Probability Definition. The probability of an event is a number between $0$ to $1$ which measures the chance of that event occurring. The likelihood of the occurrence of the event increases as the probability varies from $0$ to $1$. The probability of the occurrence of an impossible event is $0$ and that of a certain to occur event is $1$.
As altitude increases, air pressure decreases. Gravity causes the atmosphere to become heavier the closer you are to the ground. The atmosphere may seem weightless but all the â¦ air molecules add up to a tremendous amount of mass.
3. Air pressure is the pressure exerted by the weight of air above. Air pressure decreases with an. increase in altitude because there is less air above to exert a downward force as one moves away. from Earthâs surface.4. Cold and dry air is more dense and therefore heavier than warm humid air.. Air pressure is the pressure exerted by the weight of air above. Air pressure decreases with an. increase in altitude because there is less air above to exert a downward force as one moves away. from Earthâs surface.