The weight of our rear ends pressed firmly into our seats brings us crashing back to planet Earth, back to reality. Is the magical experience of weightlessness really limited to the tiny proportion of human beings who get to call themselves something-nauts you know, astronauts, cosmonauts, taikonauts, spationauts?
Not so fast. Weightlessness may only be for astronauts, but with the help of private companies like SpaceX, Blue Origin, and Virgin Galactic, becoming astronauts may not be so far-fetched.
Our dreams of floating in space are closer to becoming reality than ever before. Our weight on Earth depends on our mass, which is how much matter we are made of, as well as the force of attraction between our mass and the mass of planet Earth.
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 one another, meaning that we need not be touching Earth for gravity to be acting upon us. In fact, we do not feel the force of gravity unless there is some opposing contact force to counteract it. This opposing force is termed normal force, which in contrast to gravity, is a contact force that acts upon objects that are physically associated with one another.
However, because our feet are in physical contact with the ground, there is also a normal force pushing upwards on our feet 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 beneath our feet were to disappear, gravity would nonetheless be acting upon us, but we would be unable to sense it. This inability to feel gravity would make us feel weightless at least for a moment; Box 1.
So what does this mean for orbiting astronauts? However, they do not feel their weight because nothing is pushing back on them. In essence, the ground has disappeared from beneath them, and both the astronauts and spaceship are falling Figure 1B. Wait, so weightlessness is just free fall?
Thus, they are falling towards Earth at the acceleration of gravity. Although gravity pulls astronauts towards Earth, the spaceship is traveling so quickly in the forward direction that it ends up orbiting around the earth in a circular pattern, much like a ball swinging at the end of a string.
For example, the International Space Station is traveling at about 17, miles per hour , and this forward momentum keeps the astronauts in orbit despite being pulled towards Earth. So how can we actually experience weightlessness? Well, the easiest and perhaps cheapest way to experience weightlessness is to take advantage of parabolic flight aka a trip aboard the Vomit Comet.
To understand how flying in parabolic arcs creates the sensation of weightlessness, we first need to review the four basic forces that act on an airplane Figure 2A. The first force is drag, which is caused by air molecules that obstruct forward movement of the airplane. The second force is thrust, which is a propulsive force supplied by the engine.
The third force is weight. The final force is lift, which results primarily from interactions between the airplane wings and air molecules, and depends on the density of air, the shape of the wings, and the orientation of the airplane in the air. The combination of these four forces determines the speed and direction of the airplane.
To create the sensation of weightlessness, the pilot sets thrust equal to drag and eliminates lift. At this point, the only unbalanced force acting on the plane is weight, so the plane and its passengers are in free fall.
This is what creates the zero-g experience. However, airplanes can only fall so far before they hit the ground. So, prior to this maneuver, the pilot aims the plane upward and applies a burst of thrust.
Then, the plane experiences seconds of free fall as it completes the climb and starts to fall back toward Earth. Finally, once the plane returns to the same altitude it started from on the front half of the arc, the pilot re-engages lift to return the aircraft to a stable altitude and prepare for the next climb. You have already liked this page, you can only like it once!
Imagination versus fact Science and Language 10 Tips for living in weightlessness Science and Language Floating in water Science and Sport Experience weightlessness Science You know a lot about being weightless now, don't you? Check it out! Quiz You know a lot about being weightless now, don't you? Like Thank you for liking You have already liked this page, you can only like it once!
Focus on. Imagination versus fact Science and Language. Floating in water Science and Sport. I am getting off track here. Doesn't this expression say that the gravitational force gets weaker as you get farther from the Earth? But not by has much as you think. A typical height for an orbiting Space Shuttle is about km above the surface of the Earth.
Suppose I have a 75 kg astronaut. What would be the weight gravitational force on the astronaut both on the surface and in orbit? The only difference will be the distance between the astronaut and the center of the Earth. Enough to call it "weightless"? So, this isn't the correct explanation for "weightlessness". You can probably find some examples of why this isn't the cause of "weightlessness".
Here is one that I like. Basically, it is a demonstration of how a suction cup works. I made a video of a mass hanging from a suction dart inside a vacuum bell.
When the air is removed, two things happen. First, the suction cup no longer sucks because they don't really suck anyway. Second, the mass falls. Even though there is essentially no air in the chamber, the mass still falls. Another example is the moon. There is no air on the moon, but astronauts don't float away - even when they jump. Here is John Young's "jump salute". And what about the Earth itself? Why does it orbit the Sun? It orbits because there is a gravitational force between the two objects.
There is an interaction even though there is no air between them. Maybe I should talk about how you feel weight. What is your apparent weight? Let me go ahead and say that what you are feeling right now isn't really gravity. Suppose I start with some examples. Example 1: Go stand in an elevator. Do not push the buttons. Just stand there so that the elevator is at rest. How do you feel? Here is a diagram. Since you are at rest and staying at rest, you are in equilibrium acceleration is zero.
If your acceleration is zero, the net force must also be zero technically, the zero vector. The two forces on you are the force from the floor pushing up and gravitational interaction with the Earth pulling down. The magnitudes of these two forces have to be equal in order for the net force to be zero. Example 2: Now push the "up" button. During the short interval that the elevator accelerates upwards, how do you feel? Or maybe you feel a tad bit heavier. If your elevator is like the one in this building, you might feel frustrated at how slow the damn thing goes.
And what's that funny smell? Here is a diagram for the upward accelerating elevator and you. In terms of forces, what has to be different? If the person is accelerating upwards, the net force must also be upwards. Using the same two forces as above, there are two ways this can happen. Since the gravitational force depends on your mass, the Earth's mass and the distance between those, it doesn't change. This means that the floor must push harder on you.
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