Help me F.2 IS ！！10點

1.Fire triangle
圖片參考：http://bits.wikimedia.org/skins-1.5/common/images/magnify-clip.png
The fire triangle.Fire is the result of
combustion
, a rapid reaction between oxygen and a
substance called a fuel. A
fuel
is a material that releases energy when it
burns. Some fuels include oil, coal, wood, gasoline, and paper. Combustion
of these types of fuel always produces carbon dioxide and water. When fuels
don’s burn completely, products such as smoke and poisonous gases may be
produced.
The following three things are necessary to start and maintain a fire—
fuel, oxygen, and heat.
Oxygen comes from the air. About 20 percent of the
air around you is composed of oxygen gas. A large fire creates a draft and
draws oxygen toward it. Fuel and oxygen can be together, but they won’t
react until something provides enough activation energy to start
combustion. This energy can come from a lighted match, an electric spark,
or the heat from a stove. Once combustion starts, the heat released supplies
more activation energy to keep the reaction going.
You can control a fire by removing one part of the fire triangle. You can
control a fire if you can get the fuel away from the flames, keep oxygen from
getting to the fuel, or cool the combustion reaction. Firefighters use large
hoses to spray huge amounts of water on the flaming parts of a building.
Water removes two parts of the fire triangle. Water covers the fuel, which
keeps it from coming into contact with oxygen. Evaporation of the water
uses a large amount of heat, causing the fire to cool.

2.(i) a wet towel.The main effect of a wet towelis is cooling down the fire by absorption of heat energy either at the fuel surface ,

.(ii) The oil floats on the water since it is less dense, and this provides some opportunity to clean up the oil spills by skimming the oil from the surface of the water.

1. the three components in fire triangles are things needed for a fire to be sustained. they're Heat, Oxygen and Fuel.

2i. wet towel - cover the pan with the towel (without touching the oil). by covering it, fresh air (oxygen) cannot enter the flame, such that the fire cannot be sustained.
less importantly, when water in the wet towel vaporises, heat is removed. this cools down the pan, thus may remove the "heat" component in the fire triangle.

2ii. oil is less dense than water. when water is added, water sinks and oil floats. none of the components in fire triangle is removed: oil can still contact fresh air, fuel (oil) is still here, and heat... ↓

water boils at 100 degrees Celsius, while the flame is over 100 degrees without doubt. water will immediately boil under the oil, producing steam. the steam will splash 飛濺 the burning hot oil, which is very dangerous.

more dangerously, since the splashed oil droplets contact with more oxygen, it'll burn more vigorously 劇烈地, causing a bigger fire or even explosion.


2010-09-21 21:41:50 補充：
2ii 係問"點解唔可以用水", 唔係落水"畢"走面頭層油.
你有冇見過用水救呢種火會點樣? 去片!
http://www.youtube.com/watch?v=z7JzJlgNuU8
唔識唔好亂答, 走走走!