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.
    Actually, quite the opposite. The pressure drops as one increases elevation. For example, at 40000 ft, the elevation a plane might fly, the Pambient will be 18.7 â¦ 5 kPa, much lower than what is seen at sea level (101 kpa or one atm).he pressure drops as one increases elevation. For example, at 40000 ft, the elevation a plane might fly, the Pambient will be 18.7 â¦ 5 kPa, much lower than what is seen at sea level (101 kpa or one atm).