A wire is hanging from a dark high tower so that its upper end is not visible. how can the length of the wire be determined?
The length of the wire can be determined in a following way. If the starting point of the wire is from the top of the tower then the height of the tower is equal to the length of the wire. So, if we know the height of a tower, the length of a wire is determined automatically. Another way to do that is to drop down the wire from the tower and measure its length in a standard way. Also we can bind a weight to the free end of the wire and measure its elongation. Then, if the coefficient of elongation of the wire is known, we can determine the length of the wire.