# PhysObj:ApplyForceCenter

PhysObj:ApplyForceCenter( Vector impulse )

# Description

Applies the specified impulse in the mass center of the physics object.

This will not work on players, use Entity:SetVelocity instead.

# Arguments

1 Vector impulse
The impulse to be applied in `kg*source_unit/s`. (The vector is in world frame)

## Example

An entity that simulates its own gravity by applying a force downward on the entity based on the force equation:

`(Force = mass * acceleration)`

Since, by default, entities already have gravity, the default gravity must be turned off by adding `phys:EnableGravity(false)` in the entity's Initialize function so that the default gravity doesn't interfere with our custom gravity.

NOTE: We can get the mass of the entity by using the PhysObj:GetMass function.

-9.80665 (meters / second ^ 2) Is the approximate acceleration of objects on Earth due to gravity. (It is negative because gravity pushes things downwards.)
Considering that the unit of the impulse that ApplyForceCenter accepts is kg*source_unit / s, we have to do unit conversion: 1 meter ≈ 39.37 source units (on entity scale)
function ENT:Initialize() self:SetModel( "models/hunter/blocks/cube1x1x1.mdl" ) self:PhysicsInit( SOLID_VPHYSICS ) self:SetSolid( SOLID_VPHYSICS ) self:SetMoveType( MOVETYPE_VPHYSICS ) local phys = self:GetPhysicsObject() if phys:IsValid() then phys:EnableGravity( false ) -- This is required. Since we are creating our own gravity. phys:Wake() end end function ENT:PhysicsUpdate( phys ) local force = phys:GetMass() * Vector( 0, 0, -9.80665 ) * 39.37 -- This gives us the force in kg*source_unit/s^2 local dt = engine.TickInterval() -- The time interval over which the force acts on the object (in seconds) phys:ApplyForceCenter( force * dt ) -- Multiplying the two gives us the impulse in kg*source_unit/s end