LSL Wiki Mirror : llApplyImpulse

llApplyImpulse(vector force, integer local)

If an object is physical, this call applies a single push in a specific direction to the object defined by the argument force. If local is true, force is applied along the object's local axis, otherwise it is applied along the global axis.

Note: unlike llApplyRotationalImpulse, llApplyImpulse does work on attachments.

To set the object's velocity using llApplyImpulse():

setVel(vector newVel, integer localAxis)
{
     vector curVel = llGetVel();
     
     if(localAxis)
     {
          rotation rot = llGetRot();
          curVel /= rot; // Un-rotate curVel.
     }

     newVel -= curVel;
     newVel *= llGetMass();

     llApplyImpulse(newVel,localAxis);
}

Compare with llApplyRotationalImpulse.

In order to give an object a specific speed and direction, use the momentum equation: p=m*v where v is the target velocity vector and m is the mass of the object.

llApplyImpulse(llGetMass()*<0,0,10>,FALSE);
//10 meters per second upwards
//Gravity will slow the object down immediately and make it fall back

To overcome gravity effects, use a force which, unlike an impulse, is constant over time:

llSetForce(<0,0,9.8>*llGetMass(),FALSE);
// will cancel the effects of gravity

To stop a moving object dead in its tracks, apply an impulse to counter its current impulse:

llApplyImpulse(-llGetMass()*llGetVel(),FALSE);
//This will cancel the speed of an object that has no other forces set on it
//and will cause it to stop in place relative to the ground

Limitations

The actual impulse may be less than requested for two reasons.

The push vector magnitude is limited to 20,000. Anything over this is scaled back to a magnitude of 20,000.
The push vector is always scaled by the energy of the object. For relatively small objects (say, smaller than an avatar), the object's energy is likely to be 1.0, in which case there will be no effect. However, for large objects, or objects that are being manipulated a lot, the energy may be anywhere from 0.0 to 1.0, and the effect can be very sizeable. See energy for more details on how energy is calculated.

Functions | Dynamics | Force | Impulse