Friday, 9 November 2012
HEAT TRANSFER
Energy Likes to Move
If there is a temperature difference in a system, heat will naturally move from high to low temperatures. The place you find the higher temperature is the heat source. The area where the temperature is lower is the heat sink.Ever Hear of Convection Ovens?
Convection is the way heat is transferred from one area to another when there is a "bulk movement of matter." It is the movement of huge amounts of material, taking the heat from one area and placing it in another. Warm air rises and cold air replaces it. The heat has moved. It is the transfer of heat by motion of objects. Convection occurs when an area of hot water rises to the top of a pot and gives off energy. Another example is warm air in the atmosphere rising and giving off energy. They are all examples of convection. The thing to remember is that objects change position.Radiating Energy
When the transfer of energy happens by radiation, there is no conductive medium (such as in space). That lack of medium means there is no matter there for the heat to pass through. Radiation is the energy carried by electromagnetic waves (light).Conducting Energy and Heat
Conduction is a situation where the heat source and heat sink are connected by matter. As we discussed before, the heat flows from the source down the temperature gradient to the sink. It is different from convection because there is no movement of large amounts of matter, and the transfers are through collisions. The source and the sink are connected.
If you touch an ice cream cone, the ice cream heats up because you are a warmer body. If you lie on a hot sidewalk, the energy moves directly to your body by conduction.
http://www.physics4kids.com/files/thermo_transfer.html
MECHANICAL ENERGY
Mechanical energy is the energy which is possessed by an object due to its motion or its stored energy of position. Mechanical energy can be either kinetic energy (energy of motion) or potential energy (stored energy of position). Objects have mechanical energy if they are in motion and/or if they are at some position relative to a zero potential energy position (for example, a brick held at a vertical position above the ground or zero height position).
A moving car possesses mechanical energy due to its motion (kinetic energy). A moving baseball possesses mechanical energy due to both its high speed (kinetic energy) and its vertical position above the ground (gravitational potential energy). A World Civilization book at rest on the top shelf of a locker possesses mechanical energy due to its vertical position above the ground (gravitational potential energy). A barbell lifted high above a weightlifter's head possesses mechanical energy due to its vertical position above the ground (gravitational potential energy). A drawn bow possesses mechanical energy due to its stretched position (elastic potential energy).
An object which possesses mechanical energy is able to do work. In fact, mechanical energy is often defined as the ability to do work. Any object which possesses mechanical energy - whether it be in the form of potential energy or kinetic energy - is able to do work. That is, its mechanical energy enables that object to apply a force to another object in order to cause it to be displaced.
Numerous examples can be given of how an object with mechanical energy can harness that energy in order to apply a force to cause another object to be displaced. A classic example involves the massive wrecking ball of a demolition machine. The wrecking ball is a massive object which is swung backwards to a high position and allowed to swing forward into building structure or other object in order to demolish it. Upon hitting the structure, the wrecking ball applies a force to it in order to cause the wall of the structure to be displaced.
http://www.kids.esdb.bg/mechanical_principles.html
MORE SOUND!
. Sound is energy that is made by vibrations. When any object vibrates it causes movement in the air.
The air particles then bumps into each other and then bump into others. This continued bumping cause
The air particles then bumps into each other and then bump into others. This continued bumping cause
a sound wave.
2. If the human ear is within the range of the vibrations, a sound can be heard.
3. When the vibrations are fast, the sound is high. When the vibrations are slow, the sound is low.
4. Sound waves are also called pressure waves because they move the particles they are passing through.
5. The ear is not the only detector people and animals have. Sound waves can even be felt by different
parts of the body. Sometimes you can feel the vibrations thunder makes while you are actually hearing it.
6. Stringed instruments are played when fingers or a bar are pressed down on the strings. This pressure
changes the strings' length, causing them to vibrate at different frequencies and make different sounds.
Shortening a string makes it sound higher, while lengthening a string can produce a lower sound.
Strings also produce different sounds depending on how thick they are.
7. In wind instruments, there is a reed (a thin piece of wood inside the mouthpiece, that vibrates
when air travels over it. The keys produce different size openings in the instrument. The air columns
inside the instrument are then made shorter or longer which produces different sounds.
8. Sound waves can bend around corners and obstacles.
9. The human ear that is attached to the side of the head acts as a funnel to catch sounds. The inner ears,
eardrums and tiny bones inside the ear called the hammer, anvil and stirrup all begin to vibrate. Sound
vibrations then move through an oval opening called the cochlea. In the cochlea--a snail shell-like,
fluid-filled chamber--the sound waves stimulate tiny hairs that are connected to the auditory nerve.
The auditory nerve receives signals from the nerve cells and transmits them to the auditory center in the brain.
10. The brain receives these messages from the auditory nerve. The messages comes in fast and furious,
in a jumble of confusion, but the brain has the ability to sort them into an organized pattern.
This way we can understand the sounds we hear as music or human speech.
http://www.kidskonnect.com/subjectindex/15-educational/science/88-sound.html
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