Ken Herington wrote:
This might sound like a really easy question for you guys but I am new to using numbers. When I select a cell to enter a formula and refer to a cell eg C2, and multiply it by another cell (D2), i keep getting an error message which says " the operator "*" expects a number, but cell 'Mass (kg)' Jupiter contains a string". It is like it thinks I am referring to the cells which have the titles in them, Mass (kg) is cell C1 and D1 is what says Jupiter but i want it to multiply the numbers that are in cells C2 and D2.
Does anyone have any ideas?
Hi Ken,
Two. One on the formula, and one on the unit you've used.
Formula:
=C2*D2 Placed in any cell (except C2 or D2) will return the product of the numbers in C2 and D2, provided both cells either contain numbers or are empty.
=C*D Placed in any cell
in row 2 (except C2 or D2) will return the product of the numbers in C2 and D2, provided both cells either contain numbers or are empty.
=C*D$2 Placed in any cell
in row n (except Cn or D2) will return the product of the numbers in Cn and D2, provided both cells either contain numbers or are empty. This would allow you to make Row 2 a header row, place the 'Jupiter factor' in D2, list the 'Mass (kg)' (see comment below) starting in row 3, and calculate the product in column D, starting at row 3.
The error message may, as Yvan notes, result from the formula referring to cell C1, where it finds the text string 'Mass (kg)', or, if the formula is not referencing C1, the cell which it is referencing may include text (eg. '100 kg' instead of '100'), or may have been formatted as text. Inclusion of any non-numeric characters (with a few exceptions) in the cell will cause the contents to be interpreted as a text string. Formatting a cell as text will cause anything in that cell (including a number or a formula) to be interpreted as a text string.
Units:
The mass of an object is an intrinsic property of that object, and does not change as the object is transferred from planet to planet. A 1 kg object has a mass of 1 kg whether it is on Earth, the moon, Jupiter or en route from one to another of these bodies. Measuring the object's mass using an equal arm balance or a counterpoise balance will give the same reading (1 kg) in each location (although mechanical considerations may limit the precision of that measurement).
The weight of an object, on the other hand, is a measure of the vertical
force exerted on the object due to the gravitational attraction of another object. That weight depends on the mass of the object itself, the mass of the 'other' object(s), and the distance separating the pair. That 1 kg object above will have a different weight on each of the planets, and will vary by about 0.5 percent when determined at different locations on Earth (heaviest at the poles, lightest atop a high mountain at or near the equator). Weight can be measured using a spring scale, which measures the force necessary to support an object against the local gravitational force on that object.
The proper unit of weight in the International System of Units is the Newton, but in common and commercial use (on earth) when we 'weigh' something, we're actually determining its mass, so using the mass unit to report the result is appropriate. Here, though, my interpretation is that you want to determine the 'weight' of the object, not its 'mass', and you should make that distinction in your labels.
Regards,
Barry
