Motion Forces
In Babylon.js, motion forces are influences applied to a physics body that affect its motion, such as gravity, friction, and user-defined forces. They can act continuously (e.g., wind, propulsion) or instantaneously (e.g., explosions, collisions), enabling realistic physics interactions.
The two primary types of motion forces are:
Forces
A force is a continuous effect that is applied to an object over time, with can change the object’s velocity or direction of motion (gravity, wind resistance, player pushing an object).
In this example, a vortex is simulated using the Physics Helper. Click on the scene to activate the vortex at the center and watch as it moves the leaves around.
// create a leaf and define its physics
<mesh name='leaf'>
<physicsAggregate type={PhysicsShapeType.CONVEX_HULL} _options={{ mass: 0.001 }} />
</mesh>
// create 200 instances of the leaf
new Array(200).fill(null).map((_, index) => {
const name = `leaf-${index}`;
const position = new Vector3(Scalar.RandomRange(rangeX.min, rangeX.max), Scalar.RandomRange(rangeY.min, rangeY.max), Scalar.RandomRange(rangeZ.min, rangeZ.max));
return (
<mesh name={name} key={name} instanceFrom='leaf' position={position} />
)
})
// create the vortex in the center of the scene
const event = physicsHelper.vortex(
vortexOrigin: new Vector3(0, 0, 0),
{ radius: 2, strength: 0.02, height: 1, updraftForceMultiplier: 0.1 }
);
event.enable();
Impulses
An impulse is a sudden, instantaneous effect that changes the velocity of an object. It is a specific amount of force applied over a very short duration of time, often modeled as a single frame in a game. For example, a collision between two objects might generate an impulse that changes the direction and speed of both objects.
In this example, a bowling game is simulated. Click on the scene to position yourself for the launch, then click on the sphere to throw it! Did you get a strike?
// create a pin and define its physics
<mesh name='bowling-pin'>
<physicsAggregate type={PhysicsShapeType.CYLINDER} _options={{ mass: 1.6 }} />
</mesh>
// create pins instances of the pin
pinPositions.map(([x, z], index) => {
const name = `bowling-pin-${index}`;
const position = new Vector3(x * DISTANCE_BETWEEN_PINS, 0, -z * DISTANCE_BETWEEN_PINS);
return (
<mesh ref={(ref) => { pinsRefs.current[index] = ref }} name={name} key={name} instanceFrom='bowling-pin' position={position} />
)
})
// create ball, add physics and apply impulse on pick
<sphere name='ball' options={{ diameter: 0.22 }} positionZ={-4}
onPick={(event) => {
const ball = event.source as Mesh;
ball.physicsBody!.applyImpulse(new Vector3(0, -10, 50), ball.absolutePosition);
}}>
<physicsAggregate type={PhysicsShapeType.SPHERE} _options={{ mass: 6 }} />
</sphere>Learn More
For advanced use cases and customizations, please refer to Babylon.js documentation: https://doc.babylonjs.com/features/featuresDeepDive/physics/forces/.
