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Aggregate demand and aggregate supply

When a company makes plans for how much to produce and what prices to set, it needs information. The company needs to predict the level of supply that will be required to meet demand. It needs to set prices that will keep the business running. In the same way, governments need this information for the whole economy. The total level of demand for all products and services is called the aggregate demand. The total supply is called the aggregate supply.

The demand for products and services is how much is wanted. For a company, the demand comes from customers. For a whole economy, things are a little more complicated. Demand in the whole economy comes from the following:

- from consumers, because they buy products and services (consumption)

- from companies, because they invest money to build factories and buy machines (investment)

- from the government, because they spend money on services and projects (government spending)

- from exports, because these are sales to customers in other countries (export)

Although aggregate demand is made up of many things, it behaves in the same way as demand for a single product. For example, demand rises when incomes rise. The same applies to aggregate demand. Similarly, demand falls as prices rise. The same is true for aggregate demand. You can see this relationship shown in figure 1 on page 63. The vertical axis shows prices. The horizontal axis shows real national income. Real national income is the value of all the services and products produced by the whole economy. It's calculated in the same way as aggregate demand (consumption, investment, government spending and exports). You can sec from the curve that national income (and therefore aggregate demand) increases as prices fall.

Changes in any of the four things which make up aggregate demand will cause a shift in demand. For example, if the government decides to spend a huge amount of money on building new hospitals and schools, this will have an effect on the whole economy. Aggregate demand will increase at all price levels. This is shown in aggregate demand curve 2 (AD2) in figure 1.

The supply curve for an individual product or service is very simple. As the company increases its supply to the market, it increases the price. But what about aggregate supply for the whole economy? This is more complex. In the short run, aggregate supply follows the same trend as the supply for a single product. Supply rises as prices rise. However, the long run is different. In the long run, supply is not affected by price. In the long run, production is limited by the factors of production. In other words, what a country can supply depends on the number of factories it has, the number of people working and the availability of raw materials. This is why the long run supply curve in figure 2 on page 63 is a straight line.



The cash we use every day is something we take for granted, but for thousands of years people traded without it. Before money was invented, people used a system called bartering. Bartering is simply swapping one good for another. Imagine that you have milk, for example, and you want eggs. You simply find someone who has eggs and wants milk - and you swap! However, you can see that this isn't a very convenient way to trade.

First of all, you can't be sure that anyone will want what you've got to offer. You have to hope that you'll be lucky and find someone who has what you want and that he or she wants what you've got. The second problem with bartering is that many goods don't hold their value. For example, you can't keep your milk for a few months and then barter it. Nobody will want it!

After some time, people realised that some goods held their value and were easy to carry around and to trade with. Examples were metals like copper, bronze and gold and other useful goods like salt. These are examples of commodity money.

With commodity money, the thing used for buying goods has inherent value. For example, gold has inherent value because it is rare, beautiful and useful. Salt has inherent value because it makes food tasty. If you could buy things with a bag of salt, it meant you could keep a store of salt and buy things anytime you needed them. In other words, commodity money can store value.

Using commodity money was much more convenient than ordinary bartering, but it still had drawbacks. One of these drawbacks is that commodity money often lacks liquidity. Liquidity refers to how easily money can circulate. There is obviously a limit to how much salt you can carry around! There's another problem with commodity money: not everyone may agree on the value of the commodity which is used as money. If you live by the sea, salt may not be so valuable to you. Money needs to be a good unit of account. In other words, everyone should know and agree on the value of a unit. This way, money can be used to measure the value of other things.

The solution is to create a kind of money that does not have any real intrinsic value, but that represents value. This is called fiat money. The coins and notes that we use today are an example of fiat money. Notes don't have any inherent value - they are just paper. However, everyone agrees that they are worth something. More importantly, their value is guaranteed by the government. This is the reason why pounds and dollars and the world's other currencies have value.


If you work, you've probably got a bank account. You could keep the money you earn each month in a box under your bed, but it wouldn't be very sensible. One reason is that it's not very safe. If your house gets burgled, you'll lose everything you've saved. Another reason is that your money will lose value.

As prices rise, the money in a box under your bed will be able to buy fewer and fewer things. Money in a bank savings account, however, will earn interest. The interest will help compensate for the effect of inflation. But banks are more than just safe places for your money. What other services do they offer?

The other main service is lending money. Individuals and businesses often need to borrow money, and they need a lender that they can trust. This is exactly what banks are - reliable lenders. In fact, most of the money that people deposit in their bank accounts is immediately lent out to someone else.

Apart from storing and lending money, banks offer other financial services. Most of these are ways of making money more accessible to customers. For example, banks help people transfer money securely. They give customers cheque books and credit cards to use instead of cash. They provide ATM machines so that people can get cash any time of the day or night.

But how do banks make a living? Basically, they make a living by charging interest on loans. Of course, when you make a deposit into a bank savings account, the bank pays you interest on that money. However, the rate they pay savers is less than the rate they charge borrowers. The extra money they make by charging interest on loans is where banks earn most of their money.

For banks, interest is also a kind of security. Sometimes people do not pay back money they borrow. This is called defaulting on a loan. When someone defaults on a loan, the bank uses money earned from interest to cover the loss.

All of this means that most of the money people have saved in the bank is not there at all! A small amount of the total savings is kept by the bank so that customers can make withdrawals. The rest, however, is made available for loans. The amount that is kept is called the reserve. The reserve must be a certain percentage of all the savings received from customers - for example 20 per cent. This figure is set by the central bank, and this is one of the ways that governments can control the amount of money circulating in the economy.


Date: 2015-12-24; view: 1754

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