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## Significant Figures and Order of Magnitude | Boundless Physics

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### One Response to “What does an Earthquake’s Magnitude Mean?”

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## A Matter of Magnitude by Al Sevcik

Elle Casey. The Wildside Book of Fantasy. Gene Wolfe. As such, values are expressed in the form of a decimal with infinite digits. The more digits that are used, the more accurate the calculations will be upon completion. Using a slew of digits in multiple calculations, however, is often unfeasible if calculating by hand and can lead to much more human error when keeping track of so many digits.

However, for the convenience of performing calculations by hand, this number is typically rounded even further, to the nearest two decimal places, giving just 3. However, when doing a series of calculations, numbers are rounded off at each subsequent step. This leads to an accumulation of errors, and if profound enough, can misrepresent calculated values and lead to miscalculations and mistakes.

Rounding these numbers off to one decimal place or to the nearest whole number would change the answer to 5.

## What does an Earthquake’s Magnitude Mean?

The more rounding off that is done, the more errors are introduced. An order of magnitude is the class of scale of any amount in which each class contains values of a fixed ratio to the class preceding it.

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In its most common usage, the amount scaled is 10, and the scale is the exponent applied to this amount therefore, to be an order of magnitude greater is to be 10 times, or 10 to the power of 1, greater. The order of magnitude of a physical quantity is its magnitude in powers of ten when the physical quantity is expressed in powers of ten with one digit to the left of the decimal.

Orders of magnitude are generally used to make very approximate comparisons and reflect very large differences. If two numbers differ by one order of magnitude, one is about ten times larger than the other. If they differ by two orders of magnitude, they differ by a factor of about Two numbers of the same order of magnitude have roughly the same scale — the larger value is less than ten times the smaller value. It is important in the field of science that estimates be at least in the right ballpark.

In many situations, it is often sufficient for an estimate to be within an order of magnitude of the value in question. Although making order-of-magnitude estimates seems simple and natural to experienced scientists, it may be completely unfamiliar to the less experienced. Some of the mental steps of estimating in orders of magnitude are illustrated in answering the following example question: Roughly what percentage of the price of a tomato comes from the cost of transporting it in a truck? Guessing the Number of Jelly Beans : Can you guess how many jelly beans are in the jar?

If you try to guess directly, you will almost certainly underestimate. The right way to do it is to estimate the linear dimensions and then estimate the volume indirectly. If the magnitudes are not integers, or you want to do it in fewer steps, you can simply find the difference in magnitudes, and raise the number 2.

For another example, we can figure out how many times brighter the Sun is than the brightest star in the night sky, Sirius. Sirius has an apparent magnitude of Find the difference and raise 2. The original system of magnitudes was developed to measure how bright a star appears to be from Earth, what we now call apparent magnitude. But apparent magnitude is often a poor indicator of how truly bright a star is. The reason is that they are so far away.

Sirius is the brightest star in the sky, but not just because it is hot and luminous; it is also quite close to us. Distance can make a luminous star look dim and a dim star look deceptively bright. So the absolute magnitude of a star is the apparent magnitude it would have if it were at a distance of 10 parsecs from us. Do the stuff in parentheses first:.

Now take the logarithm of 0. Multiply the two negatives to get a positive:. Now take the logarithm of Note the logarithm was positive this time:. Despite the fact that they look almost identically bright to the eye, the two stars have radically different luminosities!