How to change Velocity when player touches a specific brick?

I am trying to increase the velocity of a block when a player touches/sits on it and then set the velocity to 0 when a player isn't touching it. I am trying to make a swing. I am not quite sure what to do but this is what I have so far:

script.Parent.Touched:connect(function(hit)
    if hit.Parent:FindFirstChild("Humanoid") then
        game.Workspace.SwingSeat1.Velocity = Vector3.new(400,0,0
 )
    end
end)

When I sit on the swing it doesn't move.