Speed of Flow in a Straight River

Let's take a look!

Watch the video on YouTube.

What type of experiment is this?

Experimental procedure and explanation:

• We use the following model of a river to observe the flow. The river width is 12 cm and the depth is constant at approximately 1.5 cm. An underwater pump is used to make the water flow. (The narrator in the video says “underwater motor” but this is a mistake窶琶t is actually an underwater pump.)
• To investigate the flow speed, we added higher alcohol particles (with diameters of approximately 0.5 to 1 mm) and observed the flow. “Higher alcohol” is the name of a group of substances, and the particles used in this experiment are often used as detergents. They are not related to expensive alcoholic drinks!
• In the straight part of the river, the water flows at approximately the same speed everywhere. A stream like that modeled here, which flows in the same direction at the same speed everywhere, is called uniform flow.
• However, if we investigate the flow more closely, we find that the flow is affected by viscous friction near the stream’s bottom and the side walls, and therefore these parts flow more slowly. The area of slow flow near the walls is called the boundary layer.
• The same experiment can be performed using small scraps of paper instead of particles. Particles made from Styrofoam or similar materials do not work very well because such materials are affected by static electricity.

[Keywords]	Uniform flow
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