The only difference between these two types of moving average is the sensitivity each one shows to changes in the data used in its calculation.
More specifically, the exponential moving average (EMA) gives a higher weighting to recent prices than the simple moving average (SMA) does, while the SMA assigns equal weighting to all values. The two averages are similar because they are interpreted in the same manner and are both commonly used by technical traders to smooth out price fluctuations.
The SMA is the most common type of average used by technical analysts and it is calculated by dividing the sum of a set of prices by the total number of prices found in the series. For example, a sevenperiod moving average can be calculated by adding the following seven prices together and then dividing the result by seven (the result is also known as an arithmetic mean average).
Example Given the following series of prices: $10, $11, $12, $16, $17, $19, $20 The SMA calculation would look like this: $10+$11+$12+$16+$17+$19+$20 = $105 7period SMA = $105/7 = 15 
Since EMAs place a higher weighting on recent data than on older data, they are more reactive to the latest price changes than SMAs are, which makes the results from EMAs more timely and explains why the EMA is the preferred average among many traders. As you can see from the chart below, traders with a shortterm perspective may not care about which average is used, since the difference between the two averages is usually a matter of mere cents. On the other hand, traders with a longerterm perspective should give more consideration to the average they use because the values can vary by a few dollars, which is enough of a price difference to ultimately prove influential on realized returns  especially when you are trading a large quantity of stock.
As with all technical indicators, there is no one type of average that a trader can use to guarantee success, but by using trial and error you can undoubtedly improve your comfort level with all types of indicators and, as a result, increase your odds of making wise trading decisions.
To learn more about moving averages, see Basics Of Moving Averages and Basics Of Weighted Moving Averages.

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Simple Moving Average  SMA
A simple, or arithmetic, moving average that is calculated by ... 
Exponential Moving Average  EMA
A type of moving average that is similar to a simple moving average, ... 
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1. A representative measure of a range of prices that is calculated ...