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What are the effects of adding heat? (3)

1) temperature normally increases
2) almost all substances expand but rate and amount of expansion is different for different substances for the same temperature rise
3) change an object from solid to liquid state&liquid to gaseous state


What are the effects of removing heat?

1) temperature usually decreases
2) almost all substances contract. The rate and amount of contraction differs for different substances for the same temperature drop.
3) change liquid to solid state&gaseous to liquid state


Arrange the three states in ascending order for rate of expansion and contraction. (Slowest to fastest)

Solid, liquid, gas


Why are the walls of glass contains usually thin?

When the pour boiling water too quickly into a cup made of thick flass, the glass may crack as the glass on the inside expands faster than the outside when heated.


What is an effect of expansion&contraction?

Expansion and contraction may cause damage to structures that are constantly exposed to the environment.


List the five examples of effects on expansion&contraction.

1) telephone wires and electricity cables are strung loosely from pole to pole to prevent breakage during contraction in cold weather.
2) expansion gaps between concrete slabs and tiles are laid to provide space for tiles and concrete slabs to expand without damage as excessive expansion can cause concrete to crack and pop out.
3) expansion bends are made in water and oil pipes to allow the pipes to expand without damaging or bursting
4) expansion gaps in tracks provide space for tracks to expand without any bends, twists, and damage.
5) expansion gaps or a free end resting on rollers for metal structures allow them to expand without any damage on hot days.


What are two uses of expansion?

1) opening tight fitting metal lids on jars by immersing it in warm water to let it expand more than the glass jar. This loosens the lid and allows us to unscrew it easily.
2) rivets are used to join steel plates and girders. When red hot, it is placed in position and hammered into a head and allowed to cool. As the rivet cools, it contracts and pulls steel plates together.


How does the movement of heat occur?

Coduction, convection and radiation.


What is conduction?

Conduction is the transfer of heat through a medium or material without any visible movement of the medium or material.


Why do some objects feel colder to touch than others at room temperature?

Some objects are better conductors of heat than others.


How do we experiment the rate of heat flow through different materials?

1) coat rods of different materials with wax.
2) place the rods into rubber bungs and insert them into the side of a metal trough.
3) put hot water into the trough.
4) the rod that has wax that melts the fastest is the best conductor of heat.


What are bad conductors of heat used for and where are they used?

Bad conductors are used to reduce the amount of heat transfer. They are found in walls of buildings and in items such as handles of cooking utensils.


What is convection?

Convection is the transfer of heat in a medium due to the movement of the medium arising from density differences.


In what states do convection usually occur?

Liquid and gases.


Why do convection occur in liquids?

Convection takes place due to the expansion of a fluid. When it is hot, its volume increases and its density decreases. The less dense fluid then rises while dense fluid flows in to take its place.


Explain the process of heating liquids in terms of convection.

The heat supply warms up the liquid at the bottom which expands, becomes less dense and rises. The surrounding water which is cooler and denser will sink to the bottom to be heated up. The cycle repeats itself, setting up convection currents until all the water is heated.


List 3 examples of application of convection.

1) in homes, we use the air conditioner. The air conditioner cools the hot air, which becomes denser and sinks to the bottom of the room. More hot air rises and is cooled by the air conditioner. This cycle repeats itself until the room is cooled.
2) sea breezes - the land absorbs heat from the sun and warms up faster than the sea. The air above the land is heated up and rises. Cooler, denser air above the sea moves in to replace the warm air above the land.
3) land breezes - the land loses heat faster than the sea and cools down faster. Air above the sea is now warmer and rises. Cooler, denser air above the land moves in to replace the warm air above the sea.


What is radiation?

Radiation is the direct transfer of heat in the form of waves, from one place to another without the need for a medium.


What are the 3 factors to determine the rate of radiating and absorbing heat of a body?

1) nature of the surface - the darker and rougher the surface, the higher the rate of radiation or absorption.
2) total surface area of the body - the greater the area, the higher the rate of absorption or radiation.
3) temperature of body - the hotter the body, the higher the rate of radiation.


State 2 uses of good and bad radiators of heat.

1) cooking utensils and kettles are brightly polished to keep their contents hot.
2) heating surfaces of electric stoves are black&the heating coil has a large surface area. These properties make the surfaces excellent radiators of heat.


What is heat?

A form of energy that flows from a hotter region to colder region.