How to apply a force to a part?

[CheezeNibletz (Cheezey)]

I want to eject bullet casings from when a gun is fired, how do I apply a sideways force to the bullet casing so that it looks like its being ejected out of the gun?

[ThanksRoBama (Emma)]

You can apply an impulse to it or just set the AssemblyLinearVelocity. If you’re using a Part welded to the weapon model to indicate the relative CFrame of the ejection port, something like this should work:

local SHELL_CASING_EJECTION_SPEED = 50

local shellCasingPrefab = game.ReplicatedStorage -- ...fill in
local ejectionPort = gunModel.EjectionPort

function ejectShellCasing()
    local shellCasing = shellCasingPrefab:Clone()
    shellCasing:PivotTo(ejectionPort.CFrame)
    shellCasing:ApplyImpulse(ejectionPort.CFrame.RightVector * SHELL_CASING_EJECTION_SPEED)
end