To prove that, you need combination of mass balance and mechanical energy balance (i.e. bernoulli equation). mass balance: mass rate in = mass rate out. Assuming incompressible fluid (same density in and out), since mass rate = volume rate * density, density get canceled out and the result is volume rate in = volume rate out. It is also known that volume rate = velocity * Area. From this you can prove that, if area is decreased (such as, putting your thumb on the hose), velocity will increase. Then you will need bernouli equation. Simplified Bernoulli Equation: (P1/density) + (Velocity1^2/2)+ (gh1) = (P2/density) + (velocity2 ^ 2/ 2) + (gh2) Assuming h (height) is the same, they get canceled out. Then, you will have an equation with only P (Pressure) and V (velocity) as variables which you can use to prove that if V2 increases, P2 decreases, provided P1 and V1 are constant. So, volume rate at location 2 is not dependent on Pressure at location 2, provided same pressure and volume rate coming in. It "feels" like pressure increasing, but rather it's velocity that is increasing or kinetic energy increases. Check out these sites http://physics.bu.edu/py105/notes/Bernoulli.html http://rabi.phys.virginia.edu/HTW/water_distribution.html For the second question, you might not be able to use same exact equations for air, since air might be considered as compressible. It may involve more complicated equations. Rummy Makmur Process Engineer Ibiden Circuits of America -----Original Message----- From: Eric Christison [mailto:[log in to unmask]] Sent: Tuesday, November 13, 2001 3:27 AM To: [log in to unmask] Subject: Re: [TN] Formula? I think you're all barking up the wrong tree. Bernoulli's equations shows the conservation of kinetic energy in fluids and is generally used to calculate things like areodynamic lift on an aerofoil or the forces exerted on a pipe wall as the the contents flows round a corner. I think you're searching for P1v1/T1 = P2v2/T2. However v is not volume but specific volume ie m^3/Kg. Spend a minute on a reality check. If you put your thumb on the end of a hose pipe does the pipe get smaller? If not, how can the volume of the pipe decrease? Hope this helps, [log in to unmask] wrote: > > Ray, try http://www.lmnoeng.com/Flow/bernoulli.htm > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]]On Behalf Of Golembiewski, Ray > Sent: Monday, November 12, 2001 14:34 > To: [log in to unmask] > Subject: [TN] Formula? > > What is the formula that proves when I put my thumb on the end > of a garden house, the pressure increases and volume decreases. Is the > same formula used with air? Please help, > > Ray Golembiewski C.I.D. > Manufacturing Test Engineer > Projects Unlimited, Inc. > (937) 918-2200 > -- Eric Christison Mechanical Engineer STMicroelectronics 33 Pinkhill Edinburgh EH12 7BF Tel: (0)131 336 6165 Fax: (0)131 336 6001 ---------------------------------------------------------------------------- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------