Answer, and give a reason. A shower curtain moves inward when the shower is running fast.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Answer, and give a reason.
- A shower curtain moves inward when the shower is running fast. Why?
- Why should you stand back from the edge of a railway platform when a fast train passes?
- A table tennis ball floats in the stream of air from a hair dryer pointing up. Why does it not fall out sideways?
Need a reminder? The key ideaShow
Bernoulli's equation: along a streamline of an ideal fluid in steady flow, is the same. In a level pipe, : faster means lower pressure.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The moving water drags air along inside the shower, so the air pressure there drops below the still air outside, which pushes the curtain in.
Step 2. (b) The fast air beside the train has a low pressure; the still air behind you pushes you toward the train.
Step 3. (c) If the ball drifts sideways, the faster air on the side nearer the middle of the stream has a lower pressure, and the still air outside pushes it back.
Answer: In each case, fast air has low pressure and the slower air pushes.
Watch out. It is the higher pressure of the still air that does the pushing.
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