# I Bernoulli vs Energy Conservation?

1. Mar 27, 2016

### gamz95

In the example, is it possible to have same velocities at the two ends of the tube? How would you construct energy conversation equation?

2. Mar 27, 2016

### sophiecentaur

Why would you expect mechanical energy to be conserved if there is any turbulence involved? Same velocities doesn't imply no energy loss.

3. Mar 27, 2016

### Staff: Mentor

The problem statement does say "frictionless... flow."

4. Mar 27, 2016

### Staff: Mentor

It is shown right in the solution they gave. If you look at their final equation, it's just F = ma.

5. Mar 27, 2016

### gamz95

Yes it is indeed frictionless. Therefore, when normal energy equation constructed the KE1=KE2(Since it says that velocities are the same). However, how is this physically possible? And question gives a changing velocity profile(not a constant velocity).

6. Mar 27, 2016

### Staff: Mentor

If you take the transient 1D momentum equation and integrate between the two ends of a control volume in which the velocity within the control volume is changing with time (and possibly position), you get the ordinary Bernoulli terms plus a term involving the rate of change of momentum with time within the control volume. See the PDF at Unsteady Bernoulli Equation - MIT OpenCourseWare that can be reached by googling transient Bernoulli equation.