-The weight of an object cannot be represented by a negative number since it represents the mass of an object and by definition, mass cannot be negative.
-The ocean depth is measured with respect to the sea level. The sea level is considered the point of elevation/depth zero. Any distance below sea level (depth) can be expressed as a negative number, so the ocean depth of 100feet can be expressed as an "elevation of -100ft", the negative number indicates that the measure is below sea level.
-Temperatures can be expressed as negative numbers if they are below 0ºC (cold temperatures)
-The elevation above sea level indicates that it is above 0ft, by definition any number greater than zero is positive so an elevation of 30ft cannot be expressed as a negative number.
-A debt of $60
If you make a balance of debts and earnings, a balance of $0 indicates that there are no debts and there are no earnings.
A balance above $0, indicates that there are earnings, for example, +$60 would represent that you earned sixty dollars.
A balance below $0, indicates that there is a debt, so a balance of "-$60" would indicate that you owe sixty dollars.
-Angles can be expressed as positive or negative values depending on their direction with respect to a point. If the angle rotates in a counter-clockwise direction, it can be expressed as a positive value, for example, 90º
If the angle rotates in a clockwise direction can be expressed as a negative angle, for example, -90º
The situations that can be expressed by a negative number are the ocean depth, the temperature, the debt and the angles