This document discusses key concepts relating to pressure in fluids. It defines pressure as force per unit area and discusses hydrostatic pressure, how pressure increases with depth due to gravity. It describes Torricelli's experiment which demonstrated atmospheric pressure and how a vacuum is created. Pascal's principle is introduced, explaining how pressure is transmitted equally in all directions throughout a confined fluid.

1. 4. Pressure in fluids
1. Definition of pressure
2. Hydrostatic pressure. Siphon
3. Atmospheric pressure.
Torricelli experiment
4. Buoyancy
5. Pascal´s law
© Patricio Gómez Lesarri
© science.howstuffworks.com

2. 1. Definition of pressure
Force per unit of area
Concentration of force in a
point
Effect of a force in fluids
Units:
Pascal 1 Pa= 1 N.m-2
kPa, MPa
Atmosphere: 101300 Pa ≈ 100
kPa = 760 mm Hg
Bar 1 Bar= 100 kPa
© http://physics.wfu.edu
P =
F
S
© blogs.wwf.org.uk/

3. 2. Hydrostatic pressure
Why does water not fall ?
https://www.youtube.com/wa
Variables
Height
Liquid density
© www.tutiempo.net

4. 2. Hydrostatic law
Pressure doesn´t depend on
the amount of fluid
https://www.youtube.com/watch?v=J7ymn6f2Bl8
Paradoja de Pascal:
https://www.youtube.com/watch?v=EJHrr21UvY8© http://www.school-for-champions.com/
P = ρ.g.h
P =
mg
S
=
ρVg
S
= ρgh

5. 2. Siphon: communicating vessels
Vasos comunicantes
Sifón
https://www.youtube.com/w
Tubos en U
© fq-experimentos.blogspot.com

6. 2. Siphon misconceptions
© Lewis C. Epstein

7. 2. Siphon misconceptions
© Lewis C. Epstein

8. 2. Pressure misconceptions
© Lewis C. Epstein

9. 2. Pressure misconceptions
© Lewis C. Epstein

10. 3. Lab activity:
Presión hidrostática
Práctica virtual: buzo en el
mar :
http://webs.um.es/gregomc/LabESO/PresionMar/PresionMar.html
© Gregorio J Molina Cuberos
http://webs.um.es/gregomc/LabESO/index.htm

11. 3. Atmospheric pressure.
Torricelli´s experiment
Torricelli´s experiment
https://www.youtube.com/watch?v
https://www.youtube.com/watch?v
https://phet.colorado.edu/es/simul
http://www.kscience.co.uk/animatio
© http://www2.southeastern.edu/
P = ρ.g.h =13700kg.m−3
.9,8m.s−2
.0,76m =101300Pa

12. 3. Vacuum. Pressure difference
Gas occupies its own space
https://www.youtube.com/watch?v=Po1C5qk3pSQ
A net force is applied between
points at different pressures
https://www.youtube.com/
watch?v=_CXd2h5O8OU
https://www.youtube.com/
watch?v=28TIyWdfxxc
https://www.youtube.com/
watch?
v=qXclcimrmfI&index=13
1&list=PLC02CFDE5690E
4010

13. 4. Buoyancy
Does mandarines float?
Variables:
Mass
Fluid density
 Volume
© www.playdoughtoplato.com

14. 4. Archimedes´ principle
https://www.youtube.com
/watch?v=eQsmq3Hu9HA
https://www.youtube.com
/watch?v=VDSYXmvjg6M
Buoyant force applied to an
object equals the weight
of the displaced fluid
© Hila science
FB = ρ.V.g

15. 4. Archimedes misconceptions
© Lewis C. Epstein

16. 4. Archimedes misconceptions
© Lewis C. Epstein

17. 5. Pascal´s principle
The pressure applied to a
fluid is transmited
undiminished to every
point of the fluid and to the
walls of the container
https://www.youtube.com
/watch?
v=iD55ynlUH8g#t=14
https://www.youtube.co
m/watch?
v=8ma4kW3xVT0
© http://www.tutorvista.com

18. 5. Hydraulic jack
Hydraulic system which
allows to multiply forces
according to Pascal´s law
© hyperphysics.phy-astr.gsu.edu
P1 = P2
F1
S1
=
F2
S2