Air leaking out of a tire My bike was not used for over 7 months, It has no holes on it. Yet I found it empty, is there a specific reason why air leaks out of objects without any "force" acting upon the tire to force the air out? 
 A: Yes, there is a force, because the air pressure inside the tire is larger than the pressure  outside, so air will try to leave from any hole it finds, however small. It might be through some micro cracks on the tire or, more often, through leaks from the air valve. 
A: A gas (like air) will tend to diffuse through any material, and the rate of diffusion will be roughly proportional to the pressure difference between the inside and the outside.  It so happens that it tends to diffuse through the rubber of ordinary bike inner tubes fairly rapidly.  In addition, the inner tube wall is quite thin, and the thinner the material the more rapid the diffusion.
Some bike inner tubes (made thin and of special rubber for "performance") allow diffusion so rapidly that they must be pumped up twice a day.  More typical bike inner tubes allow diffusion at a rate such that you generally should pump up your tires once a week, if high pressure, or at least once a month if low pressure (below roughly 50 psi).
