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This blog is officially opened in 21 August 2009




-10 Recent Posts-
P4 Science Chapter 6: Energy & Light
P4 Science Chapter 5: Circulatory System
P4 Science: Air & the Respiratory System
P4 Chapter 3: The Water Cycle & Importance of Water
P4 Chapter 2: Water and Changes of States
P4 chapter 1: Matter & its 3 states
P3 Science Chapter 1: Diversity
P3 Science Chapter 7: Life Cycles Of Animals
P3 Science Chapter 8: Life Cycle Of Plants
P3 Science Chapter 9: Heredity


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Tuesday, August 25, 2009
P4 Science chapter 7: Heat @ 7:11 PM

P4 Science chapter 7: Heat

1) Source of Heat: Fuels, Sun, Electricity, Friction

2) Temperature is the measure of degree of hotness/ coldness of matter. Thermometers are use.

3) Clinical thermometers are filled w/ mercury. When heat is present, mercury expands and the level rises. A bend near the bulb, a.k.a. constriction , prevents the mercury from falling back.

4) Heat always flows from a hooter object to a colder object. Eventually, the objects will have a same temperature.

5) Good conductors of heat: silver, steel, gold, aluminium, mercury, iron, lead, copper
Non-conductors of heat: Air, Cotton, Wood, Rubber, water, ice, plastic

5) Things expand when heated. When cooled, they contract.
  • Expansion Gaps: Railways tracks have gaps so that when there's heat, there's space for expansion. (We all know that SG is a SUPER HOT country)
  • Air Space in containers ( When the containers says 500ml and they only gives you 495ml, I'm like what the hell?! When you complain, they'll claim its for expansion)
Transfer of thermal energy
We have learnt that heat flows from a region of a higher temperature to a region of a lower temperature. There are 3 different ways in which heat is transferred - radiation, conduction and convection.

Radiation

In radiation, thermal energy is directly transferred without traveling through other substances. This means that it can travel even if no air is present. It is the release of thermal energy from the surface of most bodies and transmitted from place to place directly. The energy from the Sun reaches the Earth by radiation.

Conduction

Conduction is the transfer for heat energy between particles that are close to each other. It involves that flow of hear in the from of kinetic energy from one particle to the other particles around it. It can occur in solids, liquids and gases. Different materials conduct heat at different speeds. (They are classified into conductors and insulators)

Convection
Let's take a kettle with water filled in it as an example.
  1. Heat from the flames is transferred through the metal base of the kettle by conduction.
  2. Water at the bottom of the kettle is heated. The water here expands. This make it less dense that the surrounding water.
  3. Water that is less dense rises.
  4. The cooler water at the top, being denser, sinks to the bottom of the kettle.
  5. This movement of water sets up convection currents.
* Hot air rises, cool air sinks

YAY!! WE ARE DONE WITH P4. ARE YOU READY FOR A TEST?



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