CHAPTER 13 GASES Pressure Pressure Date Force Area

CHAPTER 13 GASES (Pressure) Pressure = Date _______ Force Area Force = mass acceleration e of d u t i n mag rce o f e h t ce r o f to a tional ak due e a t w i v , gra strong e/m, change in speed velocity (speed + direction) 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 _____ 9. 81 m/s 2 accelerates due to gravity ______ 9. 81 m/s 2 = _____ N Force = _____

Pressure due to the book on your hand: adjust this to account for the book not pushing on whole surface of hand… say ½ ? ? convert cm 2 to m 2 start with 100 cm = 1 m then, (100 cm)2 = (1 m)2 so, 10, 000 cm 2 = 1 m 2

Pressure due to the atmosphere: air pushes in all directions the push which way does the air push ? 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

Measuring air (atmospheric) pressure You might think that the water would fall down and out due to ________ GRAVITY Why doesn’t the water in the tube fall down and out ? GRAVITY air pushes in all directions there must be something pushing the water up against the force of _____ gravity What is doing the pushing!? THE ATMOSPHERE! ____________ the water can’t fall out air 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

air pushes in all directions WEIGHT 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 760 mm intellicast

WEIGHT air pushes in all directions 760 mm

WEIGHT (height) 760 mm air pushes in all directions

compare to pressure of the book on your hand pressure due to the air is ______ times greater How can that be? Feel it….

Standard Atmospheric Pressure the pressure that will support a column of mercury that is exactly 760 mm high WEIGHT 1 standard atmosphere (atm) = 760 mm. Hg (exactly) OR 760 mm air pushes in all directions = 29. 92 in. Hg (4 SF) = 101, 325 Pa (6 SF)

But, mercury is so nasty…. link …. why not just fill the tube with water 1. Water freezes at 32 F (0 C)… that’s a problem in Vermont… 2. …. how high would the column have to be ? …. ? ?

re u s s e r cp i r e h p er s t o a m w t f a o e n g a m r u l e o v c a a t r o p p will su that is

re u s s e r cp i r e h p er s t o a m w t f a o e n g a m r u l e o v c a a t r o p p will su that is

The Kinetic Theory of Gases…. how does a gas exert pressure and what affects the magnitude of that pressure … 1 st…. temperature

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: collisions of the gas RP with the container walls _____________________ (or with you) k” ac h w “ as each RP strikes the wall (or you), it bounces back _____________________ at the same speed (elastic collision) changed direction, therefore, its velocity changed so, ______________ the RP accelerated so, ______________ a force acted on the RP (the wall pushed on the RP) by Newton’s Laws, the RP exerted the ________________ same force on the container wall