Unit 6, Lesson 2 - Pressure Lesson Outline: 1. Scalars and Vectors 2. Pressure

1. PressureUnit SIX, Lesson 6.2
By Margielene D. Judan

2. LESSON OUTLINE
Scalars andVectors
Pressure

3. Various quantities in nature can be:
• Scalar quantity – magnitude only
• Vector quantity – magnitude + direction

4. Various quantities in nature can be:
• Examples:
1. 20 mL – it tells you the volume of the water. Does it have a
direction? No. It is a scalar.
2. 100℃ - it tells you the temperature. Does it have a
direction? No. It is a scalar.
3. 30 m/s – it tells you the speed. Does it have a direction?
No. It is a scalar.

5. Various quantities in nature can be:
• Examples:
4. 40 m/s N of E – it tells you the velocity of an object. Does it
have a direction? Yes. It says that an object moves 40
meters per second north of east. Thus, it is a vector.
5. 10 N – it tells you the force of an object. Does it have a
direction? Yes. Forces have always a direction. It may be a
push (forward), pull (backward), etc. It is a vector.

7. Distance vs. Displacement
• “A man walks 100 meters.” That is a
distance. It doesn’t have a direction. It
is a scalar.
• “A man walks 100 meters forward.” That
is a displacement. It has a direction. It
is a vector.

8. Distance vs. Displacement
• Also, displacement is the straight-line
distance from point A to B.

9. Distance vs. Displacement
• For example, John walks 100 m east and 30 m north on his
way to school. What arrow represents the displacement?
100m east
30m north
A
B
C

10. Distance vs. Displacement
• Answer: C.
• Displacement is the distance from point of origin to point of
destination and vice-versa.
100m east
30m north
A
B
C

11. Speed vs. Velocity
• 20 m/s is a speed. It doesn’t have a direction. It is a scalar.
• 20 m/s 10° east is a velocity. It has a direction, east. It is a
vector.

12. Today we will study a very important scalar
quantity known as pressure.

13. Pressure
• Force over an area.
• SI unit is pascal (Pa), named
after French mathematician
Blaise Pascal
• Another unit is N/m2.
•P =
𝐹
𝐴
P = pressure F = force
A = area

14. Pressure
• If P =
𝐹
𝐴
• F = PA
•A =
𝐹
𝑃

15. Pressure
• Calculate the pressure in pascals (Pa) if an object exerts a
force of 100 N in an area of 10m2.
P = F/A
P = (100 N)/(10m2)
P = 10 Pa (10 N/m2 could also be used)

16. Pressure (Try This!)
• Calculate the pressure in pascals (Pa) if an object exerts a
force of 20 N in an area of 5m2.
P = F/A
P = (20 N)/(5m2)
P = 4 Pa

17. Pressure (Try This!)
• Calculate the area of a box if it exerts a force of 20 N and
pressure of 10 Pa.
A = F/P
A = (20 N)/(10 Pa)
A = 2 m2

18. Pressure (Try This!)
• Calculate the force of a fingernail if it exerts a pressure of
1000 Pa and its area is 0.01m2.
F = PA
F = (1000 Pa)(0.01m2)
F = 10 N

19. Pressure
• Using the formula P =
𝐹
𝐴
, we can see the following
relationships:
P is directly proportional with F (numerator).
P is inversely proportional with A (denominator).

20. Pressure
P is directly proportional with F (numerator).
P is inversely proportional with A (denominator).
• If force increases, pressure also increases.
• If force decreases, pressure also decreases.
• If area increases, pressure decreases.
• If area decreases, pressure increases.

21. Pressure
Which would you prefer to press, the left or right?

22. Pressure
Of course, the right! It
would be painful to
press the left.
That’s because the less
the area, the greater the
pressure.
The greater the area,
the less the pressure.
less area
larger area

23. Pressure
Of course, the right! It would be painful to press the left.

24. Pressure
High heels can also do damage to some floors because the
heels have a small area, thus, greater pressure.

25. Pressure in Fluids
Fluids – exhibits fluidity (the
ability to flow);
Liquids and gases are fluids.

26. Pressure in Fluids
Pressure in fluids is same
throughout the container,
pressing equally on all the
sides of the walls.

27. Liquid Pressure
As you can see in a dam, the
walls is much thicker at the
bottom than it is at the top.
This is because the pressure
in liquids increases with depth.
Try to feel it by diving deeper
and deeper in a pool.

28. Liquid Pressure
Other applications of liquid
pressure:
• Deep-sea divers wear a
reinforced diving suit to work
safely at great depths.
• If there is a leak in the surface
of the submarine, water will be
forced inside.

29. Liquid Pressure
Other applications of liquid
pressure:
• Sometimes, water from the
faucet may come out slowly if
the water supply tank is lower
than the faucet. People living in
higher stories can sometimes
experience water shortage.

30. Liquid Pressure
Other applications of liquid
pressure:
• You don’t need to use a
tabo to scoop out the
water in your aquarium.
You siphon the water using
a hose pre-filled with water
then placing it in the
aquarium.

31. Air Pressure
• Pressure is created as
molecules collide to the
walls or with each other.
• The more collisions, the
greater the pressure.

32. Air Pressure
• Also called atmospheric
pressure.
• Measured in atmosphere
(atm). 1 atm = 101.325 kPa
• Air pressure is inversely
proportional with altitude.
The more we go up,
pressure becomes less.

34. Air Pressure
• In mount Everest, the tallest
mountain, pressure is just a
third of what it is at sea
level.
• In the stratosphere, air
pressure is only 1/100. The
more we go up to space, it
will decrease until pressure
becomes zero.

35. Air Pressure
• There is pressure everywhere, but how come we don’t get
squeezed by it?
• Because of our lungs. It has lower pressure than the
atmosphere.
• Note that force moves from higher pressure to lower
pressure. If the lungs have higher pressure, air and fluids in
the body will go out of the body and the body will explode
and die.

36. Air Pressure
• That’s why when you travel up a
mountain or in a higher place, you feel
that your ears become a little deaf.
That is because the ear is adjusting to
less air pressure.
• Also when an airplane goes up, it is
pressurized. There is a little pressure
up there, enough to make your lungs
and blood vessels explode.

37. Concept Micro
• Anything that has weight exerts a downward force. The
force exerted over an area is called pressure.

38. Sources:
Science Links 7