Understanding Why a Feynman Sprinkler Does Not Turn in Reverse

The Feynman Sprinkler is a thought experiment that illuminates some fascinating principles in physics, particularly related to fluid dynamics and momentum. While ' target'_blank'>videos often illustrate its opposite behavior, this does not reflect the expected outcome.

Key Concepts and Physics Behind the Feynman Sprinkler

Action and Reaction: The classic setup of the Feynman Sprinkler involves water being expelled through nozzles. This expulsion according to Newton's Third Law (for every action, there is an equal and opposite reaction) should cause the sprinkler to turn in the opposite direction. However, when you attempt to run the sprinkler in reverse, sucking water in instead of expelling it, the expected turning does not occur.

Fluid Dynamics

When water is sucked in, the flow dynamics change. Sucking in water creates a low-pressure zone around the nozzles rather than the high-pressure conditions associated with expulsion. This different flow pattern does not produce the same reaction force that expulsion would, leading to no significant turning of the sprinkler.

Momentum Conservation

In the case of sucking water, the system does not gain the same momentum as it would when expelling water. The water entering the nozzles does not exert a significant force on the sprinkler. Essentially, the water entering the nozzles does not generate a reaction that would cause the sprinkler to spin.

Experimental Observations and Misconceptions

Video demonstrations of the Feynman Sprinkler turning in reverse may be influenced by various factors:

Imperfect Setup

If the apparatus is not perfectly designed or there are leaks, the observed behavior may not align with theoretical expectations. Imperfections in the setup can lead to misleading results.

External Forces

Any external forces, such as manual twisting or movement, can create the illusion that the sprinkler is turning in reverse. These external inputs can override the intended physics.

Misinterpretation

Misinterpretation of the experiment may arise from the way it is presented. Factors such as filming angle, pace, and cut-editing can create a misleading perception.

Conclusion

The Feynman Sprinkler does not turn in reverse due to the differences in fluid dynamics and the lack of momentum transfer when water is sucked in. Any videos showing reverse turning may not accurately reflect the underlying physics or be influenced by external factors.

Understanding the principles of action and reaction, fluid dynamics, and momentum conservation helps clarify why the Feynman Sprinkler behaves as it does. Further experiments can provide a deeper insight into the physics behind these phenomena.