(4) PHY08221-Biofisika-5 Fluida Statis

KULIAH 5

Pokok Bahasan : BIO-MEKANIKA (FLUIDA)

Sub Bahasan : Fluida Statika: Fenomena fisika hayati pada fluida statis (diam)

Fluida Dinamika: Fenomena fisika hayati pada fluida dinamis (mengalir)

Tujuan Pembelajaran, mahasiswa mampu- menerapkan konsep tegangan permukaan dalam mengkaji fenomena

bergeraknya mahluk hidup di atas permukaan air

- menerapkan konsep perbedaan tekanan dan persamaan Bernouli dalam mengkaji aliran darah dalam tubuh

PUSTAKA RUJUKAN Krane, Joseph W and Morton M Sternheim (1978). Life Science Physics. John Wiley and Sons

IV. BIO-MEKANIKA (Fluida)

REVIEW FLUIDA STATIKA: Tekanan Hidrostatikhttp://www.physics.uc.edu/~sitko/CollegePhysicsIII/9-Solids&Fluids/Solids&Fluids.htm

Besaran fisis fluida: Massa jenis dan tekanan

Massa Jenis (densitas) (Nilai -zat bergantung pada suhu

Pressure in a fluid 

At any particular depth, the pressure is constant throughout a fluid.

Review Pengertian Tek Hidrostatik

JARUM INJEKSI: Syringe

Pascal's Law

Variation of static pressure with depth

http://www.coolingzone.com/library.php?read=482

po = 1.013x105 Pa at sea levelp increases with depth by an amount mgh.

NOTE that an increase in pressure applied to an enclosed fluid is transmitted undiminished to every point in the fluid (including the walls of the container)- Pascal’s Principle

 Variasi Tekanan: INFUS

Perbedaan tekanan antara cairan di BOTOL dan cairan yang masuk ke dalam pembuluh darah pasien dapat dihitung dari tekanan total, yaitu:

A collapsible plastic bag contains a glucose solution. If the average gauge pressure in the artery is 1.33x104 Pa, what must be the minimum height h of the bag in order to infuse glucose into the artery? Assume that the specific gravity of the solution is 1.02.

Variation of Pressure with DepthIn equilibrium, all points at the same depth must be at the same pressure. Otherwise a net force would be applied and the fluid would accelerate.

Tekanan “bekerja” di setiap titik arah gaya dalam posisi tegak lurus dan tidak memperhatikan bentuk benda, total massa ataupun luasan permukaan cairan.

Tekanan Hidrostatik: Penyebab kejang otot?

http://www.exrx.net/Store/VHI/Kits/AquaticExercise.html

 Pressure Measurements  

open-tube manometer

Note that P = absolute (true) pressure inside the bulb. P-P0 is the gauge pressure, the pressure that is added to the atmospheric pressure to equal P.

Barometer

1 atm. → pressure equal to a 0.76 m column of mercury at T=0C and g=9.80665 m s-2.

Prinsip kerja alat ukur tekanan darah: sphygnomanometer

Tekanan di titik A sama dengan tekanan di titik 1,

tekanan di titik 2 sama dengan tekanan di titik 1 + 1gh1.

Tekanan di titik 2 sama dengan tekanan di titik 3, yaitu 2gh2

Berdasarkan persamaan tekanan di titik 2 dan titik 3, maka didapat :

Jika A diisi udara, maka umumnya tekanan 1gh1 dapat diabaikan, karena massa jenis udara sangat kecil sehingga p2 » pA.

bilangan tekanan darah

Blood pressure is recorded as two numbers: the top number is called systolic pressure and the bottom number is called diastolic pressure.

http://home.comcast.net/~pegglestoncbsd/cardiovascular.htm

Tabel bunyi detak tensimeter: Korotkov sounds dapat dilihat di http://greenfield.fortunecity.com/rattler/46/bloodpressure.htm

Tekanan Normal blood pressures are said to range from 100/60

2211 ghghPA

darah normal dalam keadaan istirahat

mmHg to 150/90 mmHg.

Some 'average' blood pressures relating to age (year) in mmHg

Age Systolic

Diastolic

New-born 80 46

10 103 70

20 120 80

40 126 84

60 135 89

Ideal resting rate: http://www.buzzle.com/articles/resting-heart-rate-range.html

Classification of blood pressure for adults

Categorysystolic, mmHg

diastolic, mmHg

Hypotension < 90 < 60   

Normal  90 – 119 60 – 79   

Prehypertension 120 – 139 80 – 89  

Stage 1 Hypertension 140 – 159 90 – 99  

Stage 2 Hypertension ≥ 160 ≥ 100  

Chobanian AV, Bakris GL, Black HR, et al (December 2003). "Seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure". Hypertension 42 (6): 1206–52. doi:10.1161/01.HYP.0000107251.49515.c2. PMID 14656957.

Diseases and Conditions Index - Hypotension". National Heart Lung and Blood Institute. September 2008. http://www.nhlbi.nih.gov/health/dci/Diseases/hyp/hyp_whatis.html. Retrieved 2008-09-16.

Heart Rates for Various Mammals (beats/min)

http://www.physicscentral.com/explore/action/alive-1.cfm

Generally speaking, the larger the animal, the slower its resting heart rate.

Camels and bats represent the two extremes of the scale, with most other mammals falling somewhere in between.

http://math.arizona.edu/~maw1999/blood/rate.html

Whale 20 Horse 45 Human 70 Cat 150 Hamster 330

Blood pressureA measure of how hard blood is pressing against artery walls.

http://www.revolutionhealth.com/articles/how-high-blood-pressure-damages-arteries/zm6282

http://health.sykeschemists.co.uk/

. http://www.umm.edu/careguides/000358.htm

Blood pressure is the amount of pressure exerted on the walls of the arteries as the blood moves through them. Blood pressure is measured in terms of the millimeters column of mercury (in mmHg) that could be supported by the pressure inside the arteries at two times: maximum thrust by the heart, and when the heart is relaxed. These are normally about 120 mm and 80 mm, respectively. Recent medical guidelines suggest that the familiar old “normal” 120/80 values are too high, and that somewhat lower values are desired!

Titik-titik arteri (simpul); lokasi tekanan darah terdeteksi dengan kuat

http://www.blood-pressure-hypertension.com/blood-pressure/blood-pressure-1.shtml

Bed rest; relaxing your heart

Tekanan darah: selisih ketinggianEstimate the amount by which blood pressure changes in an actuary in the foot P2 and in the aorta P1 when the person is lying down and standing up. Take density of blood = 1060kg/m3

FLUIDA STATIKA: Tegangan Permukaan

Definisi Tegangan Permukaan

The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension.

Note that γ depends on temperature. At higher T, the molecules are not as tightly bound together. You can also alter the surface tension of fluids using additives.

If the surface becomes curved as in the picture below, it may support a weight. This is illustrated clearly below

Surface tension is actually defined as the force per unit length in a surface needed to hold the surface together:

If

the weight of the needle is W, resolve vertically for the needle:

CONTOH Tegangan Permukaan yang dialami serangga

The base of an insect's leg is approximately spherical in shape with a radius of about 2.0 × 10-5 m. The mass of the insect is 3.00 × 10-6 kg and is supported equally by six legs. Calculate the contact angle θ as shown in the diagram. The coefficient of surface tension is 0.072 N/m.

SOLUSI

radius of insect leg = R = 2.0 × 10-5 m mass of insect = m = 3.00 × 10-6 kg insect supported by 6 legs coefficient of surface tension = γ = 0.072 N.m-1 contact angle = θ = ? ° Assume the surface tension acts around the circle of radius R, where R is the radius of a leg. This is not accurate since the radius of the surface depression is not precisely the radius of the leg. Equilibrium

(2) (FT cos θ) = FG ; FT = (2π R) γ FG = m g / 6 (2π R) γ cos θ = m g / 6 cos θ = (m g) / {(12π R) γ}

cos θ = (3.00 × 10-6 )(9.8) / {(12π)(2.0 × 10-5)(0.072 )} cos θ = 0.54157

θ = 57°

If cos θ ≥ 1 or θ ≥ 90° ⇒ surface tension would not support insect.

Pressure and Blood Flow

The higher the pressure exerted by the heart, the faster blood will flow.

Another factor which controls the blood flow rate is the resistance of the blood vessels to blood flow.

flow rate of blood in aorta?Calculate the flow rate of blood (of density 0.722 g/cm3) in an aorta with a cross-sectional area of 2.67 cm2 if the flow speed is 36.6 cm/s. Answer in units of g/s.

Assume the aorta branches to form a large number of capillaries with a combined cross-sectional area of 1820 cm^2. What is the flow speed in the capillaries? Answer in units of cm/s.

use the equation m = p * v * A = 0.722 * 36.6 * 2.67 = 70.555284 g/s.

for the second question,use conservation of flow rate: p v A = p v a, 70.555 = 0.722 * v * 1820, v = 0.0536931905 cm/s