Unity Lerp Tornado Simulation

A physics-based tornado simulation in Unity that combines linear interpolation, animated pivot rotation, and rigidbody dynamics to create a convincing vortex effect.

How It Works

The tornado effect emerges from three layered techniques:

1. Animated pivot path — An Animator drives a pivot point along a predefined trajectory
2. Rotational interpolation — A modified lerp generates a spiraling path around the moving pivot
3. Rigidbody interaction — Objects within the trigger volume are pulled in or pushed out based on their distance to the vortex center

Force Model

The core mechanic uses a custom linear interpolation remap to modulate force direction based on distance. For an object at distance $d$ from the vortex center, the interpolation scalar $t$ is computed as:

$$t = \frac{d - a}{b - a} \cdot (t_b - t_a) + t_a$$

where $a = 0$, $b = 10$, $t_a = 1$, and $t_b = 0$. This produces a value $t \in [0, 1]$ that decreases as distance increases — objects closer to the center experience stronger centripetal pull.

Direction Reversal

A threshold parameter $r$ controls the transition between pull and push behavior:

$$\vec{F} = \begin{cases} \hat{d} \cdot F_c \cdot m \cdot t & \text{if } t \leq r \[6pt] -\hat{d} \cdot F_c \cdot m \cdot F_p & \text{if } t > r \end{cases}$$

where:

• $\hat{d}$ — unit direction vector from object to vortex center
• $F_c$ — centripetal force strength
• $F_p$ — push (counter) force
• $m$ — force multiplier
• $r$ — reverse indication threshold (default: $0.8$)

This creates a pull-push cycle: objects accelerate toward the center, then get ejected outward once they cross the threshold — producing the characteristic spiraling motion of a tornado.

Parameters

Parameter	Description	Default
centripetalForce	Inward pull strength	10
push	Outward counter-force	3
forceMultiplier	Global force scalar	10
reverseIndicationValue	Distance threshold for direction flip	0.8

Controls

• Play Mode — Click the white square buttons to spawn objects into the scene
• Observe — Watch the rigidbodies interact with the vortex field

Tech Stack

• Unity — Game engine and physics (Rigidbody, Trigger Colliders)
• C# — Custom interpolation and force calculations
• Animator — Pivot path animation