# Zero Gravity: ISS Orbit & Neil Degrasse Tyson

• kghosh
In summary: Weightlessness (or lack of gravity) does cause problems with bone density because the body cannot use the same mechanisms to keep bones strong.
kghosh
I read in a physics textbook that it is not zero gravity in ISS but the fact that the ISS is in "free fall" makes astronauts float around. They do not feel any normal force because the vehicle they are in are also in free fall along with them. Then I watched Neil Degrasse Tyson talk about bone loss in ISS because astronauts are in zero gravity. If it is zero gravity then why is the ISS in orbit? There should be no centripetal force to keep it in orbit. I am confused!

The term 'zero gravity' is often used when referring to things in free fall.

It is inaccurate.

The gravitational force on the Space Station obviously is not zero. It is gravity after all that makes the Space Station orbit the Earth.

The term "zero gravity" does not refer to the force due to gravity. It refers instead to all forces except gravity. When you go to an amusement park and take a ride that bills itself as having a zero g roll, or a zero g drop, gravity is not changing during the course of the ride. Your uneasy stomach tells you that something is changing. That something is your "apparent weight" or "scale weight".

You can't feel the force due to gravity. You can't conduct a local experiment that measures gravity. An example: An accelerometer placed at rest on the surface of the Earth registers an upward acceleration of 9.8 meters/second2. Why? The answer is that the accelerometer does not (and cannot) measure gravity. It measures everything but gravity. In this case, it measures the normal force from the ground that pushes the accelerometer upward. The accelerometer does not sense the downward force from gravitation, so even though the accelerometer is at rest with respect to the Earth it registers an upward acceleration with respect to the Earth.

When NASA and Dr. Tyson speak of the problems such as bone loss due to the zero g environment of space, they are referring to weightlessness (scale weight) rather than gravity.

## 1. What exactly is zero gravity?

Zero gravity, also known as microgravity, is the condition experienced by an object or person when they are in a state of weightlessness. This occurs when the force of gravity is balanced or canceled out by other forces, such as the upward motion of an orbiting spacecraft.

## 2. How does the International Space Station (ISS) maintain its orbit?

The ISS maintains its orbit by constantly falling towards the Earth due to the force of gravity, but also moving forward with enough speed to avoid crashing into the planet. This is known as freefall and is the same principle that allows objects in orbit to experience zero gravity.

## 3. What are some effects of zero gravity on the human body?

The human body experiences a variety of changes in zero gravity, including loss of bone and muscle density, changes in blood flow and circulation, and shifts in bodily fluids. These effects can lead to physical changes and challenges for astronauts during long-term space missions.

## 4. How does Neil Degrasse Tyson relate to zero gravity and the ISS?

Neil Degrasse Tyson is a renowned astrophysicist and science communicator who has been involved in various projects related to the ISS and space exploration. He has given lectures on the science of zero gravity and has also been a vocal advocate for the importance of space exploration and the use of the ISS for scientific research.

## 5. Can anyone experience zero gravity on Earth?

While true zero gravity can only be experienced in space, there are ways to simulate the feeling of weightlessness on Earth. These include parabolic flight, where an aircraft follows a specific trajectory to produce periods of zero gravity, and underwater training facilities that mimic the low gravity environment of space.

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