I think the pressure is caused by both the weight and the collision force.sophiecentaur said:This question is bound to get a lot of people going as both of your alternatives carry some of the truth of the situation. The molecules in the air are all pulled towards the centre of the Earth but do not all fall down because of their thermal motion and the resulting collisions. At the bottom of a column of air (i.e. on the ground) the pressure is die to the adjacent molecules continually hitting the ground. Those molecules, in turn, are collided with by molecules higher up and so on, up tot the edge of the atmosphere ( it would go on for ever, in fact, getting less and less dense in an approximately exponential way). Every molecule in a vertical column will be imposing its weight on the molecules below it so you could say that the pressure is actually caused by the weight of all the molecules overhead. If Earth were cold enough, there would be a 'thin' layer of liquified air all over the surface and the pressure would be easier to appreciate and to calculate but there is no other force available to increase the pressure when it's gaseous so you can say it's still due to weight. Just one caveat and that is that the weight of the molecules at the very limit of the atmosphere is just a bit less (not a lot, of course) than at the surface because they are a couple of hundred km further away.
The "collision force" is there because of the weight. The weight is there because of the gravitational field. If there were no weight, the molecules would just drift off into space so there would be no pressure due to momentum transfer of collisions. Both of the ideas are at work here so it's not an either / or choice.ztdep said:I think the pressure is caused by both the weight and the collision force.
Atmospheric pressure is the weight of the air above a certain point on Earth's surface. It is caused by the force of gravity pulling the air molecules towards the center of the Earth.
Atmospheric pressure is typically measured using a barometer, which measures the force exerted by the weight of the air on a unit of area. The most commonly used unit of measurement for atmospheric pressure is the millibar (mb) or hectopascal (hPa).
The main factors that affect atmospheric pressure include temperature, altitude, and the amount of water vapor in the air. As temperature and altitude increase, atmospheric pressure decreases. Higher levels of water vapor can also result in lower atmospheric pressure.
The Earth's atmosphere is constantly moving due to the rotation of the Earth and the uneven heating of its surface. This movement creates areas of high and low pressure, with air moving from high pressure to low pressure to equalize the pressure imbalances.
Atmospheric pressure plays a crucial role in weather patterns and can have significant impacts on human health. Changes in atmospheric pressure can also affect the behavior of objects, such as causing them to expand or contract.