Why Cups are Frustrum-Shaped

So I noticed that some cups are shaped like frustrums or truncated cones. I looked up why and here(https://www.reddit.com/r/askscience/comments/2v151h/why_are_cups_cone_shaped/) it says that

1. They are easier to stack
2. They are easier to hold.

I am confused by the second point. Why would they be easier to hold? Wouldn't the holder need to bend the palm of their hand, making it harder to hold?

Thanks

• Why would they be easier to hold? ... perform an experiment ... decide for yourself Jan 18, 2023 at 8:30
• Another advantage of the conical shape of cups is that they are easier to manufacture: They are "drafted" making them easier to remove from molds. (If the cup is manufactured in a mold, e.g. glass or plastic.) Jan 18, 2023 at 13:32
• @Chris_abc That's an answer and probably more relevant than the others currently posted addressing mechanical integrity or ergonomics. Jan 18, 2023 at 14:43
• @DKNguyen I decided not to make it an answer because the OP specifically asked about "Why would they be easier to hold?". It would be an answer to the reddit thread though. Jan 18, 2023 at 15:32
• @Chris_abc I guess the OP is not familiar with vectors. aka it's easier to apply a vertical force to a horizontal surface than to apply a vertical force to a vertical surface. Jan 18, 2023 at 15:33

If the big end of the cone is upwards, then increasing your pinching grip on the cone would tend to slide the cup upwards, preventing it from falling.

If the big end is downwards, then increasing your pinching grip on the cone would tend to slide the cup downwards, encouraging it to slip from your grasp and fall.

TL;DR: it is due to the effect of a mechanical edge.

When you are holding a cup pressure is exerted by the fingers (essentially). Like the following image. Pressure is always normal to the surface.

That pressure results in a force (black arrow in image below) that if it is analysed in the vertical and the horizontal you get the following.

Common shape inverted shape

you will notice that the vertical component is opposite in those cases. I.e. when you increase the pressure the cup will be pushed downwards.

One thing that pop to mind (excuse the pun) wat the ice lollies (a type of frozen icecream in a cone shaped packaging) . If you ever held one of those and tried eat it, you know that you need to squeeze it, to make it pop out.

The principle is the same. If you inverted the cone then as you increased the pressure the glass would be pushed downwards (more easily that in the opposite case).

Final note: Lab glassware

One of the few exceptions, when an inverted cone shape is used is in Lab glassware like the following.

However you may notice that there is still a part of the glassware with a straight neck and also there is a visible bottle lip at the top (for lab clampers to be able to hold). The main reason that this the preferred shape, is that it secures the liquid in place and it enables easier stirring with little chance of spilling.

• Was seriously tempted to downvote this answer because you expand far too much energy on a really boring question. upvoted instead, gotta respect the energy.
– mart
Jan 18, 2023 at 7:56
• @mart I can't say I disagree. I mean I upvoted niels's answer as adequate. To my defense, it was a slow morning and this question conjured those different images so I decided to spend the time.
– NMech
Jan 18, 2023 at 8:05
• the sentece before the hr line stops abruptly. Not really an issue but hey.... Jan 18, 2023 at 11:59
• @NMech thanks! I agree with mart, you give too much for a very obvious and boring question, but I appreciate it. I'm confused about one thing in your post. You said Pressure is always normal to the surface. But I've had physics problems in school where it was like this: sketchpad.app/en. The weight of the object would be directed downwards at an angle to the surface, and we broke it into components perpendicular and parallel to the surface. Could you please explain this to me? Thanks! Jan 18, 2023 at 16:11
• I couldn't see your sketch, when I followed the link. So (assuming I understood what you are asking), is that in a physics problem you and you broke down the weight (not supporting forces) parallel and normal to the surface. This is the flip side of the coin. In any case, the parallel part to the surface is from the friction (for the icecream case friction is close to zero). The normal part is from the normal force from the support.
– NMech
Jan 19, 2023 at 10:47