5.3 Interpolating on Tables with Negative Numbers

Marilyn Nielson

Applications

Objectives

When you’ve finished this chapter, you’ll be comfortable with the arithmetic required to interpolate between values in a table that includes negative or decreasing numbers.

Sometimes we work with tables where values are negative, or where in at least a part of the table, cell values decrease. One example is wind chill tables.

 

A wind chill chart showing effective temperature at a given wind speed and air temperature.
This windchill chart shows the effective temperature on your skin at a given wind speed and temperature. Note that all of the cell values are negative.

We’ll use the same approaches to interpolation when working in tables where values are negative, but we need to pay extra attention to the signs. These examples should help!

Examples

A) Use this table for wind chill to complete the following interpolations.

  • Find the wind chill when the temperature is 15ºF and the wind is 30 mph.
  • Find the wind chill when the temperature is 15ºF and the wind is 32 mph.
  • Find the wind chill when the temperature is 17ºF and the wind is 30 mph.
  • Find the wind chill when the temperature is -20ºF and the wind is 14 mph.

B) Use the humidity table to complete these interpolations.

  • Find the relative humidity when the wet bulb is -6ºC and the dry bulb is 6ºC.
  • Find the relative humidity when the wet bulb is -8ºC and the dry bulb is -7ºC.
  • Find the relative humidity when the wet bulb is 3.5ºC and the dry bulb is 4ºC.
  • Find the relative humidity when the wet bulb is 3.5ºC and the dry bulb is 6.5ºC.

 

 

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