What would happen if you sneezed in space?

18 March 2014


Sneeze 5



What would happen if you sneezed in space?


Tamela - Actually, that's a funny question because I was thinking of this the other day, having a lunch time chat. But if we're in space, I'm going to assume you're either in the space vehicle or you're in your space suit, you've got your helmet on, I was wondering - I don't actually know the answer, but what if you sneeze when you're on your space suit doing an, an extravehicular walk and suddenly it gets all over your face shield, maybe you need windscreen wipers or something. Richard looks like he knows what might happen.

Chris - That could be bad.

Richard - Well, I was going to tell you, sneezing is very similar. I was talking to actually Chris Hadfield, the Canadian astronaut about sweat in space. He writes about this in his book. So, you're on the treadmill in the International Space Station and as you normally sweat. Well, sweat will normally stay on your skin. In the space station, when you're in this microgravity environment, the sweat literally pings off everywhere.

Tamela - Sure, these little droplets.

Richard - Yeah, these little drops of sweat. You have to keep wiping yourself down. Otherwise - and this is so unpleasant - you zap your crewmates with your sweat. It's equally true with a sneeze. So, if a sneeze has coming out of your nose and heading for one of your crewmates, it will just keep going.

Tamela - So, sort of lethal.

Ginny - Would you also be propelled backwards if you sneeze because with the whole equal and opposite forces, I know that if you say, open a fire extinguisher when you're on a wheelie chair, you get propelled backwards. So, if you sneezed in space, would you start flying off in the other direction?

Chris - Depends where your nose points, doesn't it? I mean, did you normally sneeze with your ... wouldn't you be propelled upwards, Ginny?

Richard - Used as some sort of propulsion system.

Ginny - Yeah, okay. Would you go upwards though?

Richard - I suppose yes is the answer.

Tamela - You'd have to hold on to something.

Richard - You would because it doesn't take much to start moving. The big problem that the astronauts have in space is the stopping. So, if they're moving heavy weights around the space station for instance, they can pick up a heavy weight, no problem at all. And they can start moving with it and then they realise, "Oh no, the bulkhead is coming up. How do I stop?"


Yes, a sneeze directed towards the ground would make you weigh less, partly because you'll have expelled some mucus and partly owing to Newton's 3rd Law: for every action there is an equal and opposite reaction. So you push the sneeze out and, it pushes back on you with an equal and opposite force.

This means that the gas expelled groundwards exerts a small force back on your in the upwards direction. This acceleration momentarily competes with the downwards gravitational acceleration, making you temporarily "weigh" a tiny bit less.

Does a person weigh less when they sneeze downward? Like if they stood on a very sensitive scale, would they momentarily become lighter when they sneezed?

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