Conversion Factor Method

**The conversion factor method** is a powerful problem solving tool that often goes by a variety of names: dimensional analysis, unit-factor method, factor-label method, to name a few. The method is the same regardless of the name. The method is based on quantities that can be defined as equalities.

Therefore, from any equality two fractions can be formed, each equal to one.

In terms of measured quantities:

Multiplication by either of these factors will not change the value of a measurement, but only the unit in which it is expressed.

application:

If it takes 2.5 minutes to complete a task, what is that same length of time in seconds?

Steps in the Conversion Factor Method

- Write down the number and unit given.
- Multiply by a conversion factor so that the units given cancel and the units desired are left.
- Check the units. Cancel.
- Calculate

Example:

If 1 cal = 4.184 J

If a container of water absorbs 3.4 cal of heat, what is the amount of energy absorbed (in joules)?

answer is rounded to two significant figures

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