Pressure and Buoyancy 8th grade Science

1. Pressure Notes
The fun never stops...

2. Pressure in a Fluid
• Liquids and Gases can exert
forces.
– Examples: waves crashing, wind

3. Pressure in a Fluid
• Liquids and Gases can exert
forces.
– Examples: waves crashing, wind
• Liquids and Gases are fluids

4. Pressure in a Fluid
• Liquids and Gases can exert
forces.
– Examples: waves crashing, wind
• Liquids and Gases are fluids
• Fluids exert force

5. Pressure in a Fluid (cont)
Objects in a fluid
experience a buoyant
force resulting from
the pressure exerted
by the fluid.

6. Pressure in a Fluid (cont)
Objects in a fluid
experience a buoyant
force because of the
pressure of the fluid.

7. What is Pressure?
• Pressure is the force per unit
of area applied on the surface
of an object.

8. What is Pressure?
• Pressure is the force per unit
of area applied on the surface
of an object.
• Pressure depends on the force
applied, and the area of contact
over which the force is applied.

9. Calculating Pressure
1 Pa = 1 N/m2
1 Pa is equal to the force of 1 Newton
applied over an area of 1 m 2

10. Pressure and Fluid Height
• For any fluid, pressure depends
only on the height of the column
of fluid above the surface.

11. Pressure and Fluid Height
• For any fluid, pressure depends
only on the height of the column
of fluid above the surface.
• Increasing the height of the
column of fluid increases the
pressure.

12. Pressure and Depth
• Pressure increases
with depth.

13. Pressure and Depth
• Pressure increases
with depth.
• The water column
pushing down
becomes taller and
heavier with increasing
depth.

14. Pressure in All Directions
• Fluids exert a pressure in all directions
on an object.
• The pressure is perpendicular to the
surface of the object.

15. Atmospheric Pressure
• Atmospheric pressure is the force
exerted per unit area by air particles.
• Atmospheric pressure decreases as
elevation increases.

16. Atmospheric Pressure
Crushing things:
• http://www.youtube.com/watch?v=L2WDF1lu
• http://www.youtube.com/watch?v
=gG5YmkmfCpA
• http://www.youtube.com/watch?v
=Uy-SN5j1ogk
• http://www.youtube.com/watch?v
=2WJVHtF8GwI

18. Buoyant Force
Buoyant force is the upward force on
an object in a fluid exerted by the
surrounding fluid.

19. Buoyant Force (cont)
• Buoyant force is the result of
increasing pressure at increasing
depth.
• Pressure on the top of the object is
less than the pressure on the bottom
of the object, resulting in an
unbalanced force.

20. Buoyant Force and Depth
• The pressure exerted by a fluid
increases as depth increases.
• The buoyant force remains constant
on a submerged object.

21. Archimedes Principle
• Archimedes’ principle, the buoyant
force on an object is equal to the
weight of the fluid the object
displaces.
• The buoyant force
does not depend
on the object’s
density or weight.

23. Sinking and Floating
• If the upward
buoyant force is
less than the
object’s weight,
the net force on
the object is
downward.

24. How Can Metal Ships Float?
• Overall density of the ship is less
than the density of water because a
large volume of the ship is filled
with air.

25. Floating and Sinking in the
Atmosphere
• Air produces a buoyant force.
• Helium balloon’s weight is less than
the buoyant force.
• The density of the
balloon is less than
the density of the
surrounding air.

26. Floating and Sinking in the
Atmosphere
• Hot-air balloons float when their weight is less
than the weight of displaced air.
• Heat from the burner heats the air particles
and causes them to move farther apart.
• The density of the balloon
decreases and becomes
less dense than the
surrounding air.

27. Videos
•
•
Mythbusters "Let's Talk Buoyancy"
http://science.howstuffworks.com/6540-mythbusters-lets-talkbuoyancy-video.htm
•
•
Mythbusters Lead balloon 5 min
http://www.youtube.com/watch?v=HZSkM-QEeUg
•
•
Mythbusters Barrel of Bricks
http://www.youtube.com/watch?v=Vt230Pd1oSo
•
•
Sulfur Hexafluoride Gas Boat float
http://www.youtube.com/watch?v=ckaJs_u2U_A
•
•
Mythbusters Sulfur Hexafluoride Boat float attempt
http://www.youtube.com/watch?v=KReTvW7BTHQ