Maths help needed please

[RogerS]

I'm trying to work out the angle of a slope that drops 18mm per metre. I keep getting about 1 degree which seems very small. Any mathematical brains out there that can check if I'm right, please?

Thanks

 

[RogerM]

Roger - the "1 in 60 rule" says that a 1cm drop in 60cms is 1 degree.

100cm/60cm x 1 cm = 1.67 cms ( or 16.7 mm), so a fall of 18 mm in 1 meter is going to be just over 1 degree - i.e. about 1.08 degrees.

Of course if you want a REAL mathematical calc you'll need to ask someone with a keener brain than mine - but I think you'll find this is as close as a woodworker will need! :lol:

 

[jasonB]

The Tan of the angle will be the opposite over the adjacent.

Tan x = 18/1000

Tan x = 0.018

x = 1.0312 degrees

Jason

 

[paulm]

Working on the basis that for 45 degrees you have a fall of 1 in 1, then I think a fall of 18 in 1000 that you are looking for would be 45 x (18/1000) which is 0.81 degrees which is about what you figured.

Not certain of the above though, it's been a long day !

You do mean 18mm and not cm presumably ?

Cheers, Paul.

 

[Anonymous]

The Tan of the angle will be the opposite over the adjacent.

Tan x = 18/1000

Tan x = 0.018

x = 1.0312 degrees

Jason

This is the one

 

[RogerM]

The Tan of the angle will be the opposite over the adjacent.

Tan x = 18/1000

Tan x = 0.018

x = 1.0312 degrees

Jason

There you are Roger - a real mathematical answer! :lol: My rule of thumb got within 1/20th of a degree so it aint all that bad.

Paul - you are using similar logic to the "1 in 60 rule" which is good up to about 10 degrees. i.e. a fall of 10cms in 60 cms gives an angle of about 10 degrees. Beyond that the rule starts to lose some of its accuracy and 45 degrees is quite a few too far!

Another useful rule of thumb is the "Rule of 72". This states that if you divide a rate of interest into 72, the resulting number is the number of years for your capital to double if that interest is compounded.

So, for example, if you apply 6% to your capital (reinvesting the interest) then it will take 12 years to double your money. Try applying 6% to £100 for 12 years. Your calculator will show a final answer of £201.22 - so it's a pretty good approximation - huh?!

Alternatively, using the same rule, with inflation of 3% it will take 24 years for your capital to halve in its buying power. The actual answer is a smidgeon (this is a technical term) under 23 years, so the rule works pretty well.

OK - sorry - but I find this stuff interesting anyway. I'm a sad man, I know. I'll get me coat!

 

[jasonB]

but I think you'll find this is as close as a woodworker will need! :lol:

I think you will find Roger S is playing with pipework not wood

Bit too shallow an angle for my liking, make sure you put a rodding point at the end of the run :wink:

Jason

 

[RogerS]

Thanks everyone for the reassurance and tips.

JasonB is, as usual, bang on as it is a soil pipe and I agree....one degree is a bit shallow.

-2 degrees outside today. Boy..am I really enjoying this.

 

[titan]

but I think you'll find this is as close as a woodworker will need! :lol:

I think you will find Roger S is playing with pipework not wood

Bit too shallow an angle for my liking, make sure you put a rodding point at the end of the run :wink:

Jason

18mm fall per metre run is the minimum allowed , all the details are in the building regs which are free to download here.

Ian


www.planningportal.gov.uk/england/profe ... 10382.html

 

[devonwoody]

RogerM, I wish I had known those financial formulae years ago, it would have got me off to sleep much earlier than counting it on my fingers.

quote

Another useful rule of thumb is the "Rule of 72". This states that if you divide a rate of interest into 72, the resulting number is the number of years for your capital to double if that interest is compounded.

So, for example, if you apply 6% to your capital (reinvesting the interest) then it will take 12 years to double your money. Try applying 6% to £100 for 12 years. Your calculator will show a final answer of £201.22 - so it's a pretty good approximation - huh?!

Alternatively, using the same rule, with inflation of 3% it will take 24 years for your capital to halve in its buying power. The actual answer is a smidgeon (this is a technical term) under 23 years, so the rule works pretty well.

OK - sorry - but I find this stuff interesting anyway. I'm a sad man, I know. I'll get me coat!