This isn't home work, just a curiousity question and I'm obviously under qualified to find the answer. Looking to approximate how the amount of of vacuum in inches of Hg negate the affects of atmospheric pressure in regards to acceleration. We all remember when David Scott let loose the hammer and feather. Let's say we have a quantitive amount of vacuum pressure, how may we approximate the rate of gravitational acceleration on objects with known mass? For example: Given a particle with a mass of 35 lbs/ft3 (or 721 kg/m3). Happens to be coal ash. What is the given approach to gravity (acceleration) at 10(-1) in/hg of vacuum. 10(-2).....10(-3). My goal is to approximate the percentage of gain per inch of Hg on particles of low density. Please, the more rudimentary your answer the better lol.