Normalforcelessness

= Normalforcelessness =

In free fall, gravity does still act on a falling mass, but it is not balanced by the normal force. No apparent weight is felt because nothing opposes the mass's tendency to fall (put a scale under your feet and it falls with you). The mass accelerates with calculable gravitational acceleration (about 9.8 m/s^2 near the Earth's surface).

Astronauts in orbit are affected by the force of gravity nearly as much as on the Earth's surface: at an elevation of 100 km above the Earth's surface, gravitational acceleration is about 9.4 m/s^2.

However, without the normal force, the astronaut feels "weightless". The word associated with this term does not accurately describe the situation however. What is missing is the "normal force", that which holds him or her against the direction of the gravitational force, which is towards the center of the Earth.

Hence, an appropriate term for this situation is "normalforcelessness". Normal force is the force that is measured by a spring scale and is usually called apparent weight. In normalforcelessness the apparent weight is zero.

Some physicists define weight not as the force of gravity, but as the scale measurement. In this case, normal force and weight are the same. The term normalforcelessness only applies if weight is defined as the force of gravity on an object (which is the prevailing, but not uniform, view).

References

* Hewitt, Paul, 2002. "Conceptual Physics". Addison-Wesley.
* Halliday, Resnick, Walker, 2001. "Fundamentals of Physics". Wiley.
* Serway, Faughn, 2006. "College Physics". Thomson (Brooks-Cole).