I've lost track of who is arguing what, but I don't think you guys really disagree.
Agreed!
you're both just being a bit sloppy with your terms, especially "acceleration" and "free fall"
Acceleration is a change in an objects speed and/or direction.
That, I'm afraid, is sloppy. Acceleration is the rate of change of velocity with respect to time. dv/dt, in calculus terms. Speed is not the same as velocity. Speed is not a vector term - it has magnitude, but no direction. If you drive a car in a circle, your speed can stay constant, but you are still accelerating - in this case, towards the centre of the circle - as your velocity components are continuously changing.
Weightlessness is the result of free fall. An object is in free fall when the only force acting on it is gravity. (or no force at all in relativity, since gravity is not considered a force). Although an object in orbit changes direction and technically could be considered "accelerating", that "acceleration" is due only to the force of gravity, therefore it is considered in free fall.
An object in orbit is absolutely accelerating - at 9.81 metres per second, per second, towards the centre of the earth. Its speed remains content, but its velocity components are changing, hence the constant change in direction.
An object that is truly accelerating cannot be weightless because changes in direction and/or speed require a force other than gravity be applied because Newton's First Law. An object subject only to gravity will move at a constant speed and in a straight line unless acted upon by another force.
No. The text in bold is fundamentally wrong. An object subject only to gravity will accelerate at a constant rate. On or near our planet, any object will experience a force on it equal to its mass multiplied by the acceleration due to gravity, g. And because F=ma, if the only force on it is 'mg', then mg=ma, so a=g, meaning our object will accelerate at g, or 9.81ms
-2. If it wasn't for air resistance, objects dropped from height would keep getting faster and faster.
Anyway, back to the question that started the whole discussion. A person in a spacecraft will not feel weightless unless the space craft is in freefall. If the flat earth is accelerating at 9.81m/s, the space craft must somehow be accelerating along with it in order to "keep up" and maintain visual contact with the earth. Any person in the spacecraft would have to accelerating along with the spacecraft, will not be in free fall and therefore cannot experience weightlessness.
Agreed - hence my question to Pete and Action80. How could an astronaut feel weightless for months on end if they are constantly at the same altitude above the flat earth? Regardless of FE views on gravity, an object that maintains altitude above the flat earth would have to have some force keeping it there, just like lift in an aircraft, which means the astronauts wouldn't feel weightless.