Action reaction force quick question

AI Thread Summary
In the scenario of a firewoman using a hose, the action force is the water being pushed forward, while the reaction force is the air pushing back against the water. The firewoman also exerts a force on the hose to keep it steady, which has a corresponding reaction force. In a vacuum, the absence of air means there would be no air resistance, but other action-reaction pairs, such as the hose exerting force on the water, still apply. The discussion emphasizes that the labels "action" and "reaction" can be interchangeable in these force interactions. Understanding these dynamics is crucial for grasping the principles of action-reaction forces.
Adam17
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Homework Statement

A firewoman opens the fire hose, and water sprays forward. What is the action force and reaction force?



Homework Equations

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The Attempt at a Solution


I was thinking that the action force would be water pushing on air and reaction air pushing on water? But how would this be possible in space where there is a vacuum?
 
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I think the question is rather ambiguous. The firewoman exerts a force on the hose to hold it at rest. There will be a corresponding reaction force. Can you describe this reaction force?

Also, the hose will exert a force on the water. What is the reaction force to this?

As you stated, the water will exert a force on the air as it moves through the air. And you correctly stated that the reaction force would be the air exerting a force on the water.

[By the way, when dealing with action-reaction pairs, it doesn't matter which of the two forces you call the "action" force and which the "reaction" force.]

If the hose and firewoman are in a vacuum, then of course there would be no force of the water on any air. But you would still have the other action-reaction pairs mentioned above.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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