Final answer:
The Song Dynasty introduced paper money to make money lighter. Paper money was easier to carry and use compared to heavy copper coins.
Step-by-step explanation:
The Song Dynasty introduced paper money to make money lighter.
Before the Song Dynasty, most transactions in China were conducted with copper coins, which were heavy and cumbersome. To make money lighter, the Song Dynasty introduced the use of paper money, also known as 'jiaozi', as a form of currency. Paper money was lighter and more convenient to use than copper coins, making it easier for people to carry and conduct transactions.
Examples: People could carry a large amount of paper money in their pockets or wallets, whereas carrying an equivalent amount of copper coins would be extremely heavy and cumbersome.