# A force exerted on a plastic ball in a rubber tube

• Lidor
In summary, the force needed to remove a plastic ball from a rubber tube depends on the elasticity of the materials and the coefficient of friction between them. The size of the hole is not as important as the properties of the rubber. Engineering diagrams and detailed information about material moduli and coefficients of friction are necessary to accurately determine the force needed. The diameter of the tube can expand when compressed and shrink when stretched, making it easier to push a ball through than to pull it out.

#### Lidor

Hello,
How can I calculate the force that must be exerted on a ball inside a rubber tube?

Thanks

With a problem specification that vague, you can't. Is this a homework question? If so, repost in the homework section and answer the questions in the template (provide the exact question, for starters). If not, explain what you want to do with the ball.

Diameter plastic ball - 11mm
Diameter rubber tube - 10.5mm
Length rubber tube - 15mm

the plastic ball is stack in the rubber tube,
What is the force you need to exert to get the plastic ball out of the rubber tube?

Depends on how elastic the rubber tube and ball are, what the coefficient of friction between the two is, how far in the ball is, and probably other things I haven't thought of. It probably also matters how you are planning to apply the force - blowing into the other end of the pipe, squeezing it out like peristalsis or just grabbing the thing and pulling.

I suspect this is one of those situations that's way too complex to model with basic physics. I'd suggest reporting your opening post (there'a a link at the bottom of it) and asking for the thread to be moved to one of the engineering forums. This is the kind of thing they might have data tables for, compiled from practical experience rather than derived from physical theory.

russ_watters
Put some soapy water in the tube to try to reduce the friction.

russ_watters and sophiecentaur
@Lidor This could be a very hard problem because any force on the tube will change its bore size - whether you are pushing or pulling it. Have you tried any experimentation?

sophiecentaur said:
experimentation

yes indeed,
I'll be more precise
Suppose I have a circular gasket with a ball bearing and between them there is a minimum friction (for example, a 11 mm diameter ball and an inner diameter gasket of 10.5 mm)
What force do I have to exert in order for the ball to pass through the gasket?
I would also love to have guidance on what study material I should read

Thanks

Lidor said:
yes indeed,
I'll be more precise
Suppose I have a circular gasket with a ball bearing and between them there is a minimum friction (for example, a 11 mm diameter ball and an inner diameter gasket of 10.5 mm)
What force do I have to exert in order for the ball to pass through the gasket?
I would also love to have guidance on what study material I should read

Thanks
It depends as @Ibix said. The ball has to get smaller or the gasket bigger. That depends on elasticity: how much force to you need to make it smaller or bigger? That depends on the rubber. Soft rubber needs little force. Hard rubber needs a lot of force.

So the size of the hole is not as important as the properties of your rubber.

. . . . . and the materials and dimensions of the tube; how much is the gasket compressed in order to accommodate the ball?
Engineering diagram required plus a lot of details about the moduli of the materials and the coefficient of friction between the two surfaces.

Lidor said:
What is the force you need to exert to get the plastic ball out of the rubber tube?
Notice how a plastic or rubber hose can be pushed onto a hard tube connector, but cannot be pulled off as easily. That is because the tube diameter expands when compressed and shrinks when stretched length-ways. The opposite is true when the soft tube passes inside a restriction, it cannot be pushed in easily, but it is easy to pull the tube out.

You can blow a ball through a tight tube as the pressure expands the tube away from the ball as the ball moves forward, But you cannot suck the ball through, as the tube shrinks against the front of the ball.

anorlunda