heights along a slope or baseline

delboy2071

Board Regular
Joined
Jun 13, 2005
Messages
75
Hi to all,
seem to be having a mad half hour and cannot seem to find what i think is a simple trig error (some-where).
will keep it short a to the point.

have a baseline of 100m long, a change in height of 10m from one end to the other.
have calculated both slope ratio and slope % with no bother e.g slope % is = 10%

now keeping in mind that when i travel along this baseline, for every 10m travelled i should rise/fall 1m so by the 100th metre i am now 10m higher or lower than from the start.

Sound easy!!!!
using base length*TAN(slope%) the answer am getting is 1.003m not 1.000m
can anyone help

 

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SteveO59L

Well-known Member
Joined
Apr 21, 2004
Messages
7,896
Tangent = opposite/Adjacent

=10 / 100

=0.1

Therefore, for a horizontal distance of 10m, the vertical distance would be

0.1 * 10 = 1m
 

Oaktree

MrExcel MVP
Joined
Jun 20, 2002
Messages
8,010
Office Version
  1. 365
Also note that your slope % is not the same as the angle. If your height is 10 and your length is 100, your angle is about 5.71 degrees (0.099669 radians).

If opposite/adjacent is small, opposite/adjacent can be a good approximation for the angle itself (consider the case of 0.1%); but, as opposite/adjacent gets larger, this approximation gets worse.

So, your tan(slope %) = 0.100335 is a pretty close approximation to tan(0.99669) = 0.1 , but it's not the same.
 

delboy2071

Board Regular
Joined
Jun 13, 2005
Messages
75
Steve,
thanks for that, seems obvious now.

was using the Tan function twice without noticing.

once again

Cheers
 

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