Final answer:
In an air-free chamber, a horizontally thrown pebble and a pebble dropped from the same height will have the same time of fall since gravity affects both equally and the horizontal motion does not influence the vertical descent.
Step-by-step explanation:
The question you've posed pertains to the physics concept of free fall and projectile motion. When comparing the times of fall of two pebbles in an air-free chamber, one thrown horizontally and one dropped from rest from the same height, their time of descent will be the same. This is because the vertical motion is solely influenced by gravity, which acts equally on both pebbles, and is not affected by any horizontal motion or forces. The horizontal motion of the thrown pebble does not influence its falling time due to the constant horizontal velocity after being thrown, and gravity only affects vertical motion.
It's important to note that in practicing ideal physics conditions—no air resistance—the vertical descent is independent of any horizontal velocity. Thus, regardless of one pebble being tossed horizontally, both pebbles will hit the ground simultaneously, assuming they were released at the same time. This is because gravity pulls on both pebbles equally, and the horizontal throw does not add any force in the vertical direction.