In absence of air resistance, an object going up or down experience only gravitational pull of Earth. Object undergoes free fall – downwards acceleration of 10 $m / s^{2}$. This means that, in the absence of air resistance, ALL objects falls at the same rate on Earth. Don’t believe me? Check out the video below: (Skip to 1.25 min mark for the “with air resistance” part and 2.50 min mark for the “absence of air resistance” (vacuum) part.)
With air resistance, there will be a drag force acting opposite to direction of motion.
- Drag force increases with speed. Object will eventually reach terminal velocity, where drag force equals gravitational force.
Older NASA video about the “ALL objects falls at the same rate in the absence of air resistance part”:
