Friction coefficient and the force on a syringe plunger

[Huger]

Homework Statement

I need to conduct an experiment and measure how what is the coefficient and force of friction of the rubber that pushes down along the edge inside the syringe. The thing is I can’t use a dynamometer.

Relevant Equations

?

I need to conduct an experiment and measure how what is the coefficient and force of friction of the rubber that pushes down along the edge inside the syringe. The thing is I can’t use a dynamometer.

 

[BvU]

Hello Huger, $\qquad$ $\qquad$ !

can’t use a dynamometer

Voluntary restriction ?
Alternatively you could use a lever or a weight instead of your thumb

Are you aware of the difference between static friction and dynamic friction ?

And: what's in the syringe ? air, water, glycerine ?

 

[Huger]

Hello Huger, $\qquad$ $\qquad$ !Voluntary restriction ?
Alternatively you could use a lever or a weight instead of your thumb
View attachment 253382
Are you aware of the difference between static friction and dynamic friction ?

And: what's in the syringe ? air, water, glycerine ?

It’s air inside

 

[berkeman]

Welcome to the PF.

Homework Equations: ?

Why have you not posted the obvious equations that relate to frictional forces?

And are you to assume the end of the syringe is open? Does it have a needle on it? If so, what gauge needle and why does that matter?

 

[haruspex]

It’s air inside

When not using a dynamometer, the tricky part is only measuring the frictional force, not including any additional force leading to an acceleration. But since you want kinetic friction, there must be motion.
Coefficient is rather tougher. How are you going to assess the normal force (per unit of arc)? If I had this problem to solve in the real world, I would measure the coefficient of friction between the two materials in a different set up (where the normal force is known, say a block sliding on a glass plate, with a weight on the block) then, from the force needed to push the syringe, deduce the normal force.

Fwiw, if you only wanted to find the normal force you could set up the syringe and the block on a plate in a back-to-back arrangement. Push the two together and see which slides. Adjust the weight on the block until it is borderline which slides.

 

[BvU]

@Huger : can you enlighten us about purpose and context ?
And: why air ?

 

[haruspex]

@Huger : can you enlighten us about purpose and context ?
And: why air ?

Presumably it is air in order to avoid complications arising from back-pressure from the fluid. However, it might matter whether the sides are dry or wet.