This script should be working, but it's not?

Basically, I want the player to have a particle effect that grows the faster they're moving. The problem is that the rate is always 0. It won't change.

local color1 = Color3.new(1, 1, 1)
local color2 = Color3.new(.3, .3, .3)
local sequence = ColorSequence.new(color1,color2)

local plr = game.Players.LocalPlayer

local p = Instance.new("ParticleEmitter", plr.Character.Torso)
p.Color = sequence
p.Size = NumberSequence.new(2)
p.Transparency = NumberSequence.new(.5)
p.Speed = NumberRange.new(0)
p.Rate = NumberSequence.new(100)
p.Lifetime = NumberRange.new(.1)
p.Texture = "http://www.roblox.com/asset/?id=196969716"

em = plr.Character.Torso.ParticleEmitter

while true do
    wait(0.1)
    p.Rate = NumberSequence.new(100)
    run = plr.Character.Torso.Velocity.magnitude * 0.05
    em.Size = NumberSequence.new(run)
end