# Have a cone and divide it into infinately small slices

1. May 18, 2004

### Lorentz

If I have a cone and divide it into infinately small slices. Wouldn't both sides of one slice have the same area and wouldn't the next slice (and so on) have the same area as the slice before. So wouldn't your cone actually be a cylinder?

My answer is no, because the reasoning is wrong. If I had infinately small slices I would never complete the cone/cylinder in the first place. And the assumption of both sides having the same area is an assumption to be able to integrate, but is not reality. If we're talking about the perfect cone then both sides of the slices should have different areas even if the slices were infinately small.

2. May 18, 2004

### AKG

It would something more like, as the number of slices approaches infinity, the width of each slice approaches zero, and the areas on the two faces of the slice approach each other.

Here's something to think about. You should know that a line is made up of infinite points. Each point has zero size. So, given an infinite number of zero-sized points put together, how is it that you get a line with non-zero-size?

Well, be careful here, because you can't really make any arguments "from reality" when dealing with math. Math is a useful tool in modelling reality, but that doesn't mean that it is based on reality (it is based on its own axioms, some of which seem rather unnatural), nor does it mean that it is an accurate tool in modelling reality.
What does it mean to be infinitely small? Can something be smaller than infinitely small? What would the difference in area be between the two faces?

3. May 18, 2004

### Lorentz

erm... the difference would be infinitely small? But that would still be a difference which makes it possible to glue the slices together and get the cone back again rather then a cylinder. If the difference would be zero we would get the cilinder.

4. May 18, 2004

### Lorentz

This question just popped into my mind: Is there a difference between infinitely small and zero?

5. May 18, 2004

### HallsofIvy

Yes, IF you are working in "non-standard analysis" and, by "infinitely small", you mean "infinitesmal". Otherwise "infinitely small" is just a (misleading) shorthand for "in the limit".