This is so cool. Honestly I'm always amazed by every physics lesson I'm given. We live in such an interesting place with so many quirks and features, it's like a video game with lots of easter eggs. I wish I would've seen this 6 years ago back when it was first posted
Hi Matt, OK, so the First Rule of Science in the Imagination Station science van is, we don't talk about Science in the Imagination Station science van. I'm sure you know the second rule... -- Carl Nelson, Chief Scientist, Imagination Station.
How does this video only have 100 likes? Are super nerdy engineer types like me a minority? Lol. Great video. Videos like this are a great way to demonstrate science to kids(and non stem field adults). I really enjoyed this. Thanks!
If the helium balloon is moving according to air pressure, is this really Newton’s law of motion or fluid dynamics? Or something else? Proper amateur here haha
@@thatsmeinthepic Newton's law a of motion takes place on the air in the van. once the air "moved" to the back of the car it pushes the baloon to the front.
The helium balloon is not actively seeking less dense air, but simply the more dense air "falls" around it, moving it upwards in the process. In a substance with more uniform density like water, water falls around the object and it floats upwards, unless the object is denser than water and then the virtual seesaw is reversed and it sinks.
That actually is true. For example, if you put a helium balloon inside of a car and you accelerate, the balloon will actually move forward because its mass is lower compared to the mass of the air around it. So, that's kind of how negative mass would act like, because that helium balloon is pretty much negative mass in comparison to the air around it.
I've come up with some questions regarding that: 1. What will happen to the helium balloon if we open the trunk of the car (so no air gradient can form)? will the baloon behave just like the air baloon? 2. Do you need a higher force accelerating an air sealed car (F = m*a) versus a car where the air can move out in the back since you need to accelerate the air (frictionless air)? 3. Do you need less force accelerating a helium filled car (because it is .. lighter)? 4. When I pump my tires with helium, will the resulting lateral capability of the car decrease (because of Upforce from Helium decreasing my Fz on the tire, while this does not happen in the lateral direction 5. Can I increase it with a heavier gas in the tire (more downforce, friction value is constant in this consideration)?
i really want the answer for the first question. like does the whole car be in the low pressure zone and woud it decrease indeffinitely if the car keeps accelerating
Sulfur hexafluoride for drag cars and helium for rally cars? Might be pros and cons to each although not a significant enough benefit to justify it, I assume. I want answers regardless lol
1) There will still be a pressure gradient, because suction will be pulling the internal air mass forward. However, it would be hard to notice because turbulence from swirling air being pulled in from the back would mess up the nice neat experiment. 2) No, because, again, the air mass _is_ accelerating. Otherwise, the interior of the car would become a vacuum after it has left the air behind. 3) Yes, but the effect would be almost immeasurably tiny. 4) Yes, but again, to a very, _very_ tiny effect. It would be much easier, less expensive, and healthier to avoid having desert before you go driving instead. 5) Yes, but it would be much easier to just put some weights in your car.
Wow. I knew this watching with just one balloon. Watching it with 2 balloons with different densities is amazing to compare. I also loved the centripetal acceleration acting on both balloons. PERFECT 🏆🏆🏆🏆🏆
Yes, but what if they baloon was floating mid air, balanced with some light stuff, then car or train starts to move. Not connected via rope, but actually floating.
Great video, excellent explanations. I just have an issue with what was said starting at 02:22, that the helium balloon moves because the air gets compressed at the front or rear of car during accelerations. What I think is actually happening is much simpler: As the car accelerates, the local gravity vector inside the car is no longer vertical. For everything inside the car, "up" and "down" are no longer vertical. For this reason, during accelerations, a pendulum will be suspended from the car's ceiling at the exact same angle as the helium balloon attached to the car's floor. That angle will indicate the local gravity vector direction during the acceleration. The balloon is just trying to point "up" the ame way the pendulum is trying to point "down" - but it is only in the absence of acceleration that those directions are vertical relative to the car.
corisco tupi - you are correct and almost everyone else including the Chief Scientist have it completely wrong. It is all about the equivalence of gravity and acceleration and the new combined direction of the gravity/acceleration force. I have put the explanation in images here: drive.google.com/open?id=1hhJ8AHYYS--331dNtdp07GM9fJovP8ns
@@Reuben-John In your Image 2 with the net gravity pointing to the left, does that result from gravity pointing down and inertia pointing left? Because the acceleration of the vehicle is towards the right.
@@Reuben-John The direction of gravity doesn’t change lol wtf it can’t. Gravity always points toward centre mass no matter what. Even Newton knew that.
I'm going to assume the questions she's asking are because she is representing us, "the viewer" because for a science channel it seems really odd to me that a host of a would otherwise come off like that. Anyways great demo and I just want to add I don't intend for it to sound like I'm trying to burn the host it just seems weird to me.
Air is water, contained water. The closer to the earth the pressure is higher. This is because of the mass of the air above pushing down. The same principle happens in the oceans the lower you go the more mass pushing down creating more pressure. The same applies in the container on all levels.
It’s quite simple really. The acceleration in the car is required to overcome the already established downward vector. As a result of the acceleration, RDD (relative density disequilibrium) is created in the car, where the less dense materials (helium balloon) move towards the direction of the motion/acceleration and the more dense materials (humans) move away plum/vertical to the motion. We can recreate this RDD in ANY direction using acceleration. Earth is moving up folks, hence the already established downward vector. Backed by practical references, as per above. RDD ceases to be when an object is free fall.
It does. At 45 degrees latitude, a plumb bob points about 1/2 degree away from the centre of the earth. The helium baloon points opposite the plumb bob.
There is a better explanation for the motion of the balloon. The balloon is reacting to its relative acceleration versus the car's relative deceleration. Not so much the change in air density of the air inside the car. That air density shift would take time to develop significantly. The balloon responds instantaneously. The buoyancy force is always opposite gravity. But gravity is just acceleration. When you decelerate the car, it is as if you accelerate the balloon relative to the car. An instantaneous forward acceleration just as is experienced by the air filled balloon relative to the car. The helium balloon now has a horizontal forward acceleration relative to the car in addition to a downward acceleration due to gravity. Add those two acceleration vectors & the resultant "apparent" accel vector is down and forward. The buoyancy force on the balloon is greater and opposite to this new resultant, i.e. up & backward is the buoyancy vector. If you measured pressure in the car I believe you would see little change and not instantly during the quick stop. There would some but not much.
Hey Bandidojr, unfortunately no hot Cheetos, earlier in the day I was doing a demo with some food coloring. That stuff is hard to get off your fingers! --Carl
According to the science guy, seems as is he is saying there is a point at which if you are inside an enclosed vehicle at the very front of it, if the acceleration is high enough, it would actually dimish air (oxygen) and you would be gasping for air. It would become less dense (thinner). This is why pilots use oxygen at high altitudes or in fighter jets because of the heights at which they need to operate and also due to the high acceleration the aircaft go through during certain maneuvers. With this type of oxygen pressure differential or lack of and without support equipment, your brain could not handle it and you would pass out and many pilots do because of this. By the same token, if you put people (we are filled not only with air but also with water and other heavier than air components in our bodies, but for the sake of simple explanation, let's just say analagous to the balloon filled with air (Same density or pehaps slightly heavier if the balloon was filled by mouth, there will be moisture which will make the balloon a bit heavier), denser than air. Water remains on ground, because it is denser than air, by this proven logic, things heavier than air fall to the ground while things lighter than air float (rise up). It is that simple based on "AIR" density, no scientific neutonian mumbo jumbo called "gravity". We are also filled with air/water, as mentioned, and if we put people inside an airbus in high decent (High acceleration) the people would float upwards, analogous to the ballon filled with regular air moving back along with the high pressure. This has been seen many times in videos of how NASA mimics astronauts out in space when they are more likely inside a high decent high acceleration air bus. It takes a bit of thinking to understand this. Some get it right away and some people don't. Once you know that anything lighter than air, wether by volume (balloon filled with helium, or hot air) or by force (airfoil wing in high speed genereates pressure differential forces) rises because at the top of the wing the pressure is less than at the bottom, underneath the pressure is higher, the logic is clear. Imagine this, as if you were lifting an object, if you put equal pressure with your fingers on top and bottom, the object sits steady, does not go anywhere. However, if you put higher pressure under it and lower the pressure at the top the object will rise or tends to go near the low pressure side. It is interesting how Neuton is defined: Sir Isaac Newton, was an English mathematician and physicist who lived from 1642-1727. The legend is that Newton discovered Gravity when he saw a falling apple while thinking about the forces of nature. GRAVITY IS A LEGEND! meaning not a fact. An apple falls by the simple fact that is is an object heavier than air. PERIOD!. Water seeks its own horizon and not curvison and bottom line, things that are lighter than AIR, rise up while things that are heavier than AIR fall or remain grounded. Hot ballons rise up because you are removing the moisture from the air inside the ballon, thus making it lighter than the air outside. Makes sense? The "Key Reference" here is not Gravity but "AIR density". Denser air means more moisture particles in the air, thus heaveir air. For example: A full size prop driven aircraft has trouble in low density, air that has no moisture or little moisture, since the prop needs to grab onto something to be able to be effective. If the propeller has nothing to grab unto in air then the airplane thrust is less effective, Look up Density Altitute. Every good pilot is aware and understand this, althouh this can get a bit confusing when talking about things that rise up by nature of making them lighter than air. In the latter instance, the propeller actually needs to grab onto thicker air so that it can speed up the air flowing over the wing (airfoil) and create the pressure differential required for the top of the wing to be lighter than the bottom pressure, so that the airplane rises up. You will never be able to measure gravity, it is a nebulous term, created by a 33 degree mason placed into society to remove God from the equation amongst many similar instances to remove the One thing that has given man natural senses that if we learn to rely more on logic with a bit of honest scientific repeateable and proven guidelines, we can answer many questions without the mumbo jumbo.
Fun experiment but as usual the wrong explanation. It has nothing to do with air pressure. What is actually happening is that the direction of the overall force of gravity is changing with the acceleration and deceleration of the car. When the car accelerates its the same as gravity shifting towards the rear of the car - just like a car going up a hill - so the helium balloon should lean forward as you would expect with a car climbing a hill at constant speed. This is Einstein's equivalence of gravity and acceleration theory in action. Full explanation here: drive.google.com/drive/folders/1hhJ8AHYYS--331dNtdp07GM9fJovP8ns?usp=sharing
If you could do this experiment in a vacuum (with rubber that doesn't burst) both balloons would roll on the floor, both forward when it brakes, both backward when it accelerates. You need the air to have a slanted pressure gradient resulting from the combination of both accelerations to create the uplift for the buoyant balloon. Which, of course, also results from all masses being pulled down obliquely.
The only reason the balloon cares about the direction of gravity is _because_ of the pressure gradient it creates. You are correct that acceleration is the same as shifting the direction of gravity, but if those were the only forces present, the balloon would fall to the bottom of the van and then be pushed _backwards_ by the acceleration. Gravity creates a pressure gradient, shifting the direction of gravity shifts the direction of the gradient, and the balloon follows the gradient.
This is so cool. Honestly I'm always amazed by every physics lesson I'm given. We live in such an interesting place with so many quirks and features, it's like a video game with lots of easter eggs. I wish I would've seen this 6 years ago back when it was first posted
4:05 "This is the first time everybody survived." How many people have you lost in previous attempts????? 😂😂😂
Hi Matt,
OK, so the First Rule of Science in the Imagination Station science van is, we don't talk about Science in the Imagination Station science van.
I'm sure you know the second rule...
-- Carl Nelson, Chief Scientist, Imagination Station.
Imagination Station science van isn't a fight club, is it ?
Carl, you aren't Tyler, r u ? xD
Always love these segments, keep them coming!
How does this video only have 100 likes? Are super nerdy engineer types like me a minority? Lol. Great video. Videos like this are a great way to demonstrate science to kids(and non stem field adults). I really enjoyed this. Thanks!
Ikr epic video rlly helped me clear my concepts
If the helium balloon is moving according to air pressure, is this really Newton’s law of motion or fluid dynamics? Or something else? Proper amateur here haha
@@thatsmeinthepic Newton's law a of motion takes place on the air in the van. once the air "moved" to the back of the car it pushes the baloon to the front.
Probably because it's fairly obvious as soon as you think about it for like 3 seconds, if you're actually scientifically-inclined.
Maybe because the explanation is completely WRONG? It has nothing to do with air compressibility...😢
I look forward to more videos.Keep it up!
The helium balloon is not actively seeking less dense air, but simply the more dense air "falls" around it, moving it upwards in the process. In a substance with more uniform density like water, water falls around the object and it floats upwards, unless the object is denser than water and then the virtual seesaw is reversed and it sinks.
"so we were never actually moving then?" XD
😆😆
GREAT Demonstration
That was pretty cool. I'm over 50 and have been a bit of an under-educated nerd most of my adult life. But I have never seen this before.
Never knew about the helium Ballon case until now.
Honestly I had never even thought about this!
This was very cool! Thank you very much for this expoination!
exactly the case of normal balloon was in my finals question paper this video helped me, seen this 6-7 years ago when it was aired in tv
That actually is true. For example, if you put a helium balloon inside of a car and you accelerate, the balloon will actually move forward because its mass is lower compared to the mass of the air around it. So, that's kind of how negative mass would act like, because that helium balloon is pretty much negative mass in comparison to the air around it.
1:48 is where it happens if you don't want to hear them bickering for two minutes.
What will happen if the gas in the balloon has density equal to that of air( and the balloon is massless)?
If the balloon doesn't move wrt an outside observer, the van would accelerate relative to it, but I'm not sure if that would be the case.
in that case bouyant force will not be applied and it should not move
I've come up with some questions regarding that:
1. What will happen to the helium balloon if we open the trunk of the car (so no air gradient can form)? will the baloon behave just like the air baloon?
2. Do you need a higher force accelerating an air sealed car (F = m*a) versus a car where the air can move out in the back since you need to accelerate the air (frictionless air)?
3. Do you need less force accelerating a helium filled car (because it is .. lighter)?
4. When I pump my tires with helium, will the resulting lateral capability of the car decrease (because of Upforce from Helium decreasing my Fz on the tire, while this does not happen in the lateral direction
5. Can I increase it with a heavier gas in the tire (more downforce, friction value is constant in this consideration)?
i really want the answer for the first question. like does the whole car be in the low pressure zone and woud it decrease indeffinitely if the car keeps accelerating
Sulfur hexafluoride for drag cars and helium for rally cars? Might be pros and cons to each although not a significant enough benefit to justify it, I assume. I want answers regardless lol
1) There will still be a pressure gradient, because suction will be pulling the internal air mass forward. However, it would be hard to notice because turbulence from swirling air being pulled in from the back would mess up the nice neat experiment.
2) No, because, again, the air mass _is_ accelerating. Otherwise, the interior of the car would become a vacuum after it has left the air behind.
3) Yes, but the effect would be almost immeasurably tiny.
4) Yes, but again, to a very, _very_ tiny effect. It would be much easier, less expensive, and healthier to avoid having desert before you go driving instead.
5) Yes, but it would be much easier to just put some weights in your car.
1:02 huh, so we were never moving! 😂😂😂😂😂😂😂
😄😄
Woman moment
@@demitrivavaroutsos4141 ?
@@kwewee what do you not understand bud?
@@demitrivavaroutsos4141 wdym woman moment
Wow. I knew this watching with just one balloon. Watching it with 2 balloons with different densities is amazing to compare. I also loved the centripetal acceleration acting on both balloons. PERFECT 🏆🏆🏆🏆🏆
What is the helium balloon was tied outisde?
What would happen if some windows were open?
Air resistence would throw everything backwards
I was moved in an instant! I stopped being an inertial observer to be an otherwise non-inertial one.
Wow 😲😲😲😲😲❤️❤️
Yes, but what if they baloon was floating mid air, balanced with some light stuff, then car or train starts to move. Not connected via rope, but actually floating.
Great video, excellent explanations. I just have an issue with what was said starting at 02:22, that the helium balloon moves because the air gets compressed at the front or rear of car during accelerations. What I think is actually happening is much simpler: As the car accelerates, the local gravity vector inside the car is no longer vertical. For everything inside the car, "up" and "down" are no longer vertical. For this reason, during accelerations, a pendulum will be suspended from the car's ceiling at the exact same angle as the helium balloon attached to the car's floor. That angle will indicate the local gravity vector direction during the acceleration. The balloon is just trying to point "up" the ame way the pendulum is trying to point "down" - but it is only in the absence of acceleration that those directions are vertical relative to the car.
corisco tupi are you dumb...... i bet you 5 million dolars if you do this experiment in vaccum the balloon's gonna act like any other object
+Pradipta Sen
If you had 5 million dollars to bet, you'd be that much poorer. Go back to school and relearn the basics, son.
corisco tupi - you are correct and almost everyone else including the Chief Scientist have it completely wrong. It is all about the equivalence of gravity and acceleration and the new combined direction of the gravity/acceleration force. I have put the explanation in images here: drive.google.com/open?id=1hhJ8AHYYS--331dNtdp07GM9fJovP8ns
@@Reuben-John In your Image 2 with the net gravity pointing to the left, does that result from gravity pointing down and inertia pointing left? Because the acceleration of the vehicle is towards the right.
@@Reuben-John The direction of gravity doesn’t change lol wtf it can’t. Gravity always points toward centre mass no matter what. Even Newton knew that.
I'm going to assume the questions she's asking are because she is representing us, "the viewer" because for a science channel it seems really odd to me that a host of a would otherwise come off like that. Anyways great demo and I just want to add I don't intend for it to sound like I'm trying to burn the host it just seems weird to me.
awesome share
got the passenger seat out of the road !
Now try it in a back hole!
*are dey helium balloons?*
My physics sir saleem ahmed given activity to think about it am fascinated to see this BRILLIANT EXPLANATION ❤❤
Air is water, contained water. The closer to the earth the pressure is higher.
This is because of the mass of the air above pushing down.
The same principle happens in the oceans the lower you go the more mass pushing down creating more pressure. The same applies in the container on all levels.
Water also has all the weight of the air molecules.
Everything is a fluid
Thank you so much for this video, this video clarifies a very huge 🧩🧩 puzzle.
Except that there are only bodies in motion and nothing is really at rest...
tell that to water
The balloon isn’t moving back though is it. It’s staying still…
It’s quite simple really. The acceleration in the car is required to overcome the already established downward vector. As a result of the acceleration, RDD (relative density disequilibrium) is created in the car, where the less dense materials (helium balloon) move towards the direction of the motion/acceleration and the more dense materials (humans) move away plum/vertical to the motion. We can recreate this RDD in ANY direction using acceleration.
Earth is moving up folks, hence the already established downward vector. Backed by practical references, as per above. RDD ceases to be when an object is free fall.
"Huh."
Try one that's a mix of helium and air at neutral buoyancy.
Now do the trick but find the heliums ballons buoyancy get it to float in the middle of the van and watch it NOT MOVE?....
What wrong with his thumb?
earth is moving right why don't the balloon act like that out side ?
It does. At 45 degrees latitude, a plumb bob points about 1/2 degree away from the centre of the earth. The helium baloon points opposite the plumb bob.
are dey helium balloons
Wanna know how to make a normal air balloon behave like a helium balloon?
Yeah
Put it in water.
Why do globies think inertia applies to spinning objects? Try this with a car going in a continuous circle.
There is a better explanation for the motion of the balloon. The balloon is reacting to its relative acceleration versus the car's relative deceleration. Not so much the change in air density of the air inside the car. That air density shift would take time to develop significantly. The balloon responds instantaneously.
The buoyancy force is always opposite gravity. But gravity is just acceleration. When you decelerate the car, it is as if you accelerate the balloon relative to the car. An instantaneous forward acceleration just as is experienced by the air filled balloon relative to the car. The helium balloon now has a horizontal forward acceleration relative to the car in addition to a downward acceleration due to gravity. Add those two acceleration vectors & the resultant "apparent" accel vector is down and forward. The buoyancy force on the balloon is greater and opposite to this new resultant, i.e. up & backward is the buoyancy vector.
If you measured pressure in the car I believe you would see little change and not instantly during the quick stop. There would some but not much.
My mind is blown
Thanks for break checking me :(
Omg. My question 20 years ago for why the fly I'm watchiny kept with our car's speed when i was bored.
Genius
cool
Was he eating hot cheetos?
Hey Bandidojr, unfortunately no hot Cheetos, earlier in the day I was doing a demo with some food coloring. That stuff is hard to get off your fingers!
--Carl
She sounds like Dee from its always sunny
Adi adash
33
Wowwwww
Rosa hari....
"Never before attempted"...By you. There are videos on this from eleven years ago....8 years prior to this video.
Huh
According to the science guy, seems as is he is saying there is a point at which if you are inside an enclosed vehicle at the very front of it, if the acceleration is high enough, it would actually dimish air (oxygen) and you would be gasping for air. It would become less dense (thinner). This is why pilots use oxygen at high altitudes or in fighter jets because of the heights at which they need to operate and also due to the high acceleration the aircaft go through during certain maneuvers. With this type of oxygen pressure differential or lack of and without support equipment, your brain could not handle it and you would pass out and many pilots do because of this.
By the same token, if you put people (we are filled not only with air but also with water and other heavier than air components in our bodies, but for the sake of simple explanation, let's just say analagous to the balloon filled with air (Same density or pehaps slightly heavier if the balloon was filled by mouth, there will be moisture which will make the balloon a bit heavier), denser than air. Water remains on ground, because it is denser than air, by this proven logic, things heavier than air fall to the ground while things lighter than air float (rise up). It is that simple based on "AIR" density, no scientific neutonian mumbo jumbo called "gravity".
We are also filled with air/water, as mentioned, and if we put people inside an airbus in high decent (High acceleration) the people would float upwards, analogous to the ballon filled with regular air moving back along with the high pressure. This has been seen many times in videos of how NASA mimics astronauts out in space when they are more likely inside a high decent high acceleration air bus. It takes a bit of thinking to understand this. Some get it right away and some people don't.
Once you know that anything lighter than air, wether by volume (balloon filled with helium, or hot air) or by force (airfoil wing in high speed genereates pressure differential forces) rises because at the top of the wing the pressure is less than at the bottom, underneath the pressure is higher, the logic is clear. Imagine this, as if you were lifting an object, if you put equal pressure with your fingers on top and bottom, the object sits steady, does not go anywhere. However, if you put higher pressure under it and lower the pressure at the top the object will rise or tends to go near the low pressure side.
It is interesting how Neuton is defined: Sir Isaac Newton, was an English mathematician and physicist who lived from 1642-1727. The legend is that Newton discovered Gravity when he saw a falling apple while thinking about the forces of nature. GRAVITY IS A LEGEND! meaning not a fact. An apple falls by the simple fact
that is is an object heavier than air. PERIOD!.
Water seeks its own horizon and not curvison and bottom line, things that are lighter than AIR, rise up while things that are heavier than AIR fall or remain grounded.
Hot ballons rise up because you are removing the moisture from the air inside the ballon, thus making it lighter than the air outside. Makes sense?
The "Key Reference" here is not Gravity but "AIR density". Denser air means more moisture particles in the air, thus heaveir air.
For example: A full size prop driven aircraft has trouble in low density, air that has no moisture or little moisture, since the prop needs to grab onto something to be able to be effective. If the propeller has nothing to grab unto in air then the airplane thrust is less effective, Look up Density Altitute. Every good pilot is aware and understand this, althouh this can get a bit confusing when talking about things that rise up by nature of making them lighter than air. In the latter instance, the propeller actually needs to grab onto thicker air so that it can speed up the air flowing over the wing (airfoil) and create the pressure differential required for the top of the wing to be lighter than the bottom pressure, so that the airplane rises up.
You will never be able to measure gravity, it is a nebulous term, created by a 33 degree mason placed into society to remove God from the equation amongst many similar instances to remove the One thing that has given man natural senses that if we learn to rely more on logic with a bit of honest scientific repeateable and proven guidelines, we can answer many questions without the mumbo jumbo.
Your failure to understand science, doesn't mean it's not true.
We can, and have measured gravity, your denial of such facts doesn't change anything.
@mia micro-FLIGHT
I cant believe how stupid you are...
This guy is flat earther 100%
@@GoldSrc_ no one understands what causes gravity.
You might believe you understand but you don't, if you did you would have yourself a Nobel Prize
I don't think she gets it
Now we play with drones. 😂😂
Any students from CU..??
Huah!
Non intuitive
So... the Earth is always moving up?
women: hUH
haha nice comment
They are both on a string, of course they will move that way. Do it without a string and let a balloon go. I bet ya wont.
Fun experiment but as usual the wrong explanation. It has nothing to do with air pressure. What is actually happening is that the direction of the overall force of gravity is changing with the acceleration and deceleration of the car. When the car accelerates its the same as gravity shifting towards the rear of the car - just like a car going up a hill - so the helium balloon should lean forward as you would expect with a car climbing a hill at constant speed. This is Einstein's equivalence of gravity and acceleration theory in action. Full explanation here: drive.google.com/drive/folders/1hhJ8AHYYS--331dNtdp07GM9fJovP8ns?usp=sharing
John Nebauer but like...the density of helium being less than the surrounding air is why is moved in the opposite direction.
If you could do this experiment in a vacuum (with rubber that doesn't burst) both balloons would roll on the floor, both forward when it brakes, both backward when it accelerates. You need the air to have a slanted pressure gradient resulting from the combination of both accelerations to create the uplift for the buoyant balloon. Which, of course, also results from all masses being pulled down obliquely.
@@djboo7779 No Density is not a force. Nor an acceleration. That's what matters. Density is just a property of mass.
Great explanation btw John. 👌
The only reason the balloon cares about the direction of gravity is _because_ of the pressure gradient it creates. You are correct that acceleration is the same as shifting the direction of gravity, but if those were the only forces present, the balloon would fall to the bottom of the van and then be pushed _backwards_ by the acceleration. Gravity creates a pressure gradient, shifting the direction of gravity shifts the direction of the gradient, and the balloon follows the gradient.
cool