The document discusses pressure and how it is calculated using force and surface area. It provides examples of calculating pressure exerted by the human body and explores how pressure can be increased by decreasing surface area or increasing force. The document also examines evidence of air pressure through demonstrations and explores how air pressure is not easily noticed but can be strong.

1. Understanding Pressure
How much force are you
exerting on the Earth?

2. To answer the question, consider the
following formula: Calculating the actual force you
exert on the ground:
Pressure = Force/ Density
Pascal = 1 N/1m2
where Force (F) = Mass (m) x Acceleration (a)
For example,
with Force expressed in Newtons (N).
Pascal = 534 N/0.11 m2
where Density = Area in m2 = 4,854 N/ m2
Step 1: Finding the Force
a. Multiple your mass (in kg) by 9.8m/s/s (the gravity constant)
b. The answer represents your force in Newton.
Step 2: Finding the Area.
a. On a sheet of graphing paper, trace an outline of your foot.
b. Count the number of squares covered by your foot (4 squares = 1 cm2).
c. Multiple the number of squares by 2 to represent both feet.
d. To convert to m2 , divide the number by 10,000.

3. Force and surface area
• Force = Mass (in kg) x gravity (9.8m/s/s)
• Surface area
– 4 squares = 1 cm2
– Count how many groups of 4 you have
– Divide this number by 10,000 to get from cm2 to
m2
– Multiply this number by 2 to get SA for both feet

4. Buildings should be
designed for a
distributed load of
11,500N/m2 and a
point load of 11,400
N/m2
What could possibly happen to the floor if your
calculated “pressure” is greater than the
designed load limit?

5. If all 1.5 billion people in China
jumped at the same time would
the earth be thrown out of its
orbit?

6. China has a population of about: 1,330,044,544 (July 2008 est.)
Average weight 86.6kg (based on US figures)
Basically the rough estimate for the weight of all those Chinese people comes out to
around 115,181,857,510.4kg. That's a pretty large amount of weight.
However the weight of the earth is approximately
6,000,000,000,000,000,000,000,000 (6E+24) kilograms; which is a
significant difference. On top of all of that take into account the fact that the ground will
compress absorbing a large portion of the force from the jumping, the total
displacement would be negligible.
It is a cute idea; but even with all of those people nothing much would happen. In fact
even if we got everyone in the world to join in (some 6.7+ billion) that total mass is
still extremely insignificant when compared to the weight of the world and not to
mention trying to overcome the inertia of an object that large!
Source(s):
https://www.cia.gov/library/publications…
http://en.wikipedia.org/wiki/Human_weigh…
http://science.howstuffworks.com/questio…

8. Exploring
Pressure

9. PRESSURE
• “press” = push on a surface
• Pressure = Force/ surface area
P= F/ SA
• Unit: pascal (Pa) =1 N/m2

10. Changing pressure
• Do a push up with whole hands vs. finger-
tips
– Which one feels harder?
– What did we change- force or surface area?
– Whole foot versus tip-toes
• With backpack

11. Changing pressure
• Decrease surface area  more pressure
– Tippy toes
– Can you think of opposite?
• Increase force more pressure

12. So Many Units!!!
http://www.sensorsone.co.uk/pressure-units-conversion.html
UNITS EXAMPLES
PSI (pounds per square inch) Pumps for balls, tires
mmHg (Millimeter of Mercury) Blood pressure, the weather
Bar and Atm (atmosphere) Scuba diving
Surface (1 atm) 101,000 Pa
10 meters below (2 atm) 202,000 Pa
Tires 32 psi 220, 500 Pa

13. Air Pressure
• Why is air pressure hard to
notice?
• When are times we do notice air
pressure?

14. Activity 1: Activity 2:
Observations: Observations:
Explanation: Explanation:
Activity 3: Activity 4:
Observations: Observations:
Explanation: Explanation:

15. Evidence for Air Pressure
• Properties of Air
1. Cup and paper towel demo
• Predict- what will happen to the paper towel
when you submerge the cup in water?
• Why is the paper towel able to stay dry?

16. Evidence for Air Pressure
Air takes up space
(has volume)

17. Evidence for Air Pressure
• Properties of Air
2. Empty vs. full balloon
• Predict how the full balloon’s mass will
compare to the empty balloon

18. Evidence for Air Pressure
• Properties of Air
Empty vs. full balloon
• Full balloon is heavier
Air has mass
•1 m3 of air = 1 kg
•In palm, weight of air = force of washing
machine (why don’t we feel it?)

19. Movement of Air Pressure
3. Syringes
–Describe the movement of air
pressure
–How strong is air pressure?

20. Evidence for Air Pressure
• Properties of Air
4. Balloon lift demo
• Air can exert pressure
– See how much you can lift
• Can you think of other ways to demonstrate
that air takes up space and exerts pressure?
• http://www.youtube.com/watch?v=08ezkSrQ5lc&feature=related

21. Air Pressure
• Air Pressure is a
measure of the force of
the air pressing on any
surface