Bill Nye, The Home Run Derby, and sciency stuff

[Crash-n-Burn]

I'm hoping some of you watched the Home Run Derby last night. Bill Nye was in the commentator booth for a while and gave some insights on physics as they relate to baseball.

There was one topic that I found somewhat confusing - or contradictory to my understanding. Bill spoke to how a struck baseball will fly farther in hotter weather than cooler weather. (my kids started carrying on here a bit so I'm sharing what I recall but I likely missed some of his information) He explained that warmer air has greater moisture (humidity) and that water vapor is less dense than air, which in turn offers less atmospheric resistance to the ball. He did add that this phenomenon is somewhat negated by the ball absorbing moisture and becoming 'spongy' - that a dry ball is lighter and also transfers kinetic energy better than a wet ball.

This goes against my layperson understanding of rocketry physics. I've heard many people (including here) state that max altitude records should be attempted on dry, cold days. The stated reason for that is less atmospheric drag - the air is less dense.

I'd like y'all to take a crack at reconciling these seemingly conflicting principles. I have a couple thoughts:
1. I misheard Bill Nye on the HRD
2. Conventional wisdom on max altitude weather conditions is wrong
3. There is some nuanced difference between A and B that while both correct means they -
3.a - Don't need to reconcile (apples to oranges)
3.b - They do reconcile in a way I'm not seeing
4. Other

I am particularly interested in the science rationale, so kindly embed that in answers if possible. And thanks!

 

[Zeus-cat]

Hot air is less dense than cold air.

 

[neil_w]

This goes against my layperson understanding of rocketry physics. I've heard many people (including here) state that max altitude records should be attempted on dry, cold days. The stated reason for that is less atmospheric drag - the air is less dense.

That doesn't really make any sense. How could cold air ever be less dense than hot air? If that were the case hot air balloons would be never get off the ground.

As for the humidity, I remember quite clearly being taught in chemistry that humid air is less dense than dry air, despite the human perception that it "feels heavy". I presume the reason is because H20 molecules have less mass than the N2 molecules that they displace, but that may be an oversimplification (or flat out wrong ).

In any case, gonna side with Bill Nye here.

 

[jadebox]

Hot air is less dense than cold air.

And air with higher humidity is less dense.

Altitude record attempts are more likely to succeed in Denver, Colorado, versus here in Orlando, Florida. Humid air is less dense than dry air at the same altitude. But, the air is thinner, much less dense, a mile above sea level in Denver even when it is dry and cool. Since it is usually drier and cooler at higher altitudes, people associate those conditions with altitude record attempts.

But, a humid day in Denver would be better for an altitude record attempt than a typical dry day.

 

[Steve Shannon]

That doesn't really make any sense. How could cold air ever be less dense than hot air? If that were the case hot air balloons would be never get off the ground.

As for the humidity, I remember quite clearly being taught in chemistry that humid air is less dense than dry air, despite the human perception that it "feels heavy". I presume the reason is because H20 molecules have less mass than the N2 molecules that they displace, but that may be an oversimplification (or flat out wrong ).

In any case, gonna side with Bill Nye here.

You’re absolutely correct. Steam rises because it’s less dense.

 

[Steve Shannon]

And air with higher humidity is less dense.

Altitude record attempts are more likely to succeed in Denver, Colorado, versus here in Orlando, Florida. Humid air is less dense than dry air at the same altitude. But, the air is thinner, much less dense, a mile above sea level in Denver even when it is dry and cool. Since it is usually drier and cooler at higher altitudes, people associate those conditions with altitude record attempts.

But, a humid day in Denver would be better for an altitude record attempt than a typical dry day.

Exactly!

 

[Crash-n-Burn]

Thanks folks, that was pretty straightforward after all. It would appear that I picked up some invalid assumptions along the way.

 

[Steve Shannon]

Thanks folks, that was pretty straightforward after all. It would appear that I picked up some invalid assumptions along the way.

Don’t feel bad. Many people (including one science teacher I know) make the assumption that humid air is denser than dry air; after all, water is denser than air, right? “The air just feels thick!” I’ve heard people say when the humidity is high.

 

[prfesser]

I'm hoping some of you watched the Home Run Derby last night. Bill Nye was in the commentator booth for a while and gave some insights on physics as they relate to baseball.

There was one topic that I found somewhat confusing - or contradictory to my understanding. Bill spoke to how a struck baseball will fly farther in hotter weather than cooler weather. (my kids started carrying on here a bit so I'm sharing what I recall but I likely missed some of his information) He explained that warmer air has greater moisture (humidity) and that water vapor is less dense than air, which in turn offers less atmospheric resistance to the ball. He did add that this phenomenon is somewhat negated by the ball absorbing moisture and becoming 'spongy' - that a dry ball is lighter and also transfers kinetic energy better than a wet ball.

This goes against my layperson understanding of rocketry physics. I've heard many people (including here) state that max altitude records should be attempted on dry, cold days. The stated reason for that is less atmospheric drag - the air is less dense.

I'd like y'all to take a crack at reconciling these seemingly conflicting principles. I have a couple thoughts:
1. I misheard Bill Nye on the HRD
2. Conventional wisdom on max altitude weather conditions is wrong
3. There is some nuanced difference between A and B that while both correct means they -
3.a - Don't need to reconcile (apples to oranges)
3.b - They do reconcile in a way I'm not seeing
4. Other

I am particularly interested in the science rationale, so kindly embed that in answers if possible. And thanks!

Yes, hot air is less dense than cold air. And warmer air usually has more H2O(gas) than cooler air; since the molar mass of H2O is less than the average molar mass of the N2/O2/Ar/pollution we breathe, that also leads to a reduction in density...but it ain't much. So in theory, a hot, humid day with the lowest possible atmospheric pressure is the best condition for altitude.

But remember: "In theory, there's no difference between theory and practice. But in practice, there IS."

 

[jadebox]

Sometime ago I was corrected online after I suggested that dry air was less dense. I don't recall exactly when or where or how it came up in the discussion. But, that was what caused me to do a little research to confirm that humid air is less dense. In some ways it still seems counter-intuitive because water is denser than air.

But, individual water molecules weigh less than Oxygen molecules and less than Nitrogen molecules. Air is mostly N2 and O2. So, as long as the temperature remains the same, air will weigh less the more water molecules there are in the air.

But ... but ... what if you increase the water content of the air until the air is 100% water? Ha! Obviously, that would be much denser than air.

Well, yeah. But, it would not be air anymore. It would be water and I have already conceded that water is denser than air. So, there, smarty pants. Pfffft!

Actually, air can't be more than about 4% water vapor. At normal temperatures, water condenses once the amount of water vapor rises to about 4%. So, you can't increase the amount of water in the air above that because you would get water and air rather than just air.