Confusion of "Over G" and the relevant "Free Body Physics".
Recent posts once again high light the confusion that exists over this topic.
So here is one of my favourite thought exercises for everyone to try.
Scenario:
I take you to the top of a tall building - name your own choice.
The equipment is:
1) You - the "experimental candidate"
2) A tall box which you can stand in - fully enclosed - breathing holes and a door on one tall side. Height of box such that, standing vertically in the box, your head is in contact with the "ceiling" - reasons will become obvious;
3) One tennis ball.
Experimental Method:
I ask you to stand in the box, hand you the tennis ball, close the door of the box, hold it out clear of the roof of the building; AND drop the lot - box, you, tennis ball.
(Qualitative descriptions will do - save the maths and associated assumptions.)
Ignoring air resistance
1) What is the vertical acceleration of the total system - box, you, ball?
2) What force is between the top of the box and your head?
You have nothing to keep you occupied for the immediate future so you throw the tennis ball towards the floor of the box:
3) What is the absolute (i.e. relative to ground) acceleration of the tennis ball whilst you are throwing it downwards but before you release it?
4) What is the absolute acceleration of the tennis ball after it leaves your hand and before it hits the floor of the box?
5) What is the absolute acceleration of the Box whilst you are throwing the ball but before you release it?
6) What is the absolute acceleration of the Box after you release the ball and before it hits the floor?
Next the ball hits the floor and rebounds.
7) Describe what happens to the acceleration of the box at the moment of rebounding - i.e. whilst the ball is compressing then decompressing in rebound.
8) Ditto once the ball has rebounded.
9) Identify any occurrences of "over G"
AND it is directly "on topic" - it addresses the foundation principles of physics supporting the confused issue of "over G" - at WTC7 naturally.
