![]() The center of mass is a single location in an object (or body) on which you can assume gravity acts. That will be more like walking on the moon, and it keeps their breathing volume fairly constant.īut there's another problem, and it has to do with the "center of buoyancy." You might have heard of the "center of mass"-it's like that, but different. One solution to this problem is to just stick the whole human in a pressurized space suit. ![]() When a person inhales, the size of their lungs increases, and this increases the volume of displaced water. Sure, to make sure your test subject survives underwater, you can add a scuba tank so that they can get air-but their breathing is in fact its own problem. To do this, you need to add extra weight to the person.īut there are some problems with this setup. You want them to stand upright on the floor. ![]() Most humans have a weight that's slightly less than the weight of the water they displace, which means they most likely float towards the surface-but you don’t actually want them to do this. You can modify this simulation so that a person could walk on the seafloor as if it was the moon. So if a person takes up a certain volume of water, and the weight of that water is equal to the weight of the person, the net force on them would be zero and they would "float." The magnitude of this upward pushing buoyancy force is equal to the weight of the water displaced-that's called Archimedes’ principle. Instead of a cable pulling up, this upward force is the buoyancy force due to displaced water. The basic idea is once again to have an upward-pushing force to reduce the net downward force. This allows the human to move in all three dimensions-just like they would move on the moon-and practice climbing around on objects like ramps and boxes.Ĭouldn't you just put a person underwater to simulate the moon? Yes, that is one option-but it too has some limitations. The system is able to measure not just the person’s position but also their horizontal speed, and it matches this motion with the suspension point of the cables above them. The tension in the cable is adjusted so that the net downward force (the cable pulling up and gravity pulling down) is the same as the downward-pulling gravitational force on the moon.īut what happens when a person moves? Well, the support point for the cable is some distance above the human and it moves to match the person's motion. This method also uses a cable to pull up on an astronaut-but in this case the person stands on flat ground with the cable pulling them straight up. ![]() NASA calls this the Active Response Gravity Offload System (ARGOS). There's another reduced gravity simulation that's actually quite similar to the pendulum method. This will give me the following plot of position versus time: I'm going to use Tracker Video Analysis and plot the vertical position of the performer in the video in each frame. Let's see if this lever device provides an acceleration similar to that on the moon. Clearly, that's not what would happen on the moon. You can see this in the video: When the performer jumps high enough, the lever is mostly vertical. Instead, this force decreases as the angle increases. Is the vertical acceleration the same as on the moon? This device doesn't provide a constant net force. The device only supports the person at some attachment point, which means they can only walk in a circle and not go wherever they want. But is this really the same as walking on the moon? Well, it's not subjectively the same. If I use a human mass of 75 kilograms, and lever arms of 2.0 and 0.5 meters, then the mass on the end would need to be 250 kilograms.
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