CHAPTER 13 GASES (Pressure) Date _____________ Force Pressure = due to a force gravitational e/m, strong, weak Area Force = mass acceleration velocity (speed + direction) change in speed magnitude of the force SI unit of force – a Newton: the amount of force needed to move a 1 kg object so that it increases its speed by 1 m/s each second textbook: mass __________ accelerates due to gravity ____________ Force = __________ _________ = _________ N 9.81 m/s2 9.81 m/s2
convert cm2 to m2 start with 100 cm = 1 m then, (100 cm)2 = (1 m)2 adjust this to account for the book not pushing on whole surface of hand… say ½ ?? Pressure due to the book on your hand: convert cm2 to m2 start with 100 cm = 1 m then, (100 cm)2 = (1 m)2 so, 10,000 cm2 = 1 m2
the air pushes in all directions (nearly) uniformly Pressure due to the atmosphere: the push push which way does the air push ? the air pushes in all directions (nearly) uniformly air pushes in all directions not like the weight of an object that only pushes DOWN air pushes in all directions
GRAVITY gravity air pushes in all directions air THE ATMOSPHERE! Measuring air (atmospheric) pressure You might think that the water would fall down and out due to _______________ Why doesn’t the water in the tube fall down and out ? GRAVITY there must be something pushing the water up against the force of _________ What is doing the pushing!? ________________________ gravity GRAVITY air pushes in all directions air THE ATMOSPHERE! the water can’t fall out of the tube, because to fall out of the tube, the level of water in the tray would have to rise, the air pressure is holding the water in the tray down
WEIGHT 760 mm air pushes in all directions the mercury in the tube stops falling when… the pressure due to the weight of the mercury EQUALS the pressure due to the air this will be true when the column of mercury is 760 mm high WEIGHT air pushes in all directions 760 mm intellicast
WEIGHT air pushes in all directions 760 mm
WEIGHT air pushes in all directions (height) 760 mm
pressure due to the air is ______ times greater compare to pressure of the book on your hand pressure due to the air is ______ times greater How can that be? Feel it….
WEIGHT 760 mm air pushes in all directions Standard Atmospheric Pressure the pressure that will support a column of mercury that is exactly 760 mm high 1 standard atmosphere (atm) = 760 mmHg (exactly) = 29.92 inHg (4 SF) = 101,325 Pa (6 SF) OR WEIGHT air pushes in all directions 760 mm
But, mercury is so nasty….link …. why not just fill the tube with water 1. Water freezes at 32F (0C)… that’s a problem in Vermont… 2. …. how high would the column have to be ? …. ??
average atmospheric pressure will support a column of water that is
average atmospheric pressure will support a column of water that is
The Kinetic Theory of Gases…. how does a gas exert pressure and what affects the magnitude of that pressure … 1st…. temperature
the RP of a sample are in a constant state of motion The Kinetic Theory - based in the principle that… __________________________________ the RP of a sample are in a constant state of motion as long as the RP are at a temperature above absolute zero The Kinetic Theory applied to Gases the pressure due to a gas is a consequence of: _________________________________________ as each RP strikes the wall (or you), it bounces back __________________________________________ changed direction, therefore, its velocity changed so, ____________________________ by Newton’s Laws, the RP exerted the _______________________________ collisions of the gas RP with the container walls (or with you) at the same speed (elastic collision) “whack” the RP accelerated a force acted on the RP (the wall pushed on the RP) same force on the container wall