Introduction

Why there must be a gap between two rail bars (rail way track)?

EXPANSIONSCIENCE TEAM P26

Expansion

Solid Liquid Gas

Linear

Area

Volume

Volume

Illustration of particle’s movement

• Solid Particles• Liquid Particles• Gas Particles

• When the particles are heated, which one will expand faster?

Solid ExpansionThe bridges on the roads are generally made of steel which are connected to each other.

During the process of constructing the bridge, construction engineers consider the nature of expansion and contraction of the steel because of temperature changes, either at noon or night.

There is a gap on the bridge

Solid ExpansionSolids will expand when it is heated and contract when it is cooled.

Expansion happens because the atoms of an object vibrate faster than usual, so that its volume is bigger and its density decreases.

Linear Expansion of SolidLO

Lt

L

Before being heated

When being heated

The length change influence by:

1. The length of an object

2. The change of temperature

3. Kind of matter (material)

Linear Expansion

• The Formula of linear Expansion.

Forα = coefficient of linear expansion.Lo= The first length of the object∆T= The change in temperature∆L= The change in lengthΔL = L – Lo

∆T = T – To

).1(

..

TLL

TLL

o

o

).1(

)..(

..)(

..

TLL

LTLL

TLLL

TLL

o

oo

oo

o

EXCERCISE

Example:A train track which is made of steel has the length of 40 meters on 0

oC. How long is its expansion if it is heated until 100 oC?Known Lo = 40 meters

∆T = 100 oC - 0 oC = 100 oCαsteel = 0.000011/oC

Question: ∆L = ?Equation: ∆L = Lo . α . ∆TSolution:

∆L = (0.000011/oC) (40 meter) (100 oC) = 0.044 meter

EXCERCISE• The length of plastic is 20 cm at 20 oC and when the temperature

rise at 140 oC, the plastic is longer be 80 cm. How the plastic linier coefficient is?

• By the question knowed: T0 = 20 oCT = 140 oC

L0 = 20 cmL = 80 cm

Asked: ?Answer: L = L0 1+ (T-T0)

80 = 20 1+ (140-20) 4 = 1 + . 120 = 0,025 oC-1

So that, the linier coefficient of length expansion is 0,025 oC-1

Area Expansion

Area expansion in solid

The area expansion coefficient is twice the linear coefficient.The formula of area expansion :

The Formula of Area Expansion.

Forβ = coefficient of area expansion.Ao= The first area of object∆T= The change in temperature∆A= The change in areaβ = 2.α

).1(

..

TAA

TAA

o

o

Volume Expansion

Volume expansion in solidThe volume expansion

coefficient is three times larger than the linear expansion coefficient.

The formula of volume expansion is

).1(

..

TVV

TVV

o

o

The Formula of Volume Expansion.

Forγ = coefficient of volume expansion.Vo= The first volume of the object∆T= The change in temperature∆V= The change in volumeγ = 3.α

The examples of the use of expansion or contraction in daily life is

1. Bimetal.

Steel of Brass of

Brass

Steel

Bimetal is heated Bimetal is cooled

Bimetal

• Bimetallic Strip: Brass, = 19 x 10-16 /Co

Steel, = 12 x 10-6 /Co

MaterialThe length expansion

coefficient (/oC)

Glass 9 x 10-6

Pyrex Glass 4 x 10-6

Aluminum 24 x 10-6

Brass 19 x 10-6

Steel 13 x 10-6

Iron 12 x 10-6

Bimetal Thermostate

*Thermostat is a device which keep a building, engine,etc, within a ussualy limited temperature range, by automatically switching on-off.

* Bimetallic strip is a strip used in thermostat, made of two different metals which expand with different amount, when it heated.

*The principle of bimetal is based on the different linier expansion coefficient of two metals are packed each other.The function of a bimetal as automatic switch

1. Bimetal2. thermostat

3. automatic switch in an electric iron 4. the track of the train and

5. bridge connectors are given a space.

Application of Solid Expansion

Main Activity

Indicator

Metal Bar

Burner

Screw

Musschenbroek Apparatus

MUSSCENBROEK

Musschenbroek Apparatus

• It can be used to find the increasing length (expansion of different metals) when being heated.

Data and observation

Not move

Not move

Not move

Move

Move

Move

MetalPosition of indicator needle before being

heated

Position of indicator needle after being heated

Note

Steel

Aluminum

Copper

MaterialThe length expansion

coefficient (/oC)

Glass 9 x 10-6

Pyrex Glass 4 x 10-6

Aluminum 24 x 10-6

Brass 19 x 10-6

Steel 13 x 10-6

Copper 17 x 10-6

5 scale

10 scale

6 scale

Which one is the longest metal when being heated?

Aluminum

Why does the aluminum have the longest linear expansion?

Conclusion

“Expansion is increase in size of a matter, if it heated.

3 Kinds of expansion are solid expansion, liquid expansion, and gas

expansion.”

The length change is influenced by:

1. The length of an object

2. The change of temperature

3. Kind of matter (material)

It can be formulated as follows:

TLL o ..

.

EXCERCISES

Answer these questions correctly!

1. Why a gap is given between rail road ?2. What is bimetal?3. What is the function of bimetal in a electric iron?4. What is the function of thermostat ?5. Can you mention the working principle of thermometer?

Good luck!

Excercise!Answer these questions correctly!1. What is expansion? Explain.2. Give 3 examples of expansion in daily life!3. When do the objects expand? Explain.4. Mention the factors that influence expansion!5. What kind of formula to find the changing of length of

linear expansion!6. What instrument do you use to find the linear expansion?7. The initial length of iron is 30 m at 25 ˚C. if it’s heated up

to 90 ˚C. Determine the length of iron after being heated. Given linear expansion coefficient of iron is 0.000012 /C˚!