After a number of weeks in which the Dow Jones Industrial Average (^DJI -0.12%) rose or fell more than 100 points multiple days in a row, this week has been very calm -- the largest move the index made over the past four trading sessions was on Tuesday when it rose 88 points. Furthermore, despite declining two of the past four days, the Dow looks as if it will end the week higher even if the 19 points the blue-chip stocks are down as of 12:45 p.m. EDT holds for the remainder of the day. But based on what the other two major indexes are doing today, that may not be the case. Although it has been an up-and-down day for the S&P 500, the index is currently just 0.01% lower, while the NASDAQ is easily higher by 0.34%.

Let's briefly take a look at a few of the reasons why the Dow is lower today.

Shares of both the Dow's oil companies, Chevron (CVX 0.08%) and ExxonMobil (XOM -0.05%), are trading lower today as the price of light crude oil falls 2.74%. Chevron is currently down 1.02% as Exxon has declined 1.23%. Both companies are highly dependent on the price of oil, and when the value of black gold declines, the profits for the major oil companies falls right alongside. Long-time shareholders of either company know that these stocks are rather volatile and move up and down more than 1% regularly, but investors who are just considering these stocks need to determine if they can handle the roller-coaster ride before they strap into the seat.  

Another Dow component losing today because of falling commodity prices is Caterpillar (CAT -0.43%); shares are down 2.11%. While Caterpillar does not have any direct relationship with commodities, a large portion of the company's business is selling heavy machinery to companies that mine for different commoditized metals. With the price of gold way off its highs of just under $1,800 per once, and down another 3% today, the gold miners will likely begin cutting back on expenses, which may include new equipment. Additionally, both silver and platinum are lower by more than 2.5% today and have also followed the downward slope that gold has been riding the past few weeks.  

As the metals markets decline across the board today, the aluminum giant Alcoa (AA) is also down 1.71%. This is bad news to some, but great news to other investors who have a short interest in the stock, which is currently a rather large number of people. Currently, Alcoa is the second most shorted Dow component, and it seems that the number of shares that have been shorted has continued to grow over the past few months. While average-joe investors may see shorting as an easy way to make money, like with the oil companies, they need to fully understand the risks involved with this type of investing before getting starting.