llApplyImpulse

void llApplyImpulse(vector Force, integer Local)

Applies impulse to the object.

If Local == TRUE, apply the Force in local coordinates; otherwise, apply the Force in global coordinates.

This function only works on physical objects.

Parameters

Force (vector): Amount of impulse force to apply.
Local (integer): Boolean, if TRUE, force is treated as a local directional vector instead of region directional vector.

Technical Details

Return Type: void
Energy: 10

This function applies an instantaneous impulse to a physical object. The momentum parameter should be expressed in Lindograms × meters per second (not kilogram-meters per second). For continuous force application, use llSetForce instead.

Important Notes

The momentum parameter is applied to the center of mass
Momentum represents mass × velocity needed to achieve an initial velocity when no other forces (gravity, collisions) are present
The magnitude of momentum may be scaled back by the object’s available energy:
- For heavy objects: momentum is capped at 20,000 (not 20)
- For fast objects: velocity is capped at ~202 meters/second, so momentum reflects this velocity cap
The function uses the legacy script “energy budget” system, which can cause unpredictable attenuation if the scripted object doesn’t have enough energy budget
The function has high griefing potential, so it was deliberately hobbled with high energy consumption

Momentum vs. Force vs. Velocity

Momentum: mass × velocity (used here)
Parameter units: Lindograms × m/s (where Lindograms are Second Life’s mass unit)
Use llGetMass() to get object mass in Lindograms
Use llGetMassMKS() to get object mass in Kilograms

Examples

Example 1: Reach Target Velocity Regardless of Mass

//This script will apply an impulse to reach a target velocity value, regardless of object mass.
vector start;
rotation startRot;

float Velocity = 13.0; //meters / second.

default
{
    touch_start(integer total_number)
    {
        llSay(0, "Launching!");
        start = llGetPos();
        startRot = llGetRot();
        llSetStatus(STATUS_PHYSICS, TRUE);     // Make sure prim has physics enabled

        vector adjVelo = <0,0,Velocity>*llGetMass(); //Factor object mass (in Lindograms) into velocity calc. Lg*m/s
        llApplyImpulse(adjVelo, TRUE);
        llSetTimerEvent(0.1);
    }

    land_collision_start(vector start)
    {
        llSetLinkPrimitiveParamsFast(LINK_ROOT,[PRIM_PHYSICS,FALSE,PRIM_POSITION,start,PRIM_ROTATION,startRot]);
        llSetTimerEvent(0);
    }

    timer()
    {
        llOwnerSay((string)llGetVel()); //Report velocity value back to owner.
    }
}

Example 2: Launch Object at Owner

//  Rez an object, and drop this script in it.
//  This will launch it at the owner.

default
{
    state_entry()
    {
        key ownerKey = llGetOwner();
        vector ownerPosition = llList2Vector(llGetObjectDetails(ownerKey, [OBJECT_POS]), 0);

        //  if the owner is not in the sim, stop fooling around
        if (llGetAgentSize(ownerKey) == ZERO_VECTOR)
            return;

        //  else
        llSetStatus(STATUS_PHYSICS, TRUE);

        vector objectPosition = llGetPos();
        vector direction = llVecNorm(ownerPosition - objectPosition);

        llApplyImpulse(direction * llGetMass(), 0);
    }
}

Example 3: Interactive Target Practice (Beer Can)

Make yourself a beer can, drop this script into it, and have some target practice.

vector gHome;
integer gHit;

default
{
    collision_start(integer num)
    {
        if (!gHit)
        {
            llSetTimerEvent(15.0);
            gHome = llGetPos();
            gHit = TRUE;
        }
        llSetStatus(STATUS_PHYSICS, TRUE);
        llTriggerSound("b90ed62a-2737-b911-bb53-6b9228bbc933",1.0);
        llApplyImpulse(llGetMass()*<0,0,5.0>,TRUE);
        llApplyRotationalImpulse(llGetMass()*<llFrand(1.0),llFrand(1.0),llFrand(1.0)>,TRUE);
        llResetTime();
    }

    land_collision(vector where)
    {
        if (llGetTime() < 0.5)
        {
            llResetTime();
            llApplyImpulse(llGetMass()*<0,0,llFrand(1.0)>,TRUE);
            llApplyRotationalImpulse(llGetMass()*<llFrand(1.0),llFrand(1.0),llFrand(1.0)>,TRUE);
        }
    }

    timer()
    {
        llSetStatus(STATUS_PHYSICS,FALSE);
        gHit = FALSE;
        llSetRegionPos(gHome);  // Send the can home, even if more than 10m away
        llSetRot(ZERO_ROTATION);
        llSetTimerEvent(0.0);
    }
}

Example 4: Demonstrating Momentum vs. Velocity Cap

// Demonstrates that:
// - The parameter is momentum, not force
// - Initial velocity * mass = momentum when no other forces act
// - Momentum is capped at 20,000
// - Velocity is capped around 200 m/s (so momentum reflects this)

integer tid;
vector initPos;
vector Impulse;
default
{
    state_entry()
    {
        llSetPhysicsMaterial(GRAVITY_MULTIPLIER,0,0,0,0);
        llSetStatus(STATUS_PHANTOM, TRUE);
        llSetStatus(STATUS_PHYSICS, TRUE);
    }

    touch_end(integer n)
    {
        tid=llTarget(initPos=llGetPos(),30);
        llSetStatus(STATUS_PHYSICS, TRUE);
        Impulse = llGetMass()*<0,0,25>;
        llOwnerSay(llList2Json(JSON_ARRAY, [ "Setup a Momentum=", Impulse  ]));
        llApplyImpulse( Impulse , FALSE);
    }
    moving_start()
    {
        llOwnerSay(llList2Json(JSON_ARRAY, [ "Velocity= ", llGetVel(), "Force=",llGetMass()*llGetAccel(), "Momentum=", llGetVel()*llGetMass()]));
    }
    not_at_target()
    {
        llSetTimerEvent(0.0);
        llTargetRemove(tid);
        llSetStatus(STATUS_PHYSICS, FALSE);
        llSetRegionPos(initPos);
    }
}

// Example output from light object:
//  ["Setup a Momentum=","<0.000000, 0.000000, 183.181381>"]
//  ["Velocity=","<0.000000, 0.000000, 25.000002>","Force=","<0.000000, 0.000000, -0.171902>","Momentum=","<0.000000, 0.000000, 183.181396>"]

// Example output from heavy object (momentum capped at 20000):
//  ["Setup a Momentum=","<0.000000, 0.000000, 28244.332031>"]
//  ["Velocity=","<0.000000, 0.000000, 17.702671>","Force=","<0.000000, 0.000000, -28.363781>","Momentum=","<0.000000, 0.000000, 20000.005859>"]