1. The problem statement, all variables and given/known data We have an alpha particle moving in the air (p=10^5 Pa). Its range is "d". What would be the range if the pressure was q=10 Pa only. 2. Relevant equations x=d*(p/q) ??? 3. The attempt at a solution I think the particle is slowed down the more the more is the number of molecules in the air. And the number of molecules is proportional to the pressures (from the ideal gas law). It seems to be too easy that the range will be incresed by the quotient of the pressures.