A falling steel ball

Classical Mechanics Level 1

Will a steel ball with a mass of 5 kg 5\text{ kg} fall faster through H 2 O \text{H}_2\text{O} at 4 0 ∘ F 40^\circ F or 2 0 ∘ F ? 20^\circ F?

It makes no difference 4 0 ∘ F 40^\circ F 2 0 ∘ F 20^\circ F

T P by T P , 19, Philippines

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6 solutions

T P
Feb 6, 2016

At 2 0 ∘ F 20^\circ F the water will be ice, which means that it will not fall through at all. Therefore, the answer is 4 0 ∘ F 40^\circ F .

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Not necessarily, it depends on air pressure too. But the colder water would still be denser, so I think that would maybe provide some extra resistance?

Hobart Pao - 5 years, 4 months ago

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Yeah, that was the logic I applied.

Mehul Arora - 5 years, 4 months ago
Mattia Palumbo
Feb 11, 2016

It depends on viscosity. In fact viscosity and temperature are inversely proportional so, if the temperature is higher, there will be smaller opposition to the motion by the fluid.

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Isn't the assumption that water is an inviscid fluid?

Paul Walls - 5 years, 4 months ago

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I don't see this assumption in assumptions.

Mattia Palumbo - 5 years, 4 months ago

That is the actual logic as it explains flow of charges through metal.

Naveed Ashraf - 5 years, 4 months ago
Dion Sukhram
Feb 11, 2016

It doesn't matter about the density, the only thing that matters is that it would be below freezing at 20 degrees

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Jason Hatch
Feb 11, 2016

20 degree Fahrenheit water is ice last time I checked.

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Robert Wilson
Feb 11, 2016

The 20 degree water is colder and will therefore be denser. This means it will exert a bigger reaction force on the ball, slowing it down.

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Reeshabh Ranjan
Feb 11, 2016

Maybe Stoke's Law applicable here?

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