- RATES OF CHANGE:
A rate of change is always a fraction. The numerator is a difference between two values,
a later value minus an earlier value.
The denominator of a rate fraction is always a measurement of time in seconds, minutes, or other time units.
IMPORTANT: The rate is always expressed as a positive number if the numerator is increasing,
with the later value greater than the earlier one.
The rate is considered negative if the later value is less than the earlier value and the difference in the numerator is negative.
The formula for any rate of change is:
| Rate = | _ Final value - Initial value _
Elapsed time
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The units of any rate of change are always numerator units divided by time units.
- SAMPLE PROBLEM:
If a cup of tea cools from 50o C to 35o C in 18 minutes, what is the rate of change?
Answer:
_ 35o C - 50o C _
18 min
| = -15o C / 18 min = -0.83 oC /min
|
(to two significant figs. because all given quantities were expressed to 2 sig. figs.)
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