Use Gravity" makes the object fall down.
• Mass: Defines the weight of the object (higher mass resists force more).
• Drag: Air resistance that slows down movement or rotation.
• Is Kinematic: If checked, the object is NOT affected by forces, gravity, or collisions. It can only be moved manually via script or animation.

Applying Forces in C#

To move a Rigidbody physically, do not set its transform position directly. Instead, apply forces:

private Rigidbody rb;

void Start()
{
    rb = GetComponent<Rigidbody>();
}

void FixedUpdate()
{
    // Apply upward force
    rb.AddForce(Vector3.up * 10f, ForceMode.Force);
}

ForceModes

The ForceMode parameter defines how the force is applied:

• Force: Applies a continuous force, using the object's mass (ideal for wind or thrusters).
• Acceleration: Applies a continuous acceleration, ignoring the object's mass.
• Impulse: Applies an instant force, using the object's mass (ideal for explosions or jumps).
• VelocityChange: Applies an instant velocity change, ignoring the object's mass.

TL;DR

• A Rigidbody enables physics forces, velocity, and gravity.
• Kinematic Rigidbodies are immune to physics forces.
• Use rb.AddForce inside FixedUpdate for physics movements.
• Select different ForceModes depending on whether the action is continuous or instant.