Haba

What is Heat?

• Suatu bentuk tenaga - kerana ia boleh menggerakkan benda

- E.g: Makes a hot air balloon rise.

- Steam engines

• Diukur dalam unit

JOULES (J)

Haba

Haba adalah bentuk tenaga yang boleh mengalir dari kawasan panas ke kawasan sejuk

Haba boleh bertukar bentuk

• Proses fotosintesis ( Tumbuhan membuat makanan)

Tenaga cahaya & haba → Tenaga kimia

• Stesen Jana kuasa (Pembakaran minyak dan gas)

• Tenaga haba → Tenaga kinetik →

Tenaga elektrik

Bagaimana haba dihasilkan?

• Pergerakan zarah-zarah menghasilkan haba.

• Haba dapat dihasilkan melalui geseran, pembakaran bahan api, tenaga elektrik dan sebagainya.

• Haba menyebabkan pengembangan dan pengecutan pepejal, cecair dan gas.

Haba Vs Suhu

• The temperature of an object tells us how HOT it is

• Ukuran darjah kepanasan atau kesejukkan suatu objek.

• Measured in degrees Celsius - °C

Haba Vs Suhu

• It is NOT the same as heat energy although the two quantities are related.

• e.g. a beaker of water at 60 °C is hotter than a bath of water at 40 °C BUT the bath contains more joules of heat energy

Pengaliran haba

• Mengalir dari kawasan yang panas ke kawasan yang sejuk.

• Objek panas dalam bilik akan menjadi sejuk ke takat suhu bilik.

e.g: air kopi

• Objek sejuk dalam bilik akan dipanaskan ke takat suhu bilik.

e.g: butter, ice

What do you think?

Pengaliran haba

3 cara

• Konduksi/ Conduction

• Perolakan/ Convection

• Sinaran/ Radiation

Konduksi/ Conduction• Pengaliran haba dari kawasan panas ke

kawasan sejuk pada suatu pepejal.

• Zarah-zarah pada satu hujung rod pepejal yang dipanaskan memperolehi tenaga haba dan bergetar dengan lebih cepat dan berlanggar dengan zarah-zarah bersebelahan.

• Tenaga haba dipindahkan kepada zarah-zarah bersebelahan secara berterusan dan akhirnya ke seluruh rod logam.

Konduksi/ Conduction• When you heat a metal strip at one end, the heat travels

to the other end.

• As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this? Conduction

Why does metal feel colder than wood, if they are both at the same temperature?

Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

Perolakan/ ConvectionWhat happens to the particles in a liquid or a gas when you heat them?

The particles spread out and become less dense.

A liquid or gas.

Perolakan/ Convection• Proses pengaliran haba melalui bendalir

(cecair dan gas) akibat gerakan bendalir dari kawasan yang lebih panas ke kawasan yang kurang panas.

Perolakan/ Convection

• Think about when you boil water, the bubbles move upwards

• Or think of a gas heater in the room, the heat rises around the room

Perolakan/ Convection

Hot water rises

Cooler water sinks

Convection current

Cools at the surface

Perolakan/ ConvectionWhere is the

cooling compartment

put in a fridge?

Cooling compartment

It is put at the top, because cool air

sinks, so it cools the food on the way

down.

It is warmer at the bottom, so this warmer air

rises and a convection

current is set up.

Convection questions

Why are boilers placed beneath hot water tanks in people’s homes?

Hot water rises.

So when the boiler heats the water, and the hot water rises, the water tank is filled with hot water.

Why does hot air rise and cold air sink?

Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.

How does heat energy get from the Sun to the Earth? There are no particles

between the Sun and the Earth so it CANNOT travel by conduction or by convection.

?RADIATION

Sinaran/ Radiation

• Proses pemindahan haba daripada suatu sumber haba ke kawasan persekitarannya tanpa medium

• Mengalir ke semua arah daripada objek yang panas.

• Semakin panas objek, semakin banyak haba yang mengalir melalui sinaran.

• Does the surface affect the way heat is radiated?

Radiation – Think Pair-ShareRadiation travels in straight lines

True/False

Radiation can travel through a vacuum

True/False

Radiation requires particles to travel

True/False

Radiation travels at the speed of light

True/False

Radiation questions

Why are houses painted white in hot countries?

White reflects heat radiation and keeps the house cooler.

Why are shiny foil blankets wrapped around marathon runners at the end of a race?

The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.

Konduktor haba dan penebat haba

• Konduktor haba – bahan yang membenarkan haba melaluinya dengan mudah. e.g: most metals

• Penebat haba – bahan yang menghalang haba mengalir melaluinya. e.g: wood, plastic, glass

• Why do many sauce pans have plastic handles?

Konduktor haba Vs Penebat haba

Conductor or Insulator?• Wood?

• Aluminium?

• Plastic?

• Glass?

• Iron?

• Polystyrene?

• Copper?

• Cardboard?

Pelbagai Kegunaan konduktor dan penebat dalam kehidupan harian

Bincangkan…

Pemanas pada dasar cerek elektrik

Periuk dan kuali

Seterika elektrik

Radiator kereta

Merkuri

Kotak ais

Pelbagai Kegunaan konduktor dan penebat dalam kehidupan harian

Rajah di sebelah menunjukkan struktur binaan sebuah kelalang termos. Struktur binaan kelalang termos bertujuan untuk mengurangkan kehilangan haba. Bincangkan.

Penyerap dan Pembebas haba yang Baik

• Keupayaan suatu objek untuk menyerap dan membebaskan haba dipengaruhi oleh ciri permukaan objek (jenis dan warna)

• Permukaan yang gelap dan kusam menyerap dan membebaskan haba lebih baik daripada objek putih dan berkilat

Emission experiment

Four containers were filled with warm water. Which container would have the warmest water after ten minutes?

Shiny metal

Dull metal

Dull black

Shiny black

The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. The ________ container would be the coolest because it is the best at _______ heat radiation.

shiny metalradiation

dull blackemitting

Absorption experiment

Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes?

The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation.

dull blackradiation

shiny metalabsorbing

Shiny metal

Dull metal

Dull black

Shiny black

EmittersEmittersHotter objects emit (give out) heatDifferent surfaces emit heat at different speedsA dull black surfaces loses energy more

quickly – it is a good radiatorA bright shiny or white surface is a poor

radiatorMarathon runners need to keep warm at the end

of races, covering in shiny blankets reduces radiation and therefore heat loss.

Emitters of heatEmitters of heat

Bright shiny canPoor radiator

Dull black canGood Radiator

AbsorbersAbsorbersCooler objects absorb (take in) heat

Substances absorb heat at different speeds

Dull, black surfaces absorb heat quickly

Bright, shiny surfaces absorb heat slowly

In hot countries, people wear bright white clothes and paint their houses white to reduce absorption of energy from the sun.

Petrol storage tanks sprayed silver to reflect sun’s rays

AbsorbersAbsorbers

Shiny, bright canPoor absorber

Dull black canGood absorber

Revision1. Which of the following is not a method of heat transfer?

A. RadiationB. InsulationC. Conduction

D. Convection

Revision1. Which of the following is not a method of heat transfer?

A. RadiationB. InsulationC. Conduction

D. Convection

2. In which of the following are the particles closest together?

A. SolidB. LiquidC. Gas

D. Fluid

2. In which of the following are the particles closest together?

A. SolidB. LiquidC. Gas

D. Fluid

3. How does heat energy reach the Earth from the Sun?

A. RadiationB. ConductionC. Convection

D. Insulation

3. How does heat energy reach the Earth from the Sun?

A. RadiationB. ConductionC. Convection

D. Insulation

4. Which is the best surface for reflecting heat radiation?

A. Shiny whiteB. Dull whiteC. Shiny black

D. Dull black

4. Which is the best surface for reflecting heat radiation?

A. Shiny whiteB. Dull whiteC. Shiny black

D. Dull black

5. Which is the best surface for absorbing heat radiation?

A. Shiny whiteB. Dull whiteC. Shiny black

D. Dull black

5. Which is the best surface for absorbing heat radiation?

A. Shiny whiteB. Dull whiteC. Shiny black

D. Dull black

Key Words

Heat

Radiation

ConvectionConduction

Cold

Insulator

Conductor

Temperature

EmitAbsorb

Transfer