# A pyramid is not a prism

Discussion in 'Mathematics' started by briceanus, Dec 19, 2010.

1. ### briceanusNew commenter

Anyone else get annoyed with The Apprentice ?
Maybe we should teach shapes and solids instead of getting them to play around with Toblerone boxes. Eh Beta ?

2. ### ResourceFinder

Nah ... he lost anyway

3. ### gcmaths

The other week one of them said big ben is '50 diameters in width' - is it really?!?

But yes the pyramid-prism thing did annoy me a bit...

4. ### ResourceFinder

We laughed like drains at Jamie and his 50 diameters

I think it quite worrying that NO-ONE commented on the prism pyramid thing ... not even Dara

5. ### rustybug

My blood was boiling! When I saw the bottle and heard that the main concept was to use the word "prism" to link in with there being 3 flavours I felt sure he would be slaughtered in the pitch or in the boardroom.
And NOBODY noticed!! Not one person said "That's not a prism, and the word prism has nothing at all to do with the number 3, you fool."
It looked like a perfume bottle, too.

6. ### DMNew commenter

It was well shaped for insertion into his uneducated backside.

7. ### DMNew commenter

Actually that suggests that a backside should be educated ...?!

8. ### ResourceFinder

Mine is ... how else could I talk out of it?

9. ### florapost

you fiends - i now have to go and watch the apprentice on i player!!!!

10. ### NazardNew commenter

I feel a twinge of embarrassment whenever I refer to something "weighing" a certain number of kg.
It took me a long time to overcome the desire to call a single 6-faced random-number generator "a die". I now use "dice" like the rest of the (English-speaking) world.
The one I absolutely can't/won't conform to, though, is calling the units of an area "cm squared". I have tried. It just doesn't feel right!

11. ### atics

I find your points here very interesting. I have a belief that as mathematicians we love things to be precise, and I also believe for most of us this extends also to being precise with language, however I know this is not a view shared by all.
As a relatively young teacher I don't believe I had the "old-school" grounding in correct grammar etc, and had to teach much of the finer points to myself. As such I feel frustrated that I was taught things which were imprecise or incorrect, such as "weighing" items or referring to "cm squared". I fight a constant battle with myself as to whether I should use the word "die" and risk fitting the stereotype of stuffy old-fashioned stickler maths teacher, or sacrificing my principles and use the word "dice" when I know it's wrong and it sticks in the throat, but makes it more accessible to students. What actually happens varies depending on how I'm feeling at the time.
With regard to prism/pyramid argument - I do feel this is subject-specific knowledge and something that most people in day-to-day life do not need to distinguish between and so can't be expected to know. Specialists in other subjects would no doubt be horrified by my lack of knowledge in some areas, so I don't feel we should be pompous and criticise people for not using mathematical language correctly.

12. ### rustybug

I felt the same annoyance I do when anyone confidently spouts any word without knowing what it means, I think.
My husband is an electronic engineer, educated in applied maths to a pretty high level, which he uses in real life every day, and he wasn't clear on the definitions of prism and pyramid (and didn't care about them either!) But I thought the clever chaps who work for Suralan would have looked into it and given him the chance to stick his knife in, and I guess I was disappointed that it never happened!
The one that I say differently in RL from in the classroom is "negative 6" in the classroom and "minus 6" outside, otherwise I get odd looks. However I cannot swallow "diamond" wherever I am.
What's the beef with "cm squared"? Is it that "square centimetres" is better? But I feel if you multiply y by y you get y squared, if you multiply cm by cm you get cm squared - if it's wrong it is at least helpful in teaching!!
I am ok with the word "weighing" as in the verb, but I'm afraid I still struggle to say "weight". And I am ashamed to say that if it slips out or if it's said to me I do point out that "mass" is a more accurate word, and you would need to multiply by 9.8 if you want to say "weight". I don't have many friends, as you've probably guessed.
It's all ridiculous, if I am going to get so het up over those things I would hardly ever dare speak in case I get a definition or a point of fact wrong.
I think I just expected more from the BBC.

13. ### rustybug

And I also mention that 9.8 is only accurate to 1dp, though many people use 10.
I think I sense a New Years' Resolution coming on??

14. ### NazardNew commenter

Yep - I agree.
Me: how do you measure the mass of an object?
Physics Teacher (PT): you put it on a mass scale.
Me: So the object is pulled down on top of the machine and it reads off the number of kilograms?
PT: Yep.
Me: Sounds like it's measuring _weight_ to me and then multiplying by nearly 10?
PT: Yes - but that gives the mass, so it's alright.
Me: [muttering] if you are at sea level. On earth. Not standing next to a big mountain. Etc...

So is there a proper way to measure "mass" then?

15. ### NazardNew commenter

I think (though happy to be proved wrong!) that the correct way to say it is "square cm", etc. It's just the usual convention... or at least it has been up until quite recently!
A possible sensible reason for this? If you have a square that has 5cm on each side then it is a "5 cm square", but this gets potentially confusing if the area is then quoted as being "25 cm squared". Using "25 square cm" gets round this issue entirely.
Agreed - not the biggest issue in the world!

16. ### ResourceFinder

Really?

I mean ... of course they do not need to know lots of things ... BUT ... pyramids and prisms are real things ... they are real different things

17. ### ResourceFinder

I say cms squared and cms cubed

Nothing wrong with them imo

You weigh an item to find its mass don't you?

18. ### KarvolOccasional commenter

The weight of an item depends upon where it is. For instance the "weight" of a rock will be different in outer space than it would be upon earth.
The mass of an object is immutable ( assuming nothing gets chopped off it etc. etc. )
In most cases they amount to the same thing, but they are not the same thing.

19. ### DMNew commenter

Scales don't measure weight. They measure normal contact force. Take some bathroom scales with you next time you ride a skyscraper lift and have fun!
And you mean dividing by nearly 10.
The usual way is to create a different force that is proportional to the mass. You could spin the object in a circle and measure the centripedal force. On the space station, they jiggle astronauts about on a springy chair. If the object has uniforn density, we could measure its volume of course.

uniforM