Physics-High-school-Fluid

Main Menu

Problem# h2phy1 - Pressure inside the Aorta

Problem# h2phy2 - Pressure on the floor

A living room has floor dimension of 3.5 m and 4.2 m and height of 2.4 m.
a. What does the air in the room weight?
b. What force does the atmosphere exert on the floor of the room?

Strategy - the rule "Must have" of Mr.Zhang ® material for solving this problem ; (1) w=mg    (2) m=ρv    (3) ρ=F⊥/A

Material or Object         Density (kg/m3)     Air: 20 οC and 1 atm 1.21

Solution a) The air in the room weighs;  w=mg    →(1)  m=ρv    →(2) We take (2) substitue in (1) ∴  W=ρairvg ∴  W = (1.21 kg/m3)(3.5 m x 4.2 m x 2.4 m)(9.8 m/s2 ∴  W = 418 kg m/s2 ∴  W = 418 N

Ans.   ∴The air in the room weighs 418 N

b) What force does the atmosphere exert on the floor of the room?  ρ=F⊥/A  ρatm=F⊥/A  F⊥=ρatmA  F⊥=1.01x105 N/m2)(3.5 m x4.2 m)  F⊥=1.5x106 N

Ans.   ∴The atmosphere exerts 1.5x106 N on the floor of the floor Brake Booster

Physics high school-fluid

Main Menu
Problem# h2phy2 - Pressure on the floor
Problem# h2phy1 - Blood Pressure inside the Aorta

The average gauge pressure in the human aorta is about 100 mmHg.
Convert this average blood pressure to pascals.

Strategy - the rule "Must have" of Mr.Zhang ® memorized (1)Atmospheric pressure,(2)Gauge pressure,(3)Absolute pressure.

Atmospheric pressure (Pa)

Barometer is a measurement tool for measuring air pressure. Barometers measure the current air pressure at a particular location in "inches of mercury" or in "millibars" (mb).

How much pressure are you under? Earth's atmosphere is pressing against each square inch of you with a force of 1 kilogram per square centimeter (14.7 pounds per square inch).

1 atm is calculated by formulae pHggh    →  pHg=13.6x10 3 kg/m3 Therefore, 13.6x103 kg/m3x9.8 m/s2x0.76 m.=1.01325x105Nm-2 =1.01325x105Pa = 1 atm

1 atm = 760 mmHg = 760 torr = 29.9 in.Hg =101.325 kPa = 14.7 lb/in.2

Gauge pressure (Pg) is the pressure according to the liquid substance only,at the height level point "h", and it can be calculated by the liquid weight. We calculate the gauge pressure with pgh

Absolute pressure (P) The difference between absolute pressure and atmospheric pressure is called gauge pressure.

P =  (Pg) + (Pa)

Absolute pressure - Atmospheric pressure = Gauge pressure

Solution

Ans.   The average blood pressure is converted to 13.3 kPa

Brake Master Cylinder

brake-shoe-physics-ฟิสิกส์มัธยมปลาย-ฟิสิกส์ ม.5

Main Menu

Problem h2b1: Brake system;Disc brake

Problem h2b2: Brake system;Drum brake

Consider the automobile hydraulic system shown in Figure a
A force of 100 N is applied to the brake pedal, which acts on the cylinder-called
the master-through a lever. The master cylinder has a diameter
0.500 cm. The slave cylinder (Drum brake) has a diameter 2.50 cm.
Calculate the force at each of the slave cylinders.

Strategy

Force is increased by the simple lever, and again by the hydraulic system.

Pascal's law - pressure applied anywhere to a body of fluid causes a force to be transmitted equally in all directions; the force acts at right angles to any surface in contact with the fluid; "the hydraulic press is an application of Pascal's law"

Solution

1. We take "O" to be fulcrum to find F₁

Then 500 N. is exerted on the master cylinder.
Pressure created in the master cylinder is transmitted to four so-called slave cylinders.
Then we calculate the Force at the slave cylinders each.
The circle cross sectional area of master and slave cylinder are A₁  A₂  respectively.
Hence we can find the force  F₂  at the brake drum.

Ans.   The force at each of the slave cylinders is 1.25 x 10⁴ N.

Brake Shoe

Braking system

Main Menu

Example 8: Brake system

Consider the automobile hydraulic system shown in Figure 1.
A force of 50 N is applied to the brake pedal, which acts on the cylinder-called
the master-through a lever. The master cylinder has a cross sectional area of
0.001 m. square. The slave cylinder has a cross-sectional area of 0.002 m. square
Figure shows the driver exerts a force on a hydraulic braking system of a car
on the brake pedal.
Calculate :

1) The force created at cylinder A		2) The pressure created in the fluid B.
3) The pressure created in the fluid C.		4) Force created at Disc Brake.
Force which acts against Disc brake in according to no.4, would be greater or less when ........
5) The 'O' point is closer to the fulcrum.
6) Cross-sectional area of cylinder A decreases.

Strategy

Force is increased by the simple lever, and again by the hydraulic system.

Pascal's law - pressure applied anywhere to a body of fluid causes a force to be transmitted equally in all directions; the force acts at right angles to any surface in contact with the fluid; "the hydraulic press is an application of Pascal's law"

Solution

1. The force created at cylinder A,

Ans.   The force created at cylinder A is 100 N.

2.The pressure created in the fluid B.
pressure created against cylinder A = pressure created in the fluid B

Ans.   The pressure created in the fluid B is

3) The pressure created in the fluid C.
pressure created in the fluid C = pressure created in the fluid B

Ans.   The pressure created in the fluid C is 

4) Force which created at Disc Brake.
Force created at Disc Brake = Force created at cylinder D

Ans.   Force created at Disc Brake is 200 N.

5)The 'O' point is colser to the fulcrum.
Ans. If point O is the position of the piston rod A, which is closer the fulcrum point.
When exert force is at the brake pedal as equal as prime, the more force will
be created on the cylinder A according to the lever class 2. Resulting pressure
in the fluid B and C increased,therefore, more force created at Disc brake.

6) Cross-sectional area of cylinder A decreases.
Ans. If the cross-sectional area of ​​the cylinder A decreases as the system with the same lever
and brakes, the pressure in the liquid B and C will be increased (as defined by the pressure
and Pascal's law), and will cause the more force at the Disc Brakes.

Brake Disc - Ford Duratorq

Hydraulic Lift

Main Menu

"F" exerted on the small piston at the end of the beam. Then fluid will flow through a valve 'a' toward large cylinders. Pull upwards the end of the beam, and the small piston will move upwards, valve 'a' will block the fluid reverse. Valve 'b' is open to let the fluid from the storage tank flow into a small cylinder. When you press the beam down again, the fluid will flow into the big cylinder again. Repeatly the cycle move up and down in several times to make fluid level more in the big piston to be able to lift a weight W higher. To let the weight W dropping down ,just open valve 'c', and fluid will allowed to flow into the storage tank.

Example 9.4 Hydraulic Lift The big piston of the oil jack lift the car,and the surface area of it is 100 times of smaller one. To lift the car mass 1200 kg, how many newtons is the force required to push at a small piston Strategy

Pascal's law - pressure applied anywhere to a body of fluid causes a force to be transmitted equally in all directions; the force acts at right angles to any surface in contact with the fluid; "the hydraulic press is an application of Pascal's law" Solution According to Pascal's law; We give the surface area of the big piston is "A", and the small piston is "a". Big piston and small piston will occupy same level of the fluid. Formulae is ;

Ans. The force required to push at a small piston is 117.6 N

"มืดมาสว่างไป" อันนี้ถือว่าสุดยอดสร้างกุศลเพื่อเป็นเสบียงเอาไว้ ฟันฝ่าอุปสรรคสามารถสร้างกุศล สำหรับชาตินี้ได้เยี่ยมครับ

"มืดมามืดไป" อันนี้ถือว่าไม่ประสบความสำเร็จ มีทุนเก่ามาน้อยมาก ต้องมีอุตสาหะมากมากในชาตินี้ ก็น่าเห็นใจครับ แต่ทำไงได้ สร้างมาอย่างไร ก็ต้องรับไปอย่างนั้น

"สว่างมามืดไป" อันนี้ถือว่าล้มเหลวในชีวิต ไม่สร้างกุศล ไม่สะสมเลย น่าเสียดาย น่าเสียดาย แล้วคิดจะมาเปรียบเทียบอะไรกับคนอื่นที่เขาร่ำรวย นั่นนะของเก่าเขาบำเพ็ญมา

"สว่างมาสว่างไป" อันนี้ถือว่ากุศลเก่าสร้างมาเยอะ ก็นำมาต่อทุนใหม่ ยิ่งสร้างเสบียงเพิ่มมากขึ้น ได้สบายสบาย

เวลาไม่ได้เหลือเยอะเลย ทุกลมหายใจมีโอกาสเปลี่ยนแปลง

เมื่อมีโอกาส รีบสร้างกุศล สร้างได้มากหรือน้อยในแต่ละวันก็ทำไปครับ

ถ้าเรารู้ว่าเขาเป็นคน "ไม่ดี" เราต้องหลีกห่าง

เลือกคบหากับบัณฑิต ก็คือคนดี เขาก็จะแนะนำสิ่งดี ๆ มาให้กับเราและครอบครัวตลอด

"เวรกรรมมีจริงแน่นอนครับ"

เมื่อไหร่เขาบริโภคกรรมดีที่ทำมาในอดีตจนหมด เมื่อนั้นแหละกรรมชั่วที่ทำมา ก็จะทยอยวิ่งมา

ให้เขาได้ชดใช้ ฉนั้นกลับตัวกลับใจซะเถอะ ก่อนที่เวรกรรมที่ได้กระทำมาแล้วจะวิ่งมาหาทัน

มันเร็วมาก มันติดจรวด

Oil Jack

Buoyant Force

Main Menu

Exercise 2/95

A Balloon has no gas with basket are combined weight totally 500 kg. How much gas helium filled when the ballon can float motionless in the air? Solution Owning to the air is fluid, balloon floating in the air acts same as the buoyant force does inside the water. While the ballon floating in equilibruim(net force act to the balloon is zero.) Buoyant force  acting on the balloon is equal to the weight+  balloon with a basket "W"

Ans. Gas helium is filled 485 cubic m.

Exercise 1/92        Maker

Explorers travel by a gas balloon. Before he sets off, he has filled a helium gas which has volume 400 cubic metre and a mass of 65 kg. While a gas balloon is flying, how many density is the gas balloon occupied?

Solution 1. We get V = 400 cubic metre, m = 65 kg. 2. We want to know the the density [Rho (ρ)] 3. We pop up the formula ; ρ = m/v Then ; the density is

While a gas balloon is flying, the density of the gas balloon is 0.16 kg/cube meter. Ans.    ρ=0.16 kg./cube meter

Remark

1. Answer is possible. Why? Because the "ρ" of the weather is average 1.2 kg./cube meter. If the gas balloon is flown, it must have the density ("ρ") lower than the density ("ρ") average of the weather. 2.Noted that aluminum has a lower density compared to other metals, therefore airplane  is made of aluminum. In addition, Aerogel is the world's least dense solid.

How can the airplane  fly?

pressure

Main Menu

Exercise 1.        Maker

Explorers travel by a gas balloon. Before he sets off, he has filled a helium gas which has volume 400 cubic metre and a mass of 65 kg. While a gas balloon is flying, how many density is the gas balloon occupied?

Solution 1. We get V = 400 cubic metre, m = 65 kg. 2. We want to know the the density [Rho (ρ)] 3. We pop up the formula ; ρ = m/v Then ρ = 65 kg.

While a gas balloon is flying, the density of the gas balloon is 0.16 kg/cube meter. Ans.    ρ=0.16 kg./cube meter

Remark

1. Answer is possible. Why? Because the "ρ" of the weather is average 1.2 kg./cube meter. If the gas balloon is flown, it must have the density ("ρ") lower than the density ("ρ") average of the weather. 2.Noted that aluminum has a lower density compared to other metals, therefore airplane is made of aluminum. In addition, Aerogel is the world's least dense solid.