Suction Cups

[spciesla]

I don't need real help here, just a curiousity. In my shower, I have a soap dish that is supported by two suction cups (approx. 1" diameter). It doesn't always do a good job holding up a new bar of soap. It made me wonder how I would calculate the force/moment that a suction cup can support.

What do you think?

 

[MiketheEngineer]

I think you need to spend more time singing in the shower...

Has a lot to do with the surface finish, lubricant if any, condition of cup, etc.

I have used rather large suction cups (8'' to 10'') to lift some heavy steel plates. Always made sure my feet were clear!!

Interesting subject

 

[dgowans]

A quick Google search on "vacuum force" led me to this site:

http://www.edcousa.net/vacuum-training.html

Looks like there might be a lot of useful information here, although I didn't wade too deeply.

 

[KENAT]

Lots of factors as Mike points out.

Friction on the surfaces (hence lubricant or surface finish) is one factor. (Interestingly though a smooth surface may provide a better seal on the vaccuum than a very rough one so you can't take it to extremes.)

Size of cup.

Level of 'vacuum' induced (force = pressure difference x area of cup) it's never a full vacuum but a relatively small pressure difference can produce significant load.

In the kind of suction cups you're talking about I suppose you're relying on the elasticiy of the cups trying to pull away from the surface and resume their original shape to generate the 'vacuum'. I'm not sure how you'd simplistically be able to calculate this value.

You could test it though by pulling on the cups (or article with the cups) with either a peak force newton meter (if you have a regular one with a sliding indicater you can put masking tape across the slot and it tears up to the peak force) or by hangind it upside down and dangling weights on it.

KENAT, probably the least qualified checker you'll ever meet...

 

[Newmanite]

Put it on a piece of rope and hang it over the tap