effects of heat

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P3/4 science

Whentheset-upisplacedinabasinoficedwater,theairinsidetheflaskcontractsandtheinklevelgoes down to below its original level.

Method 2

Putting a dented ping pong ball into a beaker of hot water makes it regain its original shape. The heat from the water causes the air inside the ping pong ball to expand and push against its internal sides until it is round again.

reducing the impact of expansion and contraction

Overhead telephone cables are hung loosely. This is so that during cold weather when the cables contract, they will not be pulled so tightly that they snap.

Loosely hung telephone cables allow for expansion and contraction.

Railway tracks have gaps between them to allow for expansion during hot weather or when the tracks gain heat from the train engine. This prevents the tracks from buckling under the intense heat and creating cracks which may cause the train to derail.

The railway tracks buckle up when there is no room for expansion during a hot day.

hot water

railway tracks buckle up

Taken from ScieNce PartNer: a complete Guide to Lower Block Science

Effects Of Heat

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P3/4 science

Concrete slabs laid on the ground have gaps between them for the same reasons.

Concrete slabs found in parking lots

changes in States of Matter

There are three states of matter – solid, liquid and gas.

Matter can change from one state to another by gaining or losing heat.

Matter and changes of state

concrete slab

gap

liquid

solid

Freezingliquid → solid

When a liquid loses heat, it freezes to become a solid.

Meltingsolid → liquid

When solid ice at 0°C is heated, it gains heat and melts to form liquid water.

condensationgas → liquid

When a gas loses heat, it condenses to form liquid water.

evaporation liquid → gas

When a liquid gains heat, it evaporates to form a gas. Evaporation can take place at any temperature above melting point, but the higher the temperature, the faster the rate of evaporation.

gas


Effects Of Heat

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P3/4 science

Matter can change from one state to another by heating or cooling it.

Matter and changes of state

conduction of heat

Heat can flow through matter.

However,heatcanflowmoreeasilythroughsomematerialsthanothers.

Good conductors of heat

Good conductors of heat are materials which allow heat to pass through them quickly and easily.

Metals such as gold, silver, copper etc. are good conductors of heat.

As heat passes through them quickly, good conductors of heat become hot very quickly when heated. This is why cooking utensils are usually made of metal. Heat quickly passes through the pot to cook the food inside it.

Good conductors of heat are usually also good conductors of electricity, i.e. they allow electricity to pass through them quickly and easily. This is why electrical wires are made of copper.

Poor conductors of heat

Poor conductors of heat (or insulators) are materials which do not allow heat to pass through them quickly and easily.

Non-metals such as wood, plastic, styrofoam and rubber are poor conductors of heat.

As heat passes through them very slowly, poor conductors of heat remain relatively cool for a longer time when heated. This is why the handles of cooking utensils are usually made of plastic or wood. We will not get burnt when we touch them.

Gain heat

condensation

evaporationmelting

freezing

sublimation

Lose heat (cooling)

solid liquid gas


Effects Of Heat

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P3/4 science

Magnets come in different shapes and sizes.

Some types of magnets

Natural magnets can be found buried in the ground. They are called lodestones and are made of a material known as magnetite. However, lodestones are rare.

Most magnets are man-made from magnetic materials — iron, steel, cobalt or nickel.

Only magnetic materials can be made into magnets and be attracted by other magnets.

If you bring a magnet close to an object made of a magnetic material, the object will ‘stick’ to the magnet, i.e. it will be attracted to the magnet.

Attraction occurs between a magnet and a magnetic material.

lodestone(natural magnet)

ring magnet bar magnet horseshoe magnet

U-shapedmagnetrod magnetbutton magnet

N

N

N

S

SN

N

SS

SN

A nickel coin is attracted to the magnet.

Smagnet N S


Magnets And Their Properties

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P3/4 science

1. Study the two life cycles shown below.

(a) Apart from the number of stages in their life cycles, deduce a key difference between ananimal which undergoes life cycle A and one which undergoes life cycle B. [1m]

(b) Which group of animals mainly undergoes life cycle A? [1m]

(c) Name two members of the group you mentioned in (b) which are exceptions (that is,they do not undergo life cycle A). [1m]

(d) With reference to life cycle B, what would stage 2 be called if the life cycle was that of[2m]

(i) a cockroach?

(ii) a toad?

(iii) a chicken?

(iv) afloweringplant?

stage 1 stage 2stage 1 stage 2

stage 3Life cycle A Life cycle B

Life Cycles

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Taken from ScieNce ProceSS SkiLLS LoWer BLock 3/4


P3/4 science

(e) In the space below, draw the life cycle of an animal which has one more stage than lifecycle B. (Only the name of each stage is required. You do not need to draw the animal ateach stage.) [1m]

Life cycle C

(f) What is moulting? [1m]

(g) What will happen to the creature if it does not undergo moulting? [2m]

(h) At which stage of life cycle C does the animal undergo the process of moulting? [1m]

Life Cycles

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Answers: 1. (a) An animal which undergoes life cycle A gives birth to its young alive while an animal which undergoes life cycle B lays eggs. 1. (b) The group is mammals. 1. (c) They are the platypus and the spiny anteater. 1. (d) (i) cockroach nymph (ii) tadpole (iii) chick (iv) seedling1. (e)

adult

egg

larva

pupa

1. (f) Moulting is the process where the animal sheds its existing skin and replaces it with a new one. 1. (g) If a creature does notmoult,itwillnotbeabletofitinsideitsoldskinasitgrowsbigger. This is because for creatures which undergo moulting, their existing skin does not grow as they increase in size. 1. (h) It undergoes the process of moulting at the larval stage.



P3/4 science

1. (a) In the space below, draw the life cycle of a cockroach. (Only the name of each stage isrequired. You do not need to draw the animal at each stage.) [1m]

(b) State two similarities between the adult cockroach and its young. [2m]

•

•

(c) State two differences between the adult cockroach and its young. [2m]

•

•

(d) Name another two animals which follow a similar life cycle as the cockroach. [1m]

(e) The cockroach is a common household pest which can spread diseases. How does thecockroach spread diseases? [2m]

Life Cycles

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P3/4 science

The graph below shows the number of cockroaches in an area over a period of time.

(f) Describethechangeinthenumberofcockroachesoveraperiodoffiveweeks. [1m]

(g) What could have caused the change in the number of cockroaches in the 4th week?[1m]

Number of cockroaches

Number of weeks0 1 2 3 4 5

Life Cycles

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Answers: 1. (a)

adult cockroach

(in egg case)

nymph

1. (b) • Both have six legs. • Both have a pair of feelers/a segmented body. (Accept any other reasonable answers.)1. (c) • The adult cockroach has wings but its young does not. • The adult cockroach is bigger in size than its young. (Accept any other reasonable answers.)1.(d)Theyarethedragonflyandthedamselfly.(Accept any other reasonable answers.)

1. (e) When the cockroach goes to a dirty place such as a rubbish dump, germs and dirt particles get stuck to its hairy legs. When the cockroach visits a home or lands itself on food, the germs and dirt particles get rubbed off onto the surface it lands on. A person who comes into contact with the germs may get sick as a result. 1.(f)Thenumberofcockroachesremainsconstantforthefirstfour weeks before decreasing sharply until none of them are left in week 5. 1. (g) An effective pesticide could have been used to spray over the area that the cockroaches were at the start of week 4, causing all of them to get poisoned and eventually die. (Accept any other reasonable answers.)


effects of heat

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