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 alirandarah dalam tubuh

PUSTAKA RUJUKANKrane, 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 fisisfluida: Massajenis dan tekanan Massa Jenis (densitas) (Nilai -zat bergantung pada

suhu

Pressure in a fluid

At any particular depth, the pressure is constantthroughout a fluid.

ReviewPengertian TekHidrostatik

JARUM INJEKSI: Syringe

Pascal's Law

Variation ofstatic pressurewith 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 transmittedundiminished to every point in the fluid (including the walls of the container)-Pascal’s Principle

AFPPressure

darahcairan PP

darahtabung

dorong PAF

tabungdarahdorong APF

Variasi Tekanan: INFUS

Perbedaan tekanan antara cairan di BOTOL dan cairan yangmasuk ke dalam pembuluh darah pasien dapat dihitung daritekanan total, yaitu:

A collapsible plastic bag contains aglucose solution. If the average gaugepressure in the artery is 1.33x104 Pa,what must be the minimum height h ofthe bag in order to infuse glucose intothe artery? Assume that the specificgravity of the solution is 1.02.

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

Tekanan “bekerja” di setiap titik arah gaya dalamposisi tegak lurus dan tidak memperhatikanbentuk benda, total massa ataupun luasanpermukaan cairan.

ghPghPPghPP

0

0

Tekanan Hidrostatik: Penyebab kejang otot?

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

Pressure Measurements

open-tube manometer

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

Barometer

1 atm. → pressure equal to a 0.76 m column of mercury atT=0 -2.

Prinsip kerja alat ukur tekanan darah: sphygnomanometer

Tekanan di titik A sama dengan tekanan dititik 1,

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

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

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

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

bilangantekanan darah

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

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

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

2211 ghghPA

22ghPA

Tekanandarah normaldalamkeadaanistirahat

Normal blood pressures are said to range from 100/60 mmHg to150/90 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

Category systolic, 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 JointNational Committee on Prevention, Detection, Evaluation, and Treatment of High BloodPressure". Hypertension 42 (6): 1206–52. doi:10.1161/01.HYP.0000107251.49515.c2. PMID14656957.

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. Retrieved2008-09-16.

Heart Ratesfor VariousMammals(beats/min)

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

Generally speaking, the larger the animal, the slower its resting heartrate.

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

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

Whale 20 Horse 45 Human 70Cat 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 pressureexerted on the walls of the arteries as the bloodmoves through them. Blood pressure ismeasured in terms of the millimeters column ofmercury (in mmHg) that could be supported bythe pressure inside the arteries at two times:maximum thrust by the heart, and when theheart is relaxed. These are normally about 120mm and 80 mm, respectively.

Recent medical guidelines suggest that thefamiliar old “normal” 120/80 values are too high,and that somewhat lower values are desired!

Titik-titikarteri(simpul);lokasi tekanandarahterdeteksidengan kuat

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

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

PaPPdings

PaghPPdownLying

412

12

104.135.1*8.9*1060tan

0

FLUIDA STATIKA: Tegangan Permukaan

DefinisiTeganganPermukaan

The cohesive forcesbetween liquidmolecules areresponsible for thephenomenon known assurface tension.

Note that γ depends ontemperature. At higherT, the molecules are notas tightly boundtogether. You can alsoalter the surface tensionof fluids using additives.

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

Surface tension isactually defined asthe force per unitlength in a surfaceneeded to hold thesurface together:

If the weight of the needle is W, resolvevertically for the needle:

CONTOH Tegangan Permukaan yang dialami serangga

The base of an insect's leg isapproximately spherical in shapewith a radius of about 2.0 × 10-5

m. The mass of the insect is 3.00× 10-6 kg and is supportedequally by six legs. Calculate thecontact angle θ as shown in thediagram. The coefficient ofsurface tension is 0.072 N/m.

SOLUSI

radius of insect leg = R = 2.0 × 10-5 mmass of insect = m = 3.00 × 10-6 kginsect supported by 6 legscoefficient 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 aleg. This is not accurate since the radius of the surface depression is not precisely theradius 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.

Pressureand BloodFlow

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

Another factor which controls theblood flow rate is the resistance ofthe 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 combinedcross-sectional area of 1820 cm^2. What is the flow speed in the capillaries? Answer inunits of cm/s.

use the equationm = 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