Why does customphysicalproperties not work?

I'm using the command bar in roblox studio to change the customphysicalproperties of multiple parts at once with the same name. Why does this not work?

density = 10
friction = 0
elasticity = 0
frictionWeight = 0
elasticityWeight = 0

physProperties = PhysicalProperties.new(density, friction, elasticity, frictionWeight, elasticityWeight)


 for i, v in pairs(workspace:GetChildren()) do
    if v.Name == "Tie" then 
    v.CustomPhysicalProperties = physProperties end
end