Workout: Reading the content in Bernoulli's principle


Read the web pages Bernoulli's principle and Reading the content in Bernoulli's principle


To give you some idea how this works, launch the PhET simulation, Fluid Pressure and Flow.

Set up

Select the Flow tab. Turn on the ruler, and make sure that friction is turned off. Press the + symbol at the lower right to turn on the display of the fluid density. Bring out the Speed and Pressure measuring tools. Your screen should look like the image below.

Answer these questions

  1. First, explore whether the program correctly conserves matter (water). The pipe has a default diameter of 2 meters. Use the little handles above and below the pipe to stretch the pipe to a narrower diameter of 1 meter. Our conservation equation says that the speed of the flow must adjust so that the total volume crossing an area perpendicular to the direction of flow should be constant. This suggests that the water has to travel through the narrower part of the pipe at a higher speed.

    Use the speed measurer to get the value of the speed in the pipe in the wider and narrower regions of the pipe. Use the continuity of flow equation to predict what the speed of the flow should be in the narrow region of the pipe. How accurately does the program represent the predicted speed in the narrower region?

  2. In order to speed up the fluid in the narrower region of the pipe, the pressure has to do work on the fluid and so the pressure should drop. Use Bernoulli's principle to predict what the pressure should be where the fluid is moving faster. Use the pressure measuring device to check it. How accurately does the program represent the predicted pressure in the narrower region?

Joe Redish 11/18/18

Article 776
Last Modified: November 11, 2019