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conduction,convection and radiation

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jasmine garcia

on 17 February 2015

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Transcript of conduction,convection and radiation

conduction,convection and radiation.
ch.
.

part A


figure 22

Conduction
~
Is the transfer of thermal by collisions between particles in matter.
* In solids collusion happen between neighboring particles.
*Particles in solids are packed closely together.
* These particles can slightly move back and forth but they stay in one place.
* This causes for collision to be only possible between particles that are next to each other.
* Conduction can happen in in all material but thermal energy moves faster in certain materials.
~
Conductors
Materials in which thermal energy moves quickly.
* copper is a conductor that is why we make electricity wires out of copper.
Table 1

* There is also materials that make thermal energy run slower than usual,these are called insulators.
* Gasses are good insulators because particles there are so spread out which means collisions accure less often.
figure 23
Part- B
Convection
~
The transfer of thermal energy by the movement of matter from one place to another.
* For convection to be able to happen the particles of the material have to be able to move easily.

* Particles in solids can't move easily this means that fluids are the best option for this job.
Fluid
~
This material is made out of particles that can easily change locations.
* Liquids and gasses are fluids.
Effect
Effect
How thermal energy is transferred by conduction,convection and radiation
~ Big Idea ~
~ Examples ~
~ Insulators ~
1. Air
2. Plastic foam
3. Fiberglass
* During convection parts of the fluid that have a higher tempature move somewhere where the tempature is lower.
* Convection is caused because of the changes in density in a fluid.
* Different items have different densities even a sample of the same item can have a different density.
* Most materials expand or take up more space if the tempature gets hotter.
* The density of an object gets lower if the tempature gets hotter.
Part B Continued
* An object sinks if it's density is greater than the density of the fluid around around.
* And an object will float only if the density of the object is less than the density of the fluid around it.
EX. Hot-air balloons and helium filled balloon
* when a hot-air balloon is in the air the heat from the burner heats up the air in the balloon making the air balloon less dense than the air around it allowing it to float.
* while the balloon is in the air it releases thermal energy so when yhe balloon cools its volume decreases ---> making the density decrease causing the balloon to sink.
* This means convection happens only in liquids and gasses
* It is similar with when fluids are heated the warmer part of the fluid is less dense.
figure 25
*
convection currents
~
The circular motion that results in a fluid heated from below.
Part C
Radiation
~
The transfer of thermal energy trough electromagnetic waves.
* Unlike conduction and convection that can only move in matter radiation can transfer energy trough matter and empty space.
* Radiation can cause thermal energy to be transfered between objects that are not touching.
figure 26
* The lamp gives off electromagnetic waves that travel to the food keeping it warm.
* Another example of radiation happens every day, every day the sun gives off thermal energy that travels trough millions of miles of empty space to reach earth
* The Earth's atmosphere and surface absorves this energy allowing it to be warm enough for us to live.
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