Multiplying two negative numbers together: a real world example?

Rachmaninov · 17 Apr 2012 at 06:03

Good thread because it just made me realize you can't have "minus" objects in reality. I'd never actually thought about it.

D.P. · 17 Apr 2012 at 06:08

Angilion said:
Essentially because people agreed to standardise on base 10. It might be related to almost all people having 10 digits, but there were a fair few cultures that used a different base. My guess is that it came down to dominant cultures using base 10.

Which is a shame. Ase 12 is much nicer giving more factors, 12 is divisible by 6, 4,3 and 2, but 10 only by 5 and 2 (ignoring 1). Thus knowing what half. Foot, a third of a foot, three quarters of fooot s all nice and easy and are not fractions.

Raymond Lin · 17 Apr 2012 at 07:10

D.P. said:
Which is a shame. Ase 12 is much nicer giving more factors, 12 is divisible by 6, 4,3 and 2, but 10 only by 5 and 2 (ignoring 1). Thus knowing what half. Foot, a third of a foot, three quarters of fooot s all nice and easy and are not fractions.

But how about this...(off my head I think this is correct)

1 cubic meter of water weigh 1 tonne at 1 atmospheric pressure.

What is that in the imperial system?

moogle · 17 Apr 2012 at 07:12

Raymond Lin said:
But how about this...(off my head I think this is correct)

1 cubic meter of water weigh 1 tonne at 1 atmospheric pressure.

What is that in the imperial system?

I got an image for that

RomanNose · 17 Apr 2012 at 07:16

Why anyone would want to use imperial is beyond me.

Admiral Huddy · 17 Apr 2012 at 08:19

desires said:
Yup, debt works, that's a good enough real world example for me. Thanks.

Can anyone trump a financial example?

What do you mean by real world example?

We use it for reversing transactions in the banking system to switch the sign from either a DR or CR.

I was always under the impression then when you look at negative and positive figures that you think of a horizontal axis?

Greebo · 17 Apr 2012 at 08:37

RomanNose said:
Why anyone would want to use imperial is beyond me.

You have to remember it's origins and it was logical and could be well approximated without the need for tape measures etc

hand = 4 inches - average man's hand

foot = 12 inches - average man's foot length

yard = 3 foot - average man's stride

chain = 66 feet - was an actual metal chain developed to survey land in 1620

furlong = 10 chains (see below) or 40 rods (length of a medieval ox-goad

Acre = An acre is an area that is one furlong long and one chain wide - came about because of ploughing with horses and is what one team could plough in a day

Mile = 8 furlongs or 100 chains or 320 rods

leicrao1 · 17 Apr 2012 at 08:48

Reminds me of the story of the internationally renowned linguistics professor who gives a public lecture in Glasgow. He makes the point that although there are dozens of languages in the world where a double negative means a positive, he had yet to encounter a single example of a language where a double positive implied a negative. At this point a man at the back shouts out: '...yeah,...right!...'

Srengam · 17 Apr 2012 at 18:19

RomanNose said:
Why anyone would want to use imperial is beyond me.

Because 10 only has two integer factors, 5 and 2 (excluding 1 and 10).

But 12 has 6, 4, 3 and 2, so is twice as convenient.

If I recall right it was the babylonians who introduced it, they had 360 days in a year, which was split into twelve months of 30 days, a circle has 360 degrees, radians are still used and split into /2 /3 /4 /6 etc.

(note, all from memory so could be some mistakes here).

Zefan · 17 Apr 2012 at 18:25

yhack said:
My favourite part was when desires didn't even know it was window.

RomanNose · 17 Apr 2012 at 18:28

Well it used to be convenient not anymore. We are more interested in measuring big numbers and small numbers instead of representing normal integers.
Imperial is absolutely useless at that, radians are a metric unit by the way. Degrees shouldn't be taught imo.

bhavv · 17 Apr 2012 at 18:33

desires said:
I can't think of any real world examples where this can make sense. Now I'm thinking perhaps something at the cellular level and bacteria. I've no idea.

If I dont have 5 apples in one hand, and dont have 5 apples in the other hand, and dont have 5 apples in my fruit basket, and dont have 5 apples in my fridge, and dont have 5 apples in the cupboard ....

Then that means that I have 25 apples. Wait, what?

Or even simpler, it doesnt have to be -5 x -5, it could be -5 x -2 ....

If I dont have 5 apples in one hand, and dont have 5 apples in the other hand, then I have 10 apples.

Maths sure is broken.

Soundood · 17 Apr 2012 at 18:39

-1*-1 + Alt+F4=0

try it on your keyboard and you get the answer

yer_averagejoe · 17 Apr 2012 at 18:40

Srengam said:
Because 10 only has two integer factors, 5 and 2 (excluding 1 and 10).

But 12 has 6, 4, 3 and 2, so is twice as convenient.

If I recall right it was the babylonians who introduced it, they had 360 days in a year, which was split into twelve months of 30 days, a circle has 360 degrees, radians are still used and split into /2 /3 /4 /6 etc.

(note, all from memory so could be some mistakes here).

Not sure you're right about the calendar but the 360 degrees to a circle and our modern clock came from Babylonian base 60 mathematics

TGV · 17 Apr 2012 at 18:42

Imperial dimensions are often used in threaded fasteners even when a rough metric equivalent is available. I used to design IndyCar engine installations and we always used UNF thread forms instead of the equivalent metric form as they performed better in terms of tensile capability to weight ratio.

In terms of negative number multiplication - you come across it in electronics - negative voltages in terms of in relation to ground, and also in AC theory (also complex numbers come into play there).

bhavv · 17 Apr 2012 at 18:42

Also ....

A)

i) 5 x 2 = 10

ii) 5 + 5 = 10

B)

i) -5 x -2 = +10.

ii) -5 + -5 = -10.

I dont comprehend why.

Srengam · 17 Apr 2012 at 18:42

yer_averagejoe said:
Not sure you're right about the calendar but the 360 degrees to a circle and our modern clock came from Babylonian base 60 mathematics

I think it was the romans who introduced the other 5 days once the seasons started displacing. They named the months with extra days after roman leaders, and February has less days cos they needed to take a 6th for Julius Ceaser cos he was awesome but their were no more days available.

Srengam · 17 Apr 2012 at 18:46

bhavv said:
If I dont have 5 apples in one hand, and dont have 5 apples in the other hand, and dont have 5 apples in my fruit basket, and dont have 5 apples in my fridge, and dont have 5 apples in the cupboard ....

Then that means that I have 25 apples. Wait, what?

Or even simpler, it doesnt have to be -5 x -5, it could be -5 x -2 ....

If I dont have 5 apples in one hand, and dont have 5 apples in the other hand, then I have 10 apples.

Maths sure is broken.

How many apples don't you have? . . . (-5)(-5) = 25, you dont have 25 apples.

TheCenturion · 17 Apr 2012 at 18:50

desires said:
I was just thinking about this, I'm pretty good at maths but I'm stumped with this one. If you multiply a negative number by another negative number you get a positive number. I can't think of any real world examples where this can make sense. Now I'm thinking perhaps something at the cellular level and bacteria. I've no idea.

I can think of a real world example

Area is height x width.

If you're plotting something on a graph, and want to find the area. Let's say the points are -5 on the x axis, and -4 on the y axis, the area is 20, not -20.

EDIT: Doesn't quite work does it?

Srengam · 17 Apr 2012 at 18:51

TheCenturion said:
I can think of a real world example

Area is height x width.

If you're plotting something on a graph, and want to find the area. Let's say the points are -5 on the x axis, and -4 on the y axis, the area is 20, not -20.

All hail . . . .

Finally we got a real world example.