Mythbusters 2/1/06 (Helium filled Football)

[5thcrewman]

Does anyone still watch this? Does the fact that the narrator doesn't know the diff. between 'farther' and 'further' bother anyone else?

[bentleyml]

I still watch the show and had fun.

[doom1701]

Does anyone still watch this? Does the fact that the narrator doesn't know the diff. between 'farther' and 'further' bother anyone else?

There's a difference?

It's probably the only show that we watch every week without fail. And it continues to leave us wanting more. This episode was another good one (although, like most eps recently, a little too heavy on the build team). I said to my wife early on in the show


The helium one probably won't go as far as the air filled one--it's more about mass and inertia than about weight.


I'm glad I was right. :)

[Chapper1]

But I did find it interesting that the mass of the footballs were less than the football itself with nothing in it...

[jrinck]

I haven't seen this episode yet, but if you ask me which would go further if thrown, an air filled football or a Helium filled football, I'd have guessed the air-filled one.

It would have to do with the grip. Gripping a heavier object is easier than a lighter one, at least with the weight difference we're talking about here. The Helium balloon would be more likely to slip out of your hand.

But what about kicking? I'd guess the Helium one might be able to go higher, but not necessarily further.

I say that this is more of a Z-axis question than it is an X-axis question.

[mgar]

But I did find it interesting that the mass of the footballs were less than the football itself with nothing in it...

I didn't watch the show, but that doesn't make any sense. The mass of an empty football is less than the mass with anything in it, including helium. Perhaps the weight is different because the weight on a scale is equal to the force of gravity minus buoyancy. Buoyancy is a function of volume, and the empty ball with have less volume than the filled ball.

[srs5694]

But I did find it interesting that the mass of the footballs were less than the football itself with nothing in it...

Actually, that's not correct. Mass is a measure of the amount of matter in an object, whereas weight is a measure of the force the object's mass exerts as a result of gravity. Assuming a constant gravitational field, the two are highly correlated -- in fact, weight is defined as mass times the acceleration of gravity. In the case of this particular show, though, the measured weights of the helium-filled footballs were less than the measured weights of the empty ones because the helium is lighter than air, and so exerts a buoyant force that partially counteracts the weight of the football itself. If I'm reading my definitions correctly, this means that their weight measurements were inaccurate for the helium-filled footballs. At the very least, it means that weight cannot be used as a stand-in for mass for the helium-filled footballs.

For the most part, the show didn't go far wrong on this point, aside from their goof when weighing the footballs, which could be attributed to an oversimplification. At one point, though, they were talking about the physics of football throwing and they used the term "weight" when the actual theory and equations, if I recall correctly from high school, refer to mass. Between this and the fact that they then used their measured (and technically incorrect) weights, I think they fell down on the scientific explanation side of this one. That's not to say I doubt their results, though, which were null.

On the plus side, I was pleased to see that they finally did some statistics. This wasn't the first episode where I was thinking "t-test! T-test!" ;) It looks like they finally did one, although they didn't identify it by name.

[vertigo235]

Yes, he's mixing up weight and mass

[5thcrewman]

I was hoping for a follow up test with a heavier than air gas that would show how the weight of the ball influences the 'hang time.' Maybe they could have used some of that super heavy Eiffel Tower air they mentioned! :D

SPOILER: Next week the Ex-Mythterns test the 'Step on a Crack- Break your Mother's Back' myth!! :rolleyes:

[Church AV Guy]

I thought that they had mixed up momentum and inertia at one point, but after thinking about it I decided that what they said was okay. I too thought filling the footballs with a heavier than air gas might be interesting, but that wasn't really the myth, was it.

Watching the pig's teeth being broken in slow motion was dis-gusting! I'm surprised Kari didn't just walk off the set! I might have been tempted to if I had been there. Catch a bullet with your teeth? Surely some myths are too stupid to even wast the time testing them. Maybe the guy in the film was using a VERY light load of gunpowder in the shell. I don't think they examined that possibility. On the other hand, if they couldn't even catch a paint ball, how could they catch even a lightly loaded bullet?

[Chapper1]

Yes, he's mixing up weight and mass

I knew something had to be wrong in what I heard. I picked yours to quote because that other post pointing that out was just to complicated for me to follow!! :D

[The Flush]

I remember about 10 years ago when Jackie Sherrill, then the head football coach at Miss St, accused Auburn's punter of using a helium filled ball becuase he got off a couple booming 70 yard punts against MSU. Even back then most people thought that was a stupid theory. The kid just had a career night, that all.

[mgar]

I didn't watch the show, but that doesn't make any sense. The mass of an empty football is less than the mass with anything in it, including helium. Perhaps the weight is different because the weight on a scale is equal to the force of gravity minus buoyancy. Buoyancy is a function of volume, and the empty ball with have less volume than the filled ball.

I finally watched the episode. There was no mention of the mass of the football, only the weight. There were technically correct without going in depth on the subject. Most people aren't interested in a long discussion about volume, mass, weight, buoyancy forces, gravity forces, etc.

[danieljanderson]

Why didn't they measure "hang time" as a separate element? Isn't it possible that the hang time could still be greater than a traditional ball?

[doom1701]

Why didn't they measure "hang time" as a separate element? Isn't it possible that the hang time could still be greater than a traditional ball?

In my feeble scientific mind, it should make no difference. Hang Time is a result of two things--the force (or acceleration, to be more accurate) imparted onto the ball, and gravity. They made sure that the acceleration imparted on the ball was the same for both. That means that the ball was travelling at the same speed, no matter what the ball was filled with.

Once the ball is moving, it's just a function of gravity to bring it back down--and gravity "pulls" at the same speed no matter what the weight of the object is. So the ball is going to spend the same time in the air no matter what, as long as it was thrown at the same speed.

The two hiccups are the mass/inertia issue, which could allow a "heavier" ball to fly further, but not attain more hang time (unless the spin does impart lift--wasn't clear on that), and the force that can be imparted by a real kicker or thrower. The throwing machine really wasn't affected by a couple of grams either way, but it's possible a real person could be--causing less force to be imparted onto the "heavier" ball because of both inertia at rest and plain old strength. But I doubt that a couple of grams would matter for an experienced football player, either.

[BrettStah]

I watched this, but may have missed a little bit, because I still have a question... why was the acceleration imparted on both the regular and helium balls identical? I would have guessed that the lighter (helium) ball should be sent flying at a faster rate. For an exaggerated example, imagine a football filled with lead, and one filled with air. The one with air would accelerate faster than the one with lead, given the same amount of force, right? So the lighter helium-filled ball should go faster too. At least that's what popped in my head during/after this episode. :)

[billboard_NE]

What about the bullet in the teeth myth? Next week are they going to see if its possible to turn a beautiful assistant into a white tiger? wow they must be out of ideas. And instead of changing the micrsecond timer why didn't they move the table holding the teeth forward to the point where the bullet was at the time of the teeth closing?

[doom1701]

I watched this, but may have missed a little bit, because I still have a question... why was the acceleration imparted on both the regular and helium balls identical? I would have guessed that the lighter (helium) ball should be sent flying at a faster rate. For an exaggerated example, imagine a football filled with lead, and one filled with air. The one with air would accelerate faster than the one with lead, given the same amount of force, right? So the lighter helium-filled ball should go faster too. At least that's what popped in my head during/after this episode. :)

For the throwing machine, you're looking at a device that is going to impart X speed to a ball. As long as the ball is within a certain weight range as to not strain the machine, it's going to throw the ball at the same speed no matter what it's weight. Sure, if you put a 10 pound football into it, the results would be different, but a machine made to throw a x oz football at y speed is going to throw a x-3 oz football at the same speed.

[mportuesi]

What about the bullet in the teeth myth? Next week are they going to see if its possible to turn a beautiful assistant into a white tiger? wow they must be out of ideas.

Indeed. "Bullet in the teeth" was another exercise in proving the obvious. I was really disappointed with this segment of the show. The method used in a lot of the experiments was flawed. Only the fact that it's pretty easy to prove this myth is false saved them from their own bad experiments.

I did really like the football myth. However, they should have done some more test runs to make sure their data was solid. The guest statistician said the difference was "statisically insignificant", but that somehow translated to a tiny advantage for the air football when they did their recap/summary.

[doom1701]

I'm not getting the lack of love for the bullet myth. If there weren't people that didn't believe it were actually possible, there wouldn't be people still dying from trying to do it. It's one of those things that, even though in the back of our heads we know the magician is faking it, we wonder "Could it really be done?"

[mportuesi]

If there weren't people that didn't believe it were actually possible, there wouldn't be people still dying from trying to do it.

Okay, I definitely buy this argument. Heck, maybe this episode saved someone's life. And they did definitely bust the myth in the end.

But the experiments they did along the way were pretty weak. Initially, they stuck the bullet between two rows of clenched molar teeth and then hit it with a pendulum. That's a lot more surface area bearing down on the bullet than if they put it up front, between the incisors. So when the bullet held between the simulated teeth, it wasn't a valid result.

Only when they actually shot a bullet into the pig jaw did it become obvious there's no way teeth could catch the bullet. That's what I meant when they were saved from their own bad experiments.

[srs5694]

I watched this, but may have missed a little bit, because I still have a question... why was the acceleration imparted on both the regular and helium balls identical? I would have guessed that the lighter (helium) ball should be sent flying at a faster rate.

At least in part, this is a mass/weight thing. As I and others have stated, the helium-filled balloon weighed less, as measured by the scales, but its mass is another matter. We don't know if its mass was any less than that of the air-filled balloon. As it's mass, not weight, that's in the physics equations that describe this sort of thing, it's mass that's important.

That said, the buoyancy of the helium-filled balloon could conceivably have an effect on the velocity of the ball as it leaves a kicker's foot, but I don't know what effect that might have.

[srs5694]

But the experiments they did along the way were pretty weak. Initially, they stuck the bullet between two rows of clenched molar teeth and then hit it with a pendulum. That's a lot more surface area bearing down on the bullet than if they put it up front, between the incisors. So when the bullet held between the simulated teeth, it wasn't a valid result.

This is true; but if you recall, they did try it the way you suggest. The problem is that the rig ended up destroying the front teeth. As with many of their tests, they basically gave the myth every chance; moving the bullet to the molars would seem to increase the chance of it working, but it failed even with that benefit.

[balboa dave]

In my feeble scientific mind, it should make no difference. Hang Time is a result of two things--the force (or acceleration, to be more accurate) imparted onto the ball, and gravity. They made sure that the acceleration imparted on the ball was the same for both. That means that the ball was travelling at the same speed, no matter what the ball was filled with.

Once the ball is moving, it's just a function of gravity to bring it back down--and gravity "pulls" at the same speed no matter what the weight of the object is. So the ball is going to spend the same time in the air no matter what, as long as it was thrown at the same speed.

The two hiccups are the mass/inertia issue, which could allow a "heavier" ball to fly further, but not attain more hang time (unless the spin does impart lift--wasn't clear on that), and the force that can be imparted by a real kicker or thrower. The throwing machine really wasn't affected by a couple of grams either way, but it's possible a real person could be--causing less force to be imparted onto the "heavier" ball because of both inertia at rest and plain old strength. But I doubt that a couple of grams would matter for an experienced football player, either.A pound of lead may fall at the same speed as a pound of feathers in a vacuum, but not in an atmosphere. Hang time is extremly affected by wind, whether it's trailing, leading, or cross, and lift has everything to do with it. It is just a measure of time in the air, and has nothing to do with distance. A shorter kick could easily have more hang time, and usually does. The entire experiment missed the point.

[mgar]

At least in part, this is a mass/weight thing. As I and others have stated, the helium-filled balloon weighed less, as measured by the scales, but its mass is another matter. We don't know if its mass was any less than that of the air-filled balloon. As it's mass, not weight, that's in the physics equations that describe this sort of thing, it's mass that's important.The mass of the football filled with helium will be less because helium at 13 psi is less dense that air at 13 psi.


That said, the buoyancy of the helium-filled balloon could conceivably have an effect on the velocity of the ball as it leaves a kicker's foot, but I don't know what effect that might have.The buoyancy of the helium filled ball is the same as the air filled ball because the volume of the ball is the same in both cases.

[doom1701]

A pound of lead may fall at the same speed as a pound of feathers in a vacuum, but not in an atmosphere. Hang time is extremly affected by wind, whether it's trailing, leading, or cross, and lift has everything to do with it. It is just a measure of time in the air, and has nothing to do with distance. A shorter kick could easily have more hang time, and usually does. The entire experiment missed the point.

Hang time just boils down to upwards force rather than forward force. Either the ball is going up, or it's going forward (or both). Yeah, the wind can have an affect on it, but not enough to cause a difference between the two footballs. The "hang time" effect that you describe has to do with wind resistance--both of the footballs would have the exact same level of wind resistance, no matter what they are filled with.

[doom1701]

The mass of the football filled with helium will be less because helium at 13 psi is less dense that air at 13 psi.

The buoyancy of the helium filled ball is the same as the air filled ball because the volume of the ball is the same in both cases.

The buoyancy is different because the density is different, isn't it? If I had a lead filled football, it's going to sink, even though the volume of the ball is exactly the same. If the 13psi of helium is truly less dense than the 13psi of air, then the situation is exactly the same--one would be less dense, and hence more buoyant.

Think about it from the perspective a balloon--I don't know what PSI you fill a balloon to, but let's say it's 3PSI. A balloon filled to 3PSI with air will just sit there, while an identical balloon filled to the same PSI and same volume will jump into the air (and pop itself on the ceiling).

[mgar]

The buoyancy is different because the density is different, isn't it? If I had a lead filled football, it's going to sink, even though the volume of the ball is exactly the same. If the 13psi of helium is truly less dense than the 13psi of air, then the situation is exactly the same--one would be less dense, and hence more buoyant.

Think about it from the perspective a balloon--I don't know what PSI you fill a balloon to, but let's say it's 3PSI. A balloon filled to 3PSI with air will just sit there, while an identical balloon filled to the same PSI and same volume will jump into the air (and pop itself on the ceiling).

The buoyancy force is not a function of mass of the object or its contents. The buoyancy force is simply equal to the volume of the object times the mass of the air that it displaces (the air in the room, the atmosphere, etc). A lead ball and a plastic ball will both have the same buoyancy force if they are the same volume.

The reason a helium balloon rises, is the helium balloon has less mass. The vertical force on stationary balloon is equal to the force of gravity minus the buoyancy force. If the buoyancy force is larger than the gravity force, then an object will float. The helium balloon filed to an equal volume compared to an air filled balloon will float not because of increased buoyancy, but because of less mass.

[Jonathan_S]

I did really like the football myth. However, they should have done some more test runs to make sure their data was solid. The guest statistician said the difference was "statisically insignificant", but that somehow translated to a tiny advantage for the air football when they did their recap/summary.I'm pretty sure that the final summary was based on pure physics calculations, and wasn't from their experimental numbers.

They were saying that even though the experiment was a wash (statistically insignificant), when they calculated the distance a football should travel from a given force at two different given masses, the air filled (slightly greater mass) football had about a 1" advantage at 70'. But that wasn't a "real world" number, that was from plugging values into physics formulas.

[mgar]

I'm pretty sure that the final summary was based on pure physics calculations, and wasn't from their experimental numbers.

...


I had the opposite impression. The final summary was based on data. My understanding was that even though the difference in the data was statistically insignificant, that the average distance measured was slightly longer for the air filled ball. This would be an inconclusive result, but busts the myth because the difference is too small to be noticed in a real situation. They didn't mention doing any physics calculations.

[Jonathan_S]

I had the opposite impression. The final summary was based on data. My understanding was that even though the difference in the data was statistically insignificant, that the average distance measured was slightly longer for the air filled ball. This would be an inconclusive result, but busts the myth because the difference is too small to be noticed in a real situation. They didn't mention doing any physics calculations.I believe the wording they used was "calculated it mathematically". However, that gave me the impression (possibly mistaken) that this was more than just recrunching the inconclusive experimental data.

[kbohip]

What about the bullet in the teeth myth? Next week are they going to see if its possible to turn a beautiful assistant into a white tiger? wow they must be out of ideas. And instead of changing the micrsecond timer why didn't they move the table holding the teeth forward to the point where the bullet was at the time of the teeth closing?

I almost skipped through that part of the show it was so stupid. This was definitely not one of the better episodes. I think they're running out of ideas.

[darthrsg]

another ep of buildteam. the show seems split between half jamie and adam and half bulid team. they need to get it together. so far ,this to me at least, is not that great a season. i think they ran out ideas too quick. there are loads of myths to be busted but not on family tv. also they keep giving the result away before they go to break. thats dumb.

[vman41]

The reason a helium balloon rises, is the helium balloon has less mass. The vertical force on stationary balloon is equal to the force of gravity minus the buoyancy force. If the buoyancy force is larger than the gravity force, then an object will float. The helium balloon filed to an equal volume compared to an air filled balloon will float not because of increased buoyancy, but because of less mass.

An interesting side observation about bouyancy: A given volume of helium has twice the mass of the same volume of hydrogen, yet a helium-filled balloon will lift 85% as much as a hydrogen-filled balloon.

[srs5694]

The buoyancy force is not a function of mass of the object or its contents. The buoyancy force is simply equal to the volume of the object times the mass of the air that it displaces (the air in the room, the atmosphere, etc). A lead ball and a plastic ball will both have the same buoyancy force if they are the same volume.

Can you back that up with a reference? It certainly doesn't make any sense to me, at least not as the word is commonly used. To back up my point of view, from http://www.answers.com/topic/buoyancy:


buoy·an·cy (boi'ən-sē, bū'yən-)
n
1. a. The tendency or capacity to remain afloat in a liquid or rise in air or gas.
b. The upward force that a fluid exerts on an object less dense than itself.


This definition (part b, specifically) refers to density, both of the object and of its surroundings. An object that's less dense than its surroundings exerts an upward buoyant force. An object that's more dense than its surroundings doesn't. Depending on the density of the surroundings, a solid plastic ball could be buoyant, whereas a solid lead ball of the same volume might not be, despite the fact that they'd both displace the same volume.

[mgar]

Can you back that up with a reference? It certainly doesn't make any sense to me, at least not as the word is commonly used. To back up my point of view, from http://www.answers.com/topic/buoyancy:

http://hyperphysics.phy-astr.gsu.edu/hbase/pbuoy.html#bcomp

I should have used the term buoyant force instead of buoyancy force, but my description is correct. I understand where the confusion is based on the common usage of the word buoyancy.


This definition (part b, specifically) refers to density, both of the object and of its surroundings. An object that's less dense than its surroundings exerts an upward buoyant force. An object that's more dense than its surroundings doesn't. Depending on the density of the surroundings, a solid plastic ball could be buoyant, whereas a solid lead ball of the same volume might not be, despite the fact that they'd both displace the same volume.

The common definition of buoyancy usually means floating which means the force on the object due to gravity is less than the buoyant force, and the object would be described as buoyant.

Also, the b) part of the definition b. The upward force that a fluid exerts on an object less dense than itself. is not scientifically correct because the buoyant force only depends on the displacement volume and the density of the displaced fluid (liquid or gas). The buoyancy force is not a function of the density of the object, however the net vertical force is.

Also, I did notice one mistake:

I stated that the buoyancy force is the displaced volume times the mass.

It should be the displaced volume time the mass times the acceleration due to gravity.

[srs5694]

http://hyperphysics.phy-astr.gsu.ed...buoy.html#bcomp

I should have used the term buoyant force instead of buoyancy force, but my description is correct. I understand where the confusion is based on the common usage of the word buoyancy.

OK, so this is a case where the scientific definition isn't quite the same as the common definition, which has been causing cross-communication. Knowing that eliminates much of the disagreement on this point in this thread.

[5thcrewman]

Super-fizzy lifting gas!