Balloon Buoyancy - What makes balloons float? - By MITK12Videos
Transcript
| 00:11 | Hi there , how's it hanging or should I say | |
| 00:14 | ? How's it floating ? Speaking of floating , why | |
| 00:17 | does this balloon float ? Helium balloons float ? Because | |
| 00:20 | the density of medium this lesson that's here because they're | |
| 00:23 | lighter than air because helium is less dense than air | |
| 00:27 | . I'm hearing a trend in the answer , but | |
| 00:29 | there's one more question . What exactly is the force | |
| 00:31 | acting on the balloon ? I actually don't know . | |
| 00:34 | Mm that stuff . I'm not sure . The buoyancy | |
| 00:37 | force , bingo . The buoyancy force . The same | |
| 00:40 | force responsible for keeping boats from sinking ducky's from drowning | |
| 00:45 | . But how exactly does buoyancy cause helium balloons to | |
| 00:48 | move upward ? Let's head over to the physics department | |
| 00:51 | at MIT to do a little experimentation . To find | |
| 00:54 | out . Here we are with the Technical services group | |
| 01:01 | at MIT . They've picked out a demo that's going | |
| 01:03 | to help us find the answer to our buoyancy question | |
| 01:06 | . Now , check in your brain because this is | |
| 01:09 | what you need to know about the setup and then | |
| 01:11 | guess what ? You can try it at home . | |
| 01:14 | This is dan , a gentleman of TsG . He | |
| 01:17 | has placed two balloons in a box . One balloon | |
| 01:20 | is filled with air and is hanging from the top | |
| 01:22 | of the box . The other is filled with helium | |
| 01:24 | and is taped to the bottom of the box . | |
| 01:26 | The box is loosely closed and therefore filled with air | |
| 01:30 | dan is going to give the box to push and | |
| 01:32 | we'll see which way the balloons will move inside the | |
| 01:34 | box . Will they move backwards or forwards ? Let's | |
| 01:38 | see . Did you see it ? Watch again ? | |
| 01:42 | The balloon filled with air hangs back while the balloon | |
| 01:46 | filled with helium appears to spring forward . How will | |
| 01:50 | we ever explain this with science ? Let's take a | |
| 01:54 | look back at the setup . The helium balloon moved | |
| 01:56 | forward while the air balloon fell back first . Let's | |
| 02:00 | explain the hanging balloons behavior . It hangs back just | |
| 02:03 | as you do when you're sitting in a car . | |
| 02:05 | Accelerating forward . You feel like you're pushed back in | |
| 02:08 | your seat because really your body wants to stay where | |
| 02:10 | it was . Similarly , the hanging balloon wants to | |
| 02:13 | stay in place as the box moves forward so it | |
| 02:16 | appears to fall backwards in the box . Now , | |
| 02:20 | for the helium balloon , maybe the closed box makes | |
| 02:24 | the difference . Let's take a closer look at the | |
| 02:27 | air particles in the box before the push , the | |
| 02:29 | air is equally distributed and the pressure caused by air | |
| 02:32 | particles bumping into each other is the same throughout the | |
| 02:35 | box as the box is pushed forward , the air | |
| 02:37 | particles just like the air filled balloon are left behind | |
| 02:41 | and gather at the back of the box . Now | |
| 02:43 | we have a pressure imbalance , There is higher pressure | |
| 02:46 | and more air particles bumping into each other at the | |
| 02:49 | back of the box than at the front . Ah | |
| 02:51 | ha ! There are more air molecules bumping into the | |
| 02:54 | balloon from the back than from the front . So | |
| 02:57 | the high pressure in the back must push the helium | |
| 03:00 | balloon forward . And that's the motion we see . | |
| 03:03 | Now . We can look at why balloons float up | |
| 03:05 | into the sky when a balloon rises up in the | |
| 03:07 | atmosphere , it must also be moving away from high | |
| 03:10 | pressure air to low pressure air that sounds right up | |
| 03:13 | at high altitudes . The air is much thinner because | |
| 03:16 | it's at a lower pressure than at sea level . | |
| 03:18 | This is why hikers often bring oxygen to the top | |
| 03:21 | of Mount Everest because the air at the summit is | |
| 03:23 | so thin . The air pressure difference is drastic from | |
| 03:27 | sea level to the summit of Mount Everest . But | |
| 03:30 | what about along the length of a balloon ? Since | |
| 03:33 | it or not ? The differences there . The slight | |
| 03:35 | miniscule change and pressure from below the balloon to above | |
| 03:38 | . It is enough to overcome the downward force of | |
| 03:41 | gravity cause a net upward push on the balloon and | |
| 03:44 | Walla . We have found our missing force , and | |
| 03:49 | there you have it . The poignancy can be neutral | |
| 03:52 | and keep things in one place like are floating canoe | |
| 03:55 | and our duck , but it can also be responsible | |
| 03:57 | for the acceleration or overwhelming push on one side of | |
| 04:01 | an object , causing it to move . Mhm . |
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