你的繪畫凌亂著 在這個時刻
我想起噴泉旁的白鴿 甜蜜散落了
情緒莫名的拉扯 我還愛你呢
伴你斷斷續續唱著歌 假裝沒事了
時間過了走了 愛情面臨選擇
你冷了倦了 我哭了
一開始的不快樂 你用卡片細寫著
有些愛只給到這 真的痛了
怎麼了 你累了 說好的 幸福呢
我懂了 不說了 愛淡了 夢淹了
開心與不開心 一一細數著 你在不捨
那些愛過的感覺都太深刻 我都還記得
你不等了 說好的 幸福呢
我錯了 淚乾了 放手了 後悔了
只是回憶的音樂盒還旋轉著 要怎麼停呢
怎麼了 你累了 說好的 幸福呢
我懂了 不說了 愛淡了 夢淹了 我都還記得
你不等了 說好的 幸福呢
我錯了 淚乾了 放手了 後悔了
只是回憶的音樂盒還旋轉著 要怎麼停呢
Thursday, August 11, 2011
SPEED
- The speed of an object is the magnitude of its velocity .
- Speed of light is 3*10^8m/s
- Speed is the rate of motion , change , or activities
Wednesday, August 10, 2011
DENSITY [PHYSICS ]
The mass density or density of a material is defined as its mass per unit volume .
Less dense fluids float on more dense fluids if they do not mix. This concept can be extended, with some care, to less dense solids floating on more dense fluids. If the average density (including any air below the waterline) of an object is less than water (1000 kg/m3) it will float in water and if it is more than water's it will sink in water.
The mass density of a material varies with temperature and pressure. (The variance is typically small for solids and liquids and much greater for gasses.) Increasing the pressure on an object decreases the volume of the object and therefore increase its density. Increasing the temperature of a substance (with some exceptions) decreases its density by increasing the volume of that substance. In most materials, heating the bottom of a fluid results in convection of the heat from bottom to top of the fluid due to the decrease of the density of the heated fluid. This causes it to rise relative to more dense unheated material.
We can calculate density using the formula:
Density= Mass/Volume
Less dense fluids float on more dense fluids if they do not mix. This concept can be extended, with some care, to less dense solids floating on more dense fluids. If the average density (including any air below the waterline) of an object is less than water (1000 kg/m3) it will float in water and if it is more than water's it will sink in water.
The mass density of a material varies with temperature and pressure. (The variance is typically small for solids and liquids and much greater for gasses.) Increasing the pressure on an object decreases the volume of the object and therefore increase its density. Increasing the temperature of a substance (with some exceptions) decreases its density by increasing the volume of that substance. In most materials, heating the bottom of a fluid results in convection of the heat from bottom to top of the fluid due to the decrease of the density of the heated fluid. This causes it to rise relative to more dense unheated material.
We can calculate density using the formula:
Effect of heat
1. Thermal expansion of solids
-Most solids expand when they are heated. The expansion is so little that it cannot be noticed normally. Heating a solid causes increased vibration of the molecules, thus the solid expand. Heating a solid makes its molecules vibrate more vigorously. As the vibration become larger, the molecules are pushed further apart and solid expands slightly in all directions.
2. Thermal expansion of liquids
-Almost all the liquids expands when heated. Like solids, most liquids expand when they are heated. But there are exceptions.
-When liquid expand, it is the increase in volume which has to be considered. Since liquids doesn't have a fixed shape we cannot consider its expansion by length. In general liquids expand more than solids. Different liquids expand by different amounts for the same rise in temperature. This property of the liquids is used in construction of various type of thermometers.
-Whenever liquid is stored in a closed container, an air space must be left for expansion to take place. Car radiator systems have space in them for the coolant to expand, and bottles containing liquids are never completely full when you buy them.
3. Thermal expansion of gases
-Gases expand more than solids and liquids when heated. Gases contain independant particles in random motion. They move faster and faster when the temperature rises. This expands the gases the most. Thermal expansion and contraction in a gas cause its density to change. An increase in the volume of a fixed mass of gas reduces its density. A hot air balloon will rise because the air inside it is heated by a flame and expands. The air become less dense than the surrounding cooler air and the balloon rises. It will fall when the air inside it is cooled.
4. Effects of expansion and contraction
-On expansion, the volume of a substance increases. However, the mass of the substance remain the same. Therefore, the increase in volume will decrease the density. On expansion, density of the heated substance decrease. On contraction, the volume of the substance decreases so the density increases. So on cooling the substance increases the density.
-Substances expand when heated, and very large forces may be setup if there is an obstruction to the free movement of the expanding or contracting bodies. Even through the expansion of solids are not visible, it can produce enough force to crack concrete or buckle steel. And it all happen because vibrating molecules need room to move. When water changes into ice, its volume is increased by 9% which is why water pipes burst if they freezes up.
-Solids don't expand much when heated, but the force produced by the expansion can be very high. Concrete and steel beams used in construction work can cause considerable damage if they do not have space to expand when the temperature rises.
5. Useful applications of thermal expansion
-Rivets are steel bolts used to fasten steel plates firmly together.
-A bimetallic strip is made of two strips of different metals joined together. When heated, one metal(Usually brass) expands more than the other(Usually iron) Consequently, the strip bends and a curve strip is obtained. When cooled, the strip bends the other way.
-Bimetal thermostat is a device which used bimetallic strip to keeps temperature constant in electrical appliances.
-Fire alarms make use of the bimetallic strip to close an circuit and trigger an alarm.
-Flashing indicators make use of the bimetallic strip to close and open an circuit to make a light flash according to the opening and closing of the contacts.
6. Thermometers
-Temperature is a measure of the hotness or coldness of a object. Thermometers are instruments used for measuring temperature. Any physical property of a material that changes with temperature can be used to measure temperature. There are different kinds of thermometer used for various purposes.
-The different thermometers are: liquid-in glass thermometer(Mercury and Alcohol type), clinical thermometer, bimetallic thermometer, thermocouple thermometer and resistance thermometer.
-Most solids expand when they are heated. The expansion is so little that it cannot be noticed normally. Heating a solid causes increased vibration of the molecules, thus the solid expand. Heating a solid makes its molecules vibrate more vigorously. As the vibration become larger, the molecules are pushed further apart and solid expands slightly in all directions.
2. Thermal expansion of liquids
-Almost all the liquids expands when heated. Like solids, most liquids expand when they are heated. But there are exceptions.
-When liquid expand, it is the increase in volume which has to be considered. Since liquids doesn't have a fixed shape we cannot consider its expansion by length. In general liquids expand more than solids. Different liquids expand by different amounts for the same rise in temperature. This property of the liquids is used in construction of various type of thermometers.
-Whenever liquid is stored in a closed container, an air space must be left for expansion to take place. Car radiator systems have space in them for the coolant to expand, and bottles containing liquids are never completely full when you buy them.
3. Thermal expansion of gases
-Gases expand more than solids and liquids when heated. Gases contain independant particles in random motion. They move faster and faster when the temperature rises. This expands the gases the most. Thermal expansion and contraction in a gas cause its density to change. An increase in the volume of a fixed mass of gas reduces its density. A hot air balloon will rise because the air inside it is heated by a flame and expands. The air become less dense than the surrounding cooler air and the balloon rises. It will fall when the air inside it is cooled.
4. Effects of expansion and contraction
-On expansion, the volume of a substance increases. However, the mass of the substance remain the same. Therefore, the increase in volume will decrease the density. On expansion, density of the heated substance decrease. On contraction, the volume of the substance decreases so the density increases. So on cooling the substance increases the density.
-Substances expand when heated, and very large forces may be setup if there is an obstruction to the free movement of the expanding or contracting bodies. Even through the expansion of solids are not visible, it can produce enough force to crack concrete or buckle steel. And it all happen because vibrating molecules need room to move. When water changes into ice, its volume is increased by 9% which is why water pipes burst if they freezes up.
-Solids don't expand much when heated, but the force produced by the expansion can be very high. Concrete and steel beams used in construction work can cause considerable damage if they do not have space to expand when the temperature rises.
5. Useful applications of thermal expansion
-Rivets are steel bolts used to fasten steel plates firmly together.
-A bimetallic strip is made of two strips of different metals joined together. When heated, one metal(Usually brass) expands more than the other(Usually iron) Consequently, the strip bends and a curve strip is obtained. When cooled, the strip bends the other way.
-Bimetal thermostat is a device which used bimetallic strip to keeps temperature constant in electrical appliances.
-Fire alarms make use of the bimetallic strip to close an circuit and trigger an alarm.
-Flashing indicators make use of the bimetallic strip to close and open an circuit to make a light flash according to the opening and closing of the contacts.
6. Thermometers
-Temperature is a measure of the hotness or coldness of a object. Thermometers are instruments used for measuring temperature. Any physical property of a material that changes with temperature can be used to measure temperature. There are different kinds of thermometer used for various purposes.
-The different thermometers are: liquid-in glass thermometer(Mercury and Alcohol type), clinical thermometer, bimetallic thermometer, thermocouple thermometer and resistance thermometer.
Tuesday, August 9, 2011
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