local phys = {
    tau = 2 * math.pi
}

-- returns true if the two actors intersect
function phys.intersects(actor1, actor2)
    return (actor1.x - actor2.x) ^ 2 + (actor1.y - actor2.y) ^ 2 <= (actor1.radius + actor2.radius) ^ 2
end

-- updates the actor's location by applying the passage of time
-- TODO spin
function phys.update(actor, dt)
    local dv = actor.speed * dt
    actor.x = actor.x + math.cos(actor.angle) * dv
    actor.y = actor.y + math.sin(actor.angle) * dv
end

return phys