What's that mean each code :     struct Physics {
        static let smallCoin : UInt32 = 0x1 << 1
        static let smallCoin2 : UInt32 = 0x1 << 2
        static let ground : UInt32 = 0x1 << 3
    }

What that mean

UInt32 = 0x1 << 1 ?

and static let ?