heat and momentum

8/10/2019 Heat and Momentum

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T R A N S F E R

HEAT AND MOMENTUM


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HEAT TRANSFER

Principle The driving force foratmospheric motion is the sunand, in particular, the unevendistribution of solar radiation

across the earth.

It is the primary job of theatmosphere to redistributeenergy in order to achieve abalance from pole to equator.

We need to understandmethods of heat exchange inthe atmosphere to appreciatehow the thin atmosphere keepsus alive.


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ENERGY

Energy is the ability or capacity to do work on some form of matter. There are several forms of energy, including the following

Potential energy is the energy which a body possesses as a consequence of itsposition in a gravitational field (e.g., water behind a dam).

Kinetic energy is the energy which a body possesses as a consequence of its motion(e.g., wind blowing across a wind generator). It is dependent upon an object's massand velocity (e.g., moving water versus moving air).

Internal energy is the total energy (potential and kinetic) stored in molecules. Heat (or thermal) energy is kinetic energy due to motion of atoms and molecules. It is

energy

that is in the process of being transferred from one object to another becauseof their temperature difference.

Radiant energy is the energy that propagates through space or through materialmedia in the form of electromagnetic radiation.

The First Law of Thermodynamics states that energy lost during one

process must equal the energy gained during another.


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.. LATENT HEAT

Latent heat is the heat energy required to change a substance from onestate to another. There are basically three states of matter: solid, liquid,and gas. The difference between them is how the molecules arearranged. Solids have tightly-packed molecules, liquids are still boundtogether but not strongly enough to keep them from flowing, and gasmolecules are free-flowing, not bound to one another at all. Energy is

required to change from one state to another because bonds must beloosened, broken, tightened, or made. Energy must be given to themolecules if bonds are to be loosened or broken and taken from themolecules if they are to be tightened or made.

Latent heat of evaporation is the energy used to change liquid to vapor.

IMPORTANT: The temperature does not change during this process, soheat added goes directly into changing the state of the substance.About 600 calories of energy are needed for every gram of water atroom temperature. This is why you cool when you step out of the shower.Heat is taken from your skin to evaporate the water on your body.


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LATENT HEAT.


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Energy is required to change from solid to liquid, liquid to gas (evaporation), or solidto gas (sublimation). Energy will be released to change from liquid to solid (fusion),gas to liquid (condensation), or gas to solid.

Evaporation is a cooling process. Latent heat of condensation is energy released when water vapor condenses to

form liquid droplets. An identical amount of calories (about 600 cal/g) is released inthis process as was needed in the evaporation process. This is one mechanism ofhow thunderstorms maintain their intensity. As moist air is lifted and cooled, watervapor eventually condenses, which then allows for huge amounts of latent heatenergy to be released, feeding the storm.

Condensation is a warming process. Latent heat of fusion describes both changing from solid to liquid and from liquid to

solid. From solid to liquid, about 80 calories per gram are needed. From liquid tosolid, about 80 cal/g are released.

Latent heat of sublimation describes both changing from solid to gas and gas tosolid. Sublimation is rare as compared to the other changes of state. From solid togas 600 + 80 = 680 calories per gram are needed. From gas to solid, 680 cal/g arereleased.


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METHOD

Conduction energy is transferred by the direct contact of molecules, notby the movement of the material Example: putting your hand on a stoveburner. The amount of energy transferred depends on how conductivethe material is. Metals are good conductors, so they are used to transferenergy from the stove to the food in pots and pans. Air is the bestinsulator, so good insulating products try to trap air and not allow it to

move. Convection energy is transferred by the mass motion of groups of

molecules resulting in transport and mixing of properties Example: holding your hand over a stove burner. In meteorology, we

speak of convection predominantly as that caused by rising currents ofwarm air. We refer to all other mass motions of air as advection.

Radiation energy is transferred by electromagnetic radiation Example: heat felt when standing away from a large fire on a calm night.

Everything that has a temperature above absolute zero radiates energy.Radiation is not "felt" until it is absorbed by a substance. It does notrequire a medium to transfer energy through as do conduction andconvection.


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SPESIFIC HEAT

Specific heat is the amount of heatneeded to raise the temperature ofone gram of a substance onedegree Celsius.

The specific heat of water is veryhigh compared to other substances,

so water can store energy longerthan most other substances. Forexample, the Gulf of Mexico remainswarm during the night, when air andsoil temperatures decrease rapidly.

Why is the Southern Hemispheresummer generally not warmer thanthe Northern Hemisphere summeralthough Earth is closer to the sunduring the Southern Hemispheresummer? Because most of theSouthern Hemisphere is water, whichregulates the seasonal temperatures.


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KONDUKSI, KONVEKSI, RADIASI


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RADIASI


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MEKANISME RADIASI

Jika radiasi mengenai tubuh manusia, ada 2kemungkinan yang dapat terjadi :

Jika berinteraksi, radiasi dapat mengionisasi ataudapat pula mengeksitasi atom . Setiap terjadi prosesionisasi atau eksitasi , radiasi akan kehilangansebagian energinya. Energi radiasi yang hilang

akan menyebabkan peningkatan temperatur(panas) pada bahan (atom) yang berinteraksidengan radiasi tersebut.
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CONTINUE..

semua energi radiasi yang terserap di jaringanbiologis akan muncul sebagai panas melaluipeningkatan vibrasi (getaran) atom dan struktur

molekul . Ini merupakan awal dari perubahan kimiawi yang

kemudian dapat mengakibatkan efek biologisyang merugikan.
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jaringan biologis adalah sel. Sel mempunyai inti sel yang merupakan pusat pengontrol sel. Sel terdiridari 80% air dan 20% senyawa biologis kompleks.

Jika radiasi pengion menembus jaringan, makadapat mengakibatkan terjadinya ionisasi danmenghasilkan radikal bebas , misalnya radikalbebas hidroksil (OH), yang terdiri dari atom oksigendan atom hidrogen. Secara kimia, radikal bebassangat reaktif dan dapat mengubah molekul-molekul penting dalam sel.
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CONTINUE.

ada dua cara bagaimana radiasi dapatmengakibatkan kerusakan pada sel.

Pertama, radiasi dapat mengionisasi langsung molekulDNA sehingga terjadi perubahan kimiawi pada DNA.Kedua, perubahan kimiawi pada DNA terjadi secaratidak langsung, yaitu jika DNA berinteraksi denganradikal bebas hidroksil. Terjadinya perubahan kimiawi

pada DNA tersebut, baik secara langsung maupun tidaklangsung, dapat menyebabkan efek biologis yangmerugikan, misalnya timbulnya kanker maupun kelainangenetik.


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Efek radiasi terhadap tubuh manusia bergantung padaseberapa banyak dosis yang diberikan, dan bergantungpula pada lajunya; apakah diberikan secara akut(dalam jangka waktu seketika) atau secara gradual(sedikit demi sedikit).

radiasi gamma dengan dosis 2 Sv (200 rem) yangdiberikan pada seluruh tubuh dalam waktu 30 menitakan menyebabkan pusing dan muntah-muntah padabeberapa persen manusia yang terkena dosis tersebut,

dan kemungkinan satu persen akan meninggal dalamwaktu satu atau dua bulan kemudian. Untuk dosis yangsama tetapi diberikan dalam rentang waktu satu bulanatau lebih, efek sindroma radiasi akut tersebut tidakterjadi.
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Contoh lain, dosis radiasi akut sebesar 3,5 4 Sv(350 400 rem) yang diberikan seluruh tubuh akan

menyebabkan kematian sekitar 50% dari mereka

yang mendapat radiasi dalam waktu 30 harikemudian. Sebaliknya, dosis yang sama yangdiberikan secara merata dalam waktu satu tahuntidak menimbulkan akibat yang sama.


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Selain bergantung pada jumlah dan laju dosis,setiap organ tubuh mempunyai kepekaan yangberlainan terhadap radiasi, sehingga efek yang

ditimbulkan radiasi juga akan berbeda.


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EFEK RADIASI


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CELL PHONE.