Why do stock market rates rise and fall within minutes and hours?

[B3n car0l]

As far as I'm concerned with, the stock market is a place where second-hand shares are sold and bought. So how can it rise and fall within a minute or hour?
Can you please clarify me what stock market rate means?

[Judy]

Day traders and hedge funds.
They are playing earnings and indexes such as consumer price index.
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[La]

Because their value fluctuates depending the price it is bought and sold at, what others value it at, and its demand.

[bhanwar b]

in fact this is a speculators market.
all speculators trade for their greed and are afraid of loosing.
all usually change their strategy as per mauplated demand and supply in market frequently causing volatile rates.

[James Kimani]

the market fluctuations are dependent on emotions and the laws of supply and deman. Let me illustrate; a stock like for facebook is floated and because many people like the site and know how big it is, the stock's price rises to sky high levels even if the company itself is a poorly run business. The fact that all the available shares have been snapped up creates a shortage meaning that prices can only go higher. After a week, people start neglecting or ignoring the facebook fad and the prices start falling again. Following this fluctuations is what is called speculation and is is an unhealthy way to invest because you are putting your money on human emotion. Other emotions that control market fluctuations are greed and fear; two other emotions that are very hard to control. Hope this helps