A
stock's price movement, up and
down until the end of the
trading day, is strictly a
result of supply and demand. The
SUPPLY is the number of shares
offered for sale at anyone one
moment. The DEMAND is the number
of shares investors wish to buy
at exactly that same time.
As you can see, what a share
of a company is worth on anyone
day, or at any one minute, is
determined by all investors
voting with their money. If
investors want a stock and are
willing to pay more, the
price will go up. If
investors are selling a stock
and there aren't enough buyers,
the price will go down.
Period.