8/18/2019 Unit 1.5 – Materials - Fluid Flow

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[UNIT 1 – PHYSICS ON THE GO – 2.0 MATERIALS]   1

1.5 FLUID FLOW

1. Density, Upthrust, Flows, Viscous Drag and Terminal

Velocity

2. Relationship between Rate of Flow Viscosity!. "to#es$ %aw,

&. 'hange of Viscosity with Temperature

1. Density, Flows, Upthrust, Viscous Drag, and Terinal

Velocity

Fluid ( "ubstance that can flow. )enerally li*uid n gas.

Density ( +easure of mass per unit olume

Density,  ρ=m

V  

where m ≡  mass, #gV ≡  olume, m!

Upthrust ( is the force caused by fluid pressure.

( e*uals to weight o! the !luid that has "een displaced by an

ob-ect /rchimedes 0rinciple

3 mg

3  ρ Vg

45ample 1

/ cubic wooden bloc# of 26 cm lengths is floating on water.

'alculate the height of the submerged portion of the bloc#. Thewood used has a density of 766 #gm!

For a floating ob-ect, Upthrust 3 eight

eight of bloc# 3  ρ Vg

3 766 6.256.256.2 8.91

3 !8.2& :

Upthrust weight of water 3  ρ Vg

!8.2& 3 16666.2 5 6.2 5 h8.91h 3 6.1 m or 16 cm

 Explain the principles involved in the sinking of an object.

Similarly explain how a metal ship does not sink.

/n ob-ect will sin# if the weight of the li#uid displaced is higher

than the upthrust.

/ metal ship does not sin# because it is design in such a way that it

displaces enough water to create an upthrust which is higher than theweight of the water.

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 How does a hydrometer work?

Flows

2 types ( Lainar streamline flow and Tur"ulent flow

%aminar flow occurs at lower speeds and will change into

turbulent flow as elocity increases.

Demonstrating types of flow;

using a glass tube. "ee

ideo.

"ee page 7

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[UNIT 1 – PHYSICS ON THE GO – 2.0 MATERIALS]   3

2. Relationship between Rate of Flow and Viscosity

 

The more iscous the fluid is, the harder it is for an ob-ect to

moe.

Thus, iscosity is inersely proportional to rate of flow.

through e5periments

!. "to#es$ %aw

Viscous Drag

( the >friction$ acting in a fluid which restricts moement.

coefficient of iscosity, η  ? @

the higher the iscosity, the slower it flows

Viscous drag, F 3 A   πrηv

where r ≡  radius of sphere, m  η≡  coefficient of iscosity, 0a s

v   ≡  elocity of the sphere, ms1

Terinal $elocity

( occurs when ob-ect is sin#ing or falling with constant elocity.

Therefore,eight 3 Uptrust B Viscous Drag

&. 'hanges of Viscosity with Temperature

"ee page 78

ith li*uids,

Viscosity CCCCCCCCCC with temperature.

ith gases,

Viscosity CCCCCCCCCC with temperature.

45plain the aboe.

=n li*uids,

/s temperature increases, the attractie force between molecules is

oercomed, which results in the li*uid easier to flow.

=n gases,

/s temperature increases, air molecules ibrate more *uic#ly in

many directions which results in the gas being harder to flow.

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[UNIT 1 – PHYSICS ON THE GO – 2.0 MATERIALS]   5