[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:08.77,Default,,0000,0000,0000,,(Machine translation by DeepL translate)We've been experimenting with gravity that is 10 times stronger than the Earth's (=10G).
Dialogue: 0,0:00:09.50,0:00:16.43,Default,,0000,0000,0000,,I wonder how much gravity we can actually withstand.
Dialogue: 0,0:00:16.97,0:00:21.87,Default,,0000,0000,0000,,Gravity (strong)
Dialogue: 0,0:00:21.87,0:00:25.86,Default,,0000,0000,0000,,Gravity (Stronger)
Dialogue: 0,0:00:31.63,0:00:37.90,Default,,0000,0000,0000,,First, let's examine the strength of bones.
Dialogue: 0,0:00:40.47,0:00:45.97,Default,,0000,0000,0000,,Let's assume that the entire body weight is supported by a single leg.
Dialogue: 0,0:00:46.92,0:00:53.15,Default,,0000,0000,0000,,The tibia bone has a cross-sectional area of 1 cm2 and can withstand up to 1730 kg.
Dialogue: 0,0:00:56.05,0:01:02.32,Default,,0000,0000,0000,,Even if the gravity increases 10 times, the bone will not break.
Dialogue: 0,0:01:04.23,0:01:11.23,Default,,0000,0000,0000,,If the gravity becomes strong enough for a 50kg person to reach 4680kg
Dialogue: 0,0:01:11.83,0:01:19.07,Default,,0000,0000,0000,,In other words, if gravity becomes 94G, your shins will shatter under your own weight.
Dialogue: 0,0:01:24.50,0:01:30.50,Default,,0000,0000,0000,,This is for a stationary person.
Dialogue: 0,0:01:31.90,0:01:37.90,Default,,0000,0000,0000,,But if you run, the stress on your bones will only be doubled at most
Dialogue: 0,0:01:39.19,0:01:46.63,Default,,0000,0000,0000,,If you don't get knocked down, the problem is weakness of the muscles, not fractures.
Dialogue: 0,0:01:48.33,0:01:55.10,Default,,0000,0000,0000,,Let's think about standing up from a sitting position.
Dialogue: 0,0:01:56.27,0:02:04.60,Default,,0000,0000,0000,,You use your knee joint as a fulcrum to lift yourself up with your quadriceps muscles.
Dialogue: 0,0:02:05.37,0:02:18.27,Default,,0000,0000,0000,,The magnitude of the torque "r1×F" (×2) must be greater than the torque "r2×Mg" that gravity pulls the body to stand.
Dialogue: 0,0:02:18.96,0:02:28.36,Default,,0000,0000,0000,,If we substitute the average value, gravity must be less than 1.1G
Dialogue: 0,0:02:29.20,0:02:35.80,Default,,0000,0000,0000,,In other words, the earth's gravity is the limit for standing by muscle strength alone.
Dialogue: 0,0:02:43.23,0:02:49.57,Default,,0000,0000,0000,,Force F is proportional to the cross-sectional area of the muscle, so if you stand up at 10G
Dialogue: 0,0:02:51.43,0:02:58.10,Default,,0000,0000,0000,,the cross-sectional area must be at least 9 times larger.
Dialogue: 0,0:03:07.87,0:03:17.60,Default,,0000,0000,0000,,In reality, you can't train that much, and even a top athlete can only lift four times the weight of an average person in a squat
Dialogue: 0,0:03:18.73,0:03:26.97,Default,,0000,0000,0000,,Also, if we take into account the fact that you have to bend over, and if the gravity you can withstand is increased by 20%.
Dialogue: 0,0:03:28.00,0:03:35.50,Default,,0000,0000,0000,,Realistically, the limit for a trained person to stand up would be 5.3G.
Dialogue: 0,0:03:36.67,0:03:42.70,Default,,0000,0000,0000,,Next is the limit of gravity when walking.
Dialogue: 0,0:03:43.70,0:03:53.10,Default,,0000,0000,0000,,Let's consider the following model of walking
Dialogue: 0,0:03:53.73,0:04:01.47,Default,,0000,0000,0000,,An inverted pendulum moves forward with the feet as its fulcrum.
Dialogue: 0,0:04:03.43,0:04:11.60,Default,,0000,0000,0000,,The center of gravity moves up and down. The pendulum moves efficiently by exchanging kinetic energy and potential energy.
Dialogue: 0,0:04:13.47,0:04:21.80,Default,,0000,0000,0000,,Here, we refer to the world record of a powerful Icelandic man (179 kg). He can walk 5 steps with a 649kg log on his back.
Dialogue: 0,0:04:22.67,0:04:31.60,Default,,0000,0000,0000,,This is the limit of a person's strength, calculated by a walking model.
Dialogue: 0,0:04:32.53,0:04:42.70,Default,,0000,0000,0000,,When you don't carry a log, you know what the limit of gravity is.
Dialogue: 0,0:04:43.67,0:04:56.03,Default,,0000,0000,0000,,If you increase the gravity, you will not be able to walk at 4.6G
Dialogue: 0,0:04:56.83,0:05:04.27,Default,,0000,0000,0000,,Reference: The world record for weightlifting 62kg class shows that 4.0G is the limit.
Dialogue: 0,0:05:04.27,0:05:13.97,Default,,0000,0000,0000,,The limits of humanity as we know it
Dialogue: 0,0:05:14.93,0:05:23.13,Default,,0000,0000,0000,,Other than that, it is said that if you exceed the 5G experienced by fighter pilots, you will faint because not enough blood can be pumped to your head.
Dialogue: 0,0:05:24.57,0:05:33.07,Default,,0000,0000,0000,,"If we assume that it is safe to go below 5G", then out of the 594 exoplanets with known gravitational acceleration, 
Dialogue: 0,0:05:34.19,0:05:44.39,Default,,0000,0000,0000,,469 planets seem to be safe for human bones and muscles. But some planets will break your bones when you arrive.