Discovering Syringe Pressure & Suction: Small vs. Large Diameter Explained

  • Context: High School 
  • Thread starter Thread starter drsmith99
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SUMMARY

The discussion centers on the pressure and suction capabilities of syringes with varying diameters. It is established that pressure (P) is calculated using the formula P = f/A, where f represents force and A denotes area. A smaller diameter syringe generates higher pressure for a constant force due to its reduced area. Suction, defined as the movement of fluid from high to low pressure, is influenced by the syringe's volume rather than just pressure, with larger syringes capable of moving more fluid despite potentially lower pressure.

PREREQUISITES
  • Understanding of basic physics concepts, particularly pressure and force.
  • Familiarity with the formula P = f/A for calculating pressure.
  • Knowledge of fluid dynamics, specifically the concepts of suction and fluid movement.
  • Awareness of gauge pressure versus absolute pressure in fluid systems.
NEXT STEPS
  • Research the implications of syringe diameter on fluid dynamics and pressure generation.
  • Explore the relationship between syringe volume and fluid movement efficiency.
  • Study the differences between gauge pressure and absolute pressure in practical applications.
  • Investigate the effects of negative pressure in various fluid systems and its applications.
USEFUL FOR

This discussion is beneficial for engineers, medical professionals, and anyone involved in fluid mechanics or syringe design, particularly those interested in optimizing pressure and suction in practical applications.

drsmith99
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Hi, I have a simple question about syringes. I'm trying to find our which is able to generate more pressure with a given force, a syringe with small diameter, or one with a large diameter. An explanation with a simple formula would be much appreciated. Also which is able to generate more suction? Thank you.
 
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Hi drsmith99, welcome to PF

A small one:
P = f/A
where P is pressure, f is force, and A is area.

So for a constant force the pressure is largest if applied over a small area.
 
Thanks!
Any ideas about which generates more negative pressure or suction?
 
if you understood what the guy in second post replied you would have asked that :|
 
Try to see for yourself, assign variables to the equation, taking into account that you will use a vector for force (so, when sucking in, a 'negative force' is applied, making force a negative number). Keep the negative force the same, change the areas, and see what gives you a more negative pressure. Hope that helps!
 
drsmith99 said:
Thanks!
Any ideas about which generates more negative pressure or suction?
For negative pressure just use the formula above with a negative force.

However, suction is different from negative pressure. Suction is the movement of fluid from a region of high pressure to a region of low pressure. So, are you interested in just applying a negative pressure or in moving fluid? If moving fluid then the syringe with the biggest volume will move more fluid, even if it does so more slowly for a given force.
 
Just to clarify, there is no such thing as negative absolute pressure. A gauge pressure only appears to be negative since it is measured relative to atmospheric pressure.

CS
 
stewartcs brings out a good point. Because there is no such thing as negative absolute pressure the maximum negative gauge pressure you can even theoretically get is -1 atm. For a syringe with a given area that also implies a maximum force you can apply without just pulling the stopper out.
 

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