1. Force = mass x acceleration
Chapter 13 Gases (pressure)
Date:____________
Force
Due to a force … gravitational, strong , e/m….
Pressure =
Area
Force = mass x acceleration
Change in velocity (speed + direction)
SI unit of Force:
The Newton
1 Newton (N) = 1kg ( 1𝑚/𝑠 1𝑠 ) = 1kg m/s2
2kg
Textbook mass ____________
acceleration due to gravity_______________
Force =_________ x_________ = ________
9.8 m/s2
2kg
9.8 m/s2
20 N

2. What pressure does the book exert on your hand?
Let us model the book as a solid pure substance
Pressure =
20 N RP
Area
Pressure =
20 N
= 300 N/m2
(0.20 m ) (0.26 m)
The RP’s of the book, only push down upon your hand
Pretend the book is a pure substance?
How does the air inside of the soccer ball exert a pressure?

3. The RP’s of air are able to move around freely and collide with the inside surfaces of the ball.
The RP’s of the air pushes against the side of the ball in all directions (nearly uniformly)
These collisions create pressure within the confined space of the ball. It is like the particles are pushing out in all directions!
Gases Push in all directions, unlike the weight of an object, which only pushes DOWN

4. Measuring atmospheric pressure
The atmosphere exerts a pressure (push) on all things.
We can measure atmospheric pressure using a barometer
The device is filled with Mercury…. You might expect the mercury to simply fall out of the tube and overflow due to ___________. But it does not!
Gravity
Air pushes in all directions
Gravity
There must be something pushing against the force of gravity…
The mercury can/t fall out of the tube, In order to fall out, the level in the tray would have to rise. The air pressure is holding the mercury in the pool down.

5. The Mercury in the column stops falling, when the pressure due to the weight of the mercury
EQUALS
The pressure due to the atmosphere
This is true when the column of Mercury is 760 mm high
Weight
760 mm
Air pushes in all directions

6. Standard Atmospheric Pressure
A single atmosphere of pressure will support a column of Hg that is exactly 760 mm high.
1 standard atmosphere (atm) = 760 mm Hg
760 mm
Atms and mm of Hg are common ways of recording pressures for gases…
Air pushes in all directions