We’ve seen footage of astronauts floating around the International Space Station playing Ping Pong with water balls and Pac-Man with strings of M&Ms For a moment, as we watch these astronauts thriving in an environment completely alien to us, we are able to imagine ourselves floating with them
Is the magical experience of weightlessness really limited to the small proportion of human beings who call themselves algonauts (you know, astronauts, cosmonauts, taikonauts, spacenauts)?
Weightlessness might just be for astronauts, but with the help of private companies like SpaceX, Blue Origin and Virgin Galactic, becoming an astronaut might not be so far-fetched
This attractive force, more commonly known as gravity, is a non-contact force that acts on us from a distance
As the name implies, a non-contact force is one that acts between two objects that are not in physical contact with each other, meaning that we don’t need to touch the Earth for gravity to act on us
In fact, we don’t feel the force of gravity unless there is some opposing contact force to counteract it
This opposing force is called the normal force, which, in contrast to gravity, is a contact force acting on physically associated objects
For example, when we are on the ground, the force of Earth’s gravity pulls our body towards the ground
However, because our feet are in physical contact with the ground, there is also a normal force pushing our feet upwards (Figure 1A)
It is through this contact (or normal) force on our feet that we are able to perceive the force of gravity as weight
If the ground under our feet disappeared, gravity would still be acting on us, but we would be unable to feel it
Astronauts feel light when there is nothing to oppose the force of gravity
(A) An astronaut standing on Earth does not feel weightless because the ground creates a normal force that opposes the force of gravity
(B) An astronaut orbiting Earth feels weightless because there is no ground or normal force to counteract the force of gravity
However, because the astronaut is also moving super fast, he continuously falls around the Earth instead of crashing into the Earth
Why do astronauts feel weightless?
In space, astronauts and their spacecraft still have mass and are still subject to Earth’s gravity
In that sense, they still have weight, even though the Earth’s gravitational pull is less in orbit than on Earth’s surface (Box 1)
In essence, the ground has disappeared from under them and both the astronauts and the spacecraft are falling (Figure 1B)
Yes Free fall is defined as “any motion of a body where gravity is the only force acting on it” In the vacuum of space, where there are no air molecules or supporting surfaces, astronauts are influenced only by gravity
Thus, they are falling towards Earth in the acceleration of gravity
Although gravity pulls the astronauts towards Earth, the spacecraft is traveling so quickly in the forward direction that it ends up orbiting around Earth in a circular pattern, much like a ball swinging on the end of a string
For example, the International Space Station is traveling at around 17,150 miles per hour, and that forward momentum keeps astronauts in orbit despite being pulled toward Earth
Well, the easiest and perhaps cheapest way to experience weightlessness is to take advantage of the parabolic flight (also known as a trip aboard the Vomit Comet)
To understand how flying in parabolic arcs creates the feeling of weightlessness, we first need to review the four basic forces that act on an airplane (Figure 2A)
The first force is drag, caused by air molecules that obstruct the plane’s forward motion
To create the feeling of weightlessness, the pilot equates thrust to drag and eliminates lift
At that point, the only unbalanced force acting on the plane is the weight, so the plane and its passengers are in free fall
Then, the plane experiences 20 to 30 seconds of free fall as it completes the climb and begins to fall back to Earth
The resulting parabolic flight path gives the pilot enough time and distance to land safely (Figure 2B)
Parabolic flights allow passengers to experience weightlessness without actually going into space
(A) The four forces acting on an airplane are weight, lift, thrust, and drag
Because acceleration is in the direction of an unbalanced force, airplanes accelerate in the forward direction when thrust is greater than drag and increase in altitude when lift is greater than weight
(B) When the pilot equates thrust to drag and eliminates lift, the only unbalanced force acting on the airplane is weight
Consequently, the plane crashes and passengers feel weightless for about 20-30 seconds
To prevent the plane from crashing into the ground, this weightless maneuver is preceded by a controlled climb and followed by a controlled descent
This cycle of controlled ascent, weightlessness, and controlled descent creates the parabolic flight path characteristic of zero-gravity experiments
As the elevator accelerates towards the 10th floor, passengers feel heavier than usual (airplane climbing to 30,000 feet)
As the elevator approaches floor 10 and immediately changes direction to return to floor 1, passengers feel weightless (free fall maneuver)
Finally, as the elevator slows down upon returning to floor 1, passengers feel heavier than usual (airplane descending at 20,000 feet)
While a trip on the Vomit Comet will give you the feeling of weightlessness, it won’t earn you the name of an astronaut
Although SpaceX is on the cusp of being the first private company to send people into space, its customers are currently limited to NASA astronauts, a wealthy individual named Yusaku Maezawa, and 6-8 of Maezawa’s artistic friends
Thankfully, Blue Origin and Virgin Galactic have provided their weightless experiences for those with slightly smaller checkbooks and slightly less ambitious space travel plans
Paying customers will leave Earth’s atmosphere, see Earth’s curvature, and experience a few minutes of weightlessness before safely returning to the ground
To learn more about the effects of weightlessness on astronauts, check out this Spacecom article
To learn more about experiments carried out aboard the International Space Station, including those looking at the effects of long-term weightlessness on human health, visit this page
To learn how NASA studies the effects of weightlessness on non-living things, visit this site