Physics Help Forum Dynamic Spring Plunger System Help
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Mar 24th 2018, 05:28 PM   #11
Junior Member

Join Date: Mar 2018
Posts: 9
No worries! That is a correct description; however, the tube at the end of the syringe/nozzle will have a very small radius and relatively large length length, and thus, I believe, will impose a very high and significant resistance.

Again, I appreciate the time you're taking to go through this with me!

Many thanks!
J

 Originally Posted by studiot I have had a rethink about this problem an now think that I made it a bit overcomplicated with my equation of motion (which is correct but not needed) My apologies. As I understand the system, the plunger is pushed by the spring, which must therefore be precompressed so that it can push the plungers as it expands towards its equilibrium postion. As the spring expands it exerts a diminishing force on the plunger, causing a reducing pressure on the fluid in the barrel of the syringe. The fluid is thus forced out through the nozzle under a reducing pressure regime so exits at a continually reducing rate. Under these circumstances an appropriate question is not how much fluid is discharged in a given time, but how much time is taken to discharge a given (presumably prescribed) amount of fluid. Calculating this involves integrating the Torricelli equation I mentioned earlier, over time and under reducing head conditions. If you are happy with this description I will post a sketch and some mathematics tomorrow.

Mar 30th 2018, 05:22 PM   #12
Junior Member

Join Date: Mar 2018
Posts: 9
Hi studiot,

I was wondering if you had a chance to think this through.

Thanks!
J

 Originally Posted by aculaMD No worries! That is a correct description; however, the tube at the end of the syringe/nozzle will have a very small radius and relatively large length length, and thus, I believe, will impose a very high and significant resistance. Again, I appreciate the time you're taking to go through this with me! Many thanks! J

Apr 19th 2018, 07:02 AM   #13
Junior Member

Join Date: Mar 2018
Posts: 9
Hi studiot,

Just wanted to check in again to see if you had some time to rethink this.

Thanks!
J

 Originally Posted by studiot I have had a rethink about this problem an now think that I made it a bit overcomplicated with my equation of motion (which is correct but not needed) My apologies. As I understand the system, the plunger is pushed by the spring, which must therefore be precompressed so that it can push the plungers as it expands towards its equilibrium postion. As the spring expands it exerts a diminishing force on the plunger, causing a reducing pressure on the fluid in the barrel of the syringe. The fluid is thus forced out through the nozzle under a reducing pressure regime so exits at a continually reducing rate. Under these circumstances an appropriate question is not how much fluid is discharged in a given time, but how much time is taken to discharge a given (presumably prescribed) amount of fluid. Calculating this involves integrating the Torricelli equation I mentioned earlier, over time and under reducing head conditions. If you are happy with this description I will post a sketch and some mathematics tomorrow.

 Tags dynamic, plunger, spring, system

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