Understanding Vending Machines

Vending machine
A vending machine is a machine that provides various snacks, beverages and other products to consumers. The idea is to vend products without a cashier. Items sold via vending machines vary by country and region.
In many countries, vending machines generally serve the purpose of selling snacks and beverages, but are also common in busy locations to sell other items such as newspapers.
Some countries sell alcoholic beverages such as beer through vending machines, while other countries do not allow this (usually because of dram shop laws).
A number vending machine is also used at many outlets, where a customer has to press a button on the machine and a number is printed on a slip of paper and the customer has to wait until his number is called by the service provider.
Cigarettes were commonly sold in the United States through these machines, but this practice is increasingly rare due to concerns about underaged buyers. Sometimes a pass has to be inserted in the machine to prove one's age. In some countries like Germany and Japan, by contrast, cigarette machines are still common. Vending machines were used at airports from the 1950s well into the 1970s to sell life insurance policies covering death in the event that the buyer's flight crashed. Such policies were quite profitable, because the risk of any given flight crashing was (and remains) very low, but this practice gradually disappeared due to the tendency of American courts to strictly construe such policies against their sellers, such as Mutual of Omaha
History
The first recorded reference to a vending machine is found in the work of Hero of Alexandria, a first-century engineer and mathematician. His machine accepted a coin and then dispensed a fixed amount of holy water.[2][3] When the coin was deposited, it fell upon a pan attached to a lever. The lever opened up a valve which let some water flow out. The pan continued to tilt with the weight of the coin until it fell off, at which point a counter-weight would snap the lever back up and turn off the valve.
Despite this early precedent, vending machines had to wait for the Industrial Age before they came to prominence. The first modern coin-operated vending machines were introduced in London, England in the early 1880s, dispensing post cards. The first vending machine in the U.S. was built in 1888 by the Thomas Adams Gum Company, selling gum on train platforms. The idea of adding simple games to these machines as a further incentive to buy came in 1897 when the Pulver Manufacturing Company added small figures which would move around whenever somebody bought some gum from their machines. This simple idea spawned a whole new type of mechanical device known as the "trade stimulators". The birth of slot machines and pinball is ultimately rooted in these early devices.
Mechanism
After paying, a product may become available by:
the machine releasing it, so that it falls in an open compartment at the bottom, or into a cup, either released first, or put in by the customer
the unlocking of a door, drawer, turning of a knob, etc.
Sometimes the product is not just released, but prepared; this may be the case e.g. in the case of coffee, french fries, or a ticket that is printed after paying.
The main example of a vending machine giving access to all merchandise after paying for one item is a newspaper vending machine (also called vending box). It contains a pile of identical newspapers. After a sale the door automatically returns to a locked position. A customer could open the box and take all of the newspapers or, for the benefit of other customers, leave all of the newspapers outside of the box, slowly return the door to an unlatched position, or block the door from fully closing, each of which are frequently discouraged, sometimes by a security clamp. The success of such machines is predicated on the assumption that the customer will be honest (hence the nickname "honor box"), which is helped by the fact that having more than one newspaper is not often useful.