rigid_body_forces_and_impulses

In addition to gravity, it is possible to add custom forces (or torques) or apply impulses (or torque impulses) to dynamic rigid-bodies in order to make them move in specific ways. Forces affect the rigid-body's acceleration whereas impulses affect the rigid-body's velocity. They are both based on the familiar equations:

• Forces: the acceleration change is equal to the force divided by the mass: $\Delta{}a = m^{-1}f$
• Impulses: the velocity change is equal to the impulse divided by the mass: $\Delta{}v = m^{-1}i$

Forces can be added, and impulses can be applied, to a rigid-body after it has been createdwhen it is created or after its creationafter it has been created. Added forces are persistent across simulation steps, and can be cleared manually.

Example 2D

let rigid_body = rigid_body_set.get_mut(rigid_body_handle).unwrap();

// The `true` argument makes sure the rigid-body is awake.
rigid_body.reset_forces(true); // Reset the forces to zero.
rigid_body.reset_torques(true); // Reset the torques to zero.
rigid_body.add_force(vector![0.0, 1000.0], true);
rigid_body.add_torque(100.0, true);
rigid_body.add_force_at_point(vector![0.0, 1000.0], point![1.0, 2.0], true);

rigid_body.apply_impulse(vector![0.0, 1000.0], true);
rigid_body.apply_torque_impulse(100.0, true);
rigid_body.apply_impulse_at_point(vector![0.0, 1000.0], point![1.0, 2.0], true);

Example 3D

let rigid_body = rigid_body_set.get_mut(rigid_body_handle).unwrap();

// The `true` argument makes sure the rigid-body is awake.
rigid_body.reset_forces(true); // Reset the forces to zero.
rigid_body.reset_torques(true); // Reset the torques to zero.
rigid_body.add_force(vector![0.0, 1000.0, 0.0], true);
rigid_body.add_torque(vector![100.0, 0.0, 0.0], true);
rigid_body.add_force_at_point(vector![0.0, 1000.0, 0.0], point![1.0, 2.0, 3.0], true);

rigid_body.apply_impulse(vector![0.0, 1000.0, 0.0], true);
rigid_body.apply_torque_impulse(vector![100.0, 0.0, 0.0], true);
rigid_body.apply_impulse_at_point(vector![0.0, 1000.0, 0.0], point![1.0, 2.0, 3.0], true);

Example 2D

commands
    .spawn(RigidBody::Dynamic)
    .insert(ExternalForce {
        force: Vec2::new(1000.0, 2000.0),
        torque: 140.0,
    })
    .insert(ExternalImpulse {
        impulse: Vec2::new(100.0, 200.0),
        torque_impulse: 14.0,
    });

/* Apply forces and impulses inside of a system. */
fn apply_forces(
    mut ext_forces: Query<&mut ExternalForce>,
    mut ext_impulses: Query<&mut ExternalImpulse>,
) {
    // Apply forces.
    for mut ext_force in ext_forces.iter_mut() {
        ext_force.force = Vec2::new(1000.0, 2000.0);
        ext_force.torque = 0.4;
    }

    // Apply impulses.
    for mut ext_impulse in ext_impulses.iter_mut() {
        ext_impulse.impulse = Vec2::new(100.0, 200.0);
        ext_impulse.torque_impulse = 0.4;
    }
}

Example 3D

/* Apply forces when the rigid-body is created. */
commands
    .spawn(RigidBody::Dynamic)
    .insert(ExternalForce {
        force: Vec3::new(10.0, 20.0, 30.0),
        torque: Vec3::new(1.0, 2.0, 3.0),
    })
    .insert(ExternalImpulse {
        impulse: Vec3::new(1.0, 2.0, 3.0),
        torque_impulse: Vec3::new(0.1, 0.2, 0.3),
    });

/* Apply forces and impulses inside of a system. */
fn apply_forces(
    mut ext_forces: Query<&mut ExternalForce>,
    mut ext_impulses: Query<&mut ExternalImpulse>,
) {
    // Apply forces.
    for mut ext_force in ext_forces.iter_mut() {
        ext_force.force = Vec3::new(1000.0, 2000.0, 3000.0);
        ext_force.torque = Vec3::new(0.4, 0.5, 0.6);
    }

    // Apply impulses.
    for mut ext_impulse in ext_impulses.iter_mut() {
        ext_impulse.impulse = Vec3::new(100.0, 200.0, 300.0);
        ext_impulse.torque_impulse = Vec3::new(0.4, 0.5, 0.6);
    }
}

Example 2D

// The `true` argument makes sure the rigid-body is awake.
rigidBody.resetForces(true);  // Reset the forces to zero.
rigidBody.resetTorques(true); // Reset the torques to zero.
rigidBody.addForce({ x: 0.0, y: 1000.0 }, true);
rigidBody.addTorque(100.0, true);
rigidBody.addForceAtPoint({ x: 0.0, y: 1000.0 }, { x: 1.0, y: 2.0 }, true);

rigidBody.applyImpulse({ x: 0.0, y: 1000.0 }, true);
rigidBody.applyTorqueImpulse(100.0, true);
rigidBody.applyImpulseAtPoint({ x: 0.0, y: 1000.0 }, { x: 1.0, y: 2.0 }, true);

Example 3D

// The `true` argument makes sure the rigid-body is awake.
rigidBody.resetForces(true);  // Reset the forces to zero.
rigidBody.resetTorques(true); // Reset the torques to zero.
rigidBody.addForce({ x: 0.0, y: 1000.0, z: 0.0 }, true);
rigidBody.addTorque({ x: 100.0, y: 0.0, z: 0.0 }, true);
rigidBody.addForceAtPoint({ x: 0.0, y: 1000.0, z: 0.0 }, { x: 1.0, y: 2.0, z: 3.0 }, true);

rigidBody.applyImpulse({ x: 0.0, y: 1000.0, z: 0.0 }, true);
rigidBody.applyTorqueImpulse({ x: 100.0, y: 0.0, z: 0.0 }, true);
rigidBody.applyImpulseAtPoint({ x: 0.0, y: 1000.0, z: 0.0 }, { x: 1.0, y: 2.0, z: 3.0 }, true);

info

Keep in mind that a dynamic rigid-body with a zero mass won't be affected by a linear force/impulse, and a rigid-body with a zero angular inertia won't be affected by torques/torque impulses. So if your force doesn't appear to do anything, make sure that:

1. The rigid-body is dynamic.
2. It is strong enough to make the rigid-body move (try a very large value and see if it does something).
3. The rigid-body has a non-zero mass or angular inertia either because they were set explicitly, or because they were computed automatically from colliders with non-zero densities.

4. The rigid-body is awake (by waking it up manually or setting the last wake_up parameter to true).