Astronaut Chris Hadfield recorded a fantastic version of David Bowie’s Space Oddity while circling the Earth in the International Space Station. While I like the music and the views of the Earth from space, this video got me thinking about a very common mistake that people make when they see videos of objects or people floating inside the space station. This is the notion that this happens because there is no gravity. The confusion is further exacerbated because this situation is often referred to as “zero g.” In today’s blog we will see why this is not the case.
To understand what is going on in space let’s do a thought experiment. Imagine that you are standing on top of a high diving platform holding a pencil. As you jump from the platform you let go of the pencil and for a few seconds before you hit the water the pencil will appear to “float” next to you. Is the pencil in this situation experiencing no gravity? Of course not, the pencil is falling alongside you. Now consider this. Suppose in the instant you jump and let go of the pencil a room magically materializes around you in such a way that you are not in contact with any of its surfaces. This room is falling at the same speed you and the pencil are falling, but the room has a camera in a corner pointed towards you. During those few seconds before the room and you hit the water, the camera will record you and the pencil apparently floating in the middle of the room. An observer who watches the camera footage of those few seconds migt conclude that you and the pencil are floating impervious to gravity, but this is not true: you are falling.
This situation is identical to what you see in the video of Chris’s guitar spinning in space and him floating next to it. Chris and his guitar inside the International Space Station are no more floating or impervious to gravity than you and the pencil would be inside that hypothetical room. The reason astronauts appear to float is that (as in the example of the room) they are falling towards the Earth along with the space station around them.
But if this is true, why doesn’t the space station crash and burn?
The reason is that even though it is falling towards Earth, the space station is moving at the right speed parallel to Earth’s surface. If the surface of the Earth were flat the space station would eventually hit the ground. However, because the Earth is round it curves as the station falls, and the speed of the station is carefully controlled to maintain this balance. As a result of this the space station maintains a roughly constant distance from the Earth’s surface even though it is falling towards it.
“Here am I floating
round my tin can
Far above the Moon
Planet Earth is blue
And there's nothing left to do.”
So you see, in the realm of the space station gravity is alive and well. Contrary to the song’s lyrics, the space station and its singing astronaut are not “floating,” they are falling towards Earth, but their speed and direction is such that they never reach the ground.
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To understand what is going on in space let’s do a thought experiment. Imagine that you are standing on top of a high diving platform holding a pencil. As you jump from the platform you let go of the pencil and for a few seconds before you hit the water the pencil will appear to “float” next to you. Is the pencil in this situation experiencing no gravity? Of course not, the pencil is falling alongside you. Now consider this. Suppose in the instant you jump and let go of the pencil a room magically materializes around you in such a way that you are not in contact with any of its surfaces. This room is falling at the same speed you and the pencil are falling, but the room has a camera in a corner pointed towards you. During those few seconds before the room and you hit the water, the camera will record you and the pencil apparently floating in the middle of the room. An observer who watches the camera footage of those few seconds migt conclude that you and the pencil are floating impervious to gravity, but this is not true: you are falling.
This situation is identical to what you see in the video of Chris’s guitar spinning in space and him floating next to it. Chris and his guitar inside the International Space Station are no more floating or impervious to gravity than you and the pencil would be inside that hypothetical room. The reason astronauts appear to float is that (as in the example of the room) they are falling towards the Earth along with the space station around them.
But if this is true, why doesn’t the space station crash and burn?
The reason is that even though it is falling towards Earth, the space station is moving at the right speed parallel to Earth’s surface. If the surface of the Earth were flat the space station would eventually hit the ground. However, because the Earth is round it curves as the station falls, and the speed of the station is carefully controlled to maintain this balance. As a result of this the space station maintains a roughly constant distance from the Earth’s surface even though it is falling towards it.
“Here am I floating
round my tin can
Far above the Moon
Planet Earth is blue
And there's nothing left to do.”
So you see, in the realm of the space station gravity is alive and well. Contrary to the song’s lyrics, the space station and its singing astronaut are not “floating,” they are falling towards Earth, but their speed and direction is such that they never reach the ground.
***
If you like this blog you can have links to new blog posts delivered to your e-mail address. Please click here.
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