# A Friction in a syringe

Tags:
1. Dec 21, 2017

### Stephen0311

Hi Friends,

So I'll go into a bit of the setup that I'm having some trouble figuring out. I have a piece of rubber that will be pushing up against the side of a metal (or plastic) container to create a waterproof seal. The easiest way to think about this would be to imagine the rubber piece of a syringe that is pushed up and down. Basically I'm trying to determine the force I need from a spring to have that rubber interior move about three inches.

When I'm looking at the formulas for friction, all of them reference a coefficient of friction (but it's always a given in example problems). Is there a way to calculate the force of friction of the sliding waterproof seal I mentioned above?

Thanks for the help

2. Dec 21, 2017

### Staff: Mentor

Edit: Sorry, you can't calculate the coefficient of friction. It is a quantity measured by experiment.

But I did find a paper that might help you. Friction Forces in O-ring Sealing

3. Dec 23, 2017

### CWatters

Best bet is to measure the required force. You will need to preload the spring so it continues to generate the required force right to the end of the required travel. This means it will generate more force than needed at the start of the travel.