PS RS P4L27 Heat 4 WS_2

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Topic: HEAT 4 (LESSON 27)

Rocket Science | Primary 4

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Primary 4: Rocket Science

Expansion and Cotraction
Expansion and contraction affects our daily life and the things we use.
Telephone wires
When the telephone wires are put up, there are allowances made for
expansion on a hot day and contraction on a cool night. Wires that are put up
tautly will snap on a cold day due to contraction. Wires put up too loosely will
sag too much on a hot day.

Piping system
The piping systems often carry hot fluids, thermal expansion and the
associated stresses must be carefully considered to avoid problems. The
forces created by the thermal expansion can be large enough to cause pipe
bowing and buckling, damaged pumps, valves, pipe clamps and fixings and
even fracturing of the pipe or damage to the steel or concrete structure of the
building.

Primary 4: Rocket Science

Bimetallic strip

A traditional thermostat has two pieces of different metals bolted together to
form what's called a bimetallic strip (or bimetal strip). The strip works as a
bridge in an electrical circuit connected to your heating system. Normally the
"bridge is down", the strip carries electricity through the circuit, and the heating
is on. When the strip gets hot, one of the metals expands more than the other
so the whole strip bends very slightly. Eventually, it bends so much that it
breaks open the circuit. The "bridge is up", the electricity instantly switches off,
the heating cuts out, and the room starts to cool.

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Primary 4: Rocket Science

Railway Lines
Rails are made of steel which expands on heating and contracts on cooling.
A gap is left between two ends of the rails at the joint. If no gaps are left, due
to expansion in hot weather the rails get distorted causing derailment. For the
same reason, gaps are left in the concrete slabs of bridges and highways.

Expansion gap on railway track Buckled railway track

Bridges

The expansion and contraction of materials can also cause problems. For
example, bridges expand in the heat and need special joints to stop them
bending out of shape.
https://www.youtube.com/watch?v=5pKD2McG1PA&list=PLJoJ1sS9GvfgH
OSOc0Ob2T8rIJtVJaxAo&index=4

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Primary 4: Rocket Science

Activity: Hot air expands

You will need:
•Hot water from a kettle or thermos
CAUTION: Adults to use this only!
•A glass bottle
•A balloon
•A tall plastic container

Attach your balloon onto your Place your glass bottle into the
glass bottle. large plastic cup.

Carefully pour the hot water over Keep going until the balloon is
the neck of the glass bottle. You
should see the balloon start to inflated as in the picture!
inflate.
CAUTION: Adults to use this only! Try placing the bottle into cold
water… what happens to the
inflated balloon now?

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Primary 4: Rocket Science

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Primary 4: Rocket Science
1. Dennis wanted to measure the temperature of hot water in a beaker.

Which of the following diagrams shows the correct position of the thermometer
when taking temperature reading?

(1) (2)

(3) (4)

()

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Primary 4: Rocket Science

2. Three friends filled a container with ice cubes and left it on the kitchen table.

ice 5 hours water
cube later

They observed that the ice cubes melted to form water after being left in
room temperature for about five hours and made the following conclusions.

Kerry The heat from the ice cubes causes it to melt.
Larry The ice cubes gain heat from the surrounding air.
Mary The coldness of the ice travel out of the ice cubes.

Who made the correct statement(s) to explain why the ice melted?

(1) Larry only
(2) Kerry and Larry only
(3) Kerry and Mary only
(4) Kerry, Larry and Mary

()

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Primary 4 : Rocket Science
3. The diagram below shows an experiment of an iron ball and an iron ring.

iron ball
iron ring

The iron ball cannot go through the ring. Which one of the following
actions would allow the ball to go through the ring?

A. Cool the ball.
B.Cool the ring. C
Heat the ball. D
Heat the ring.

(1) A and B only
(2) C and D only
(3) B and C only
(4) A and D only

()

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Primary 4 : Rocket Science

4. Dawn was baking some cookies. While she was taking the cookies out
from the oven, he felt that the metal tray was hotter than the cookies.

metal tray

cookie

Which of the following statements best explains her observations above?
(1) The cookies are better conductors than the metal tray.
(2) The metal tray is a better conductor than the cookies.
(3) The metal tray is bigger than the cookies, so it cannot lose heat.
(4) The cookies are left in the oven for a shorter period of time than the tray.

()

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Primary 4 : Rocket Science

5. Sally wanted to know which fabric, X or Y, would be more suitable to make
a sweater. She wrapped one layer of each fabric around two identical cans
as shown below. Then, she poured the same amount of hot water into each
can and covered both with a lid that had a thermometer through its centre.
She observed the set-up below for 30 minutes.

thermometer
lid

XY

What should Sally measure to find out which fabric would be more suitable to
make a sweater to keep her warm?

(1) Temperature of fabric
(2) Amount of water at the end of the experiment
(3) Temperature of water at the end of the experiment
(4) Temperature of water at the start of the experiment

( )

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Primary 4 : Rocket Science
6. A metal rod was bent into the shape as shown.

The metal rod was then heated for 20 minutes.
Which of the following is correct?

mass of metal rod distance between Y and Z
(1) increase increase
(2) increase decrease
(3) remain the same decrease
(4) remain the same increase

( )

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Primary 4 : Rocket Science

7. The diagram below shows four beakers of water. Each beaker contained
different volumes of water at different temperatures. They were left to cool
in an air-conditioned room of 25 oC.

Q R S T

100 cm3 80 cm3 100 cm3 80 cm3
40°C 70°C 70°C 40°C

Which of the following shows the beakers that took the shortest and
longest time to cool?

Shortest time to cool Longest time to cool

(1) T S
(2) R Q
(3) T Q
(4) R S

( )

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Primary 4 : Rocket Science

8. Two containers carrying the same amount of liquid Y at 90ºC were placed in
a basin of water at 25ºC. One container was made of material P while the
other was made of material Q. Material P is a better conductor of heat than
material Q.

container made of material P container made of material Q
liquid Y at
90ºC

basin of
water at
25ºC

Material P
Material Q

Which of the following graphs correctly shows the changes in the
temperature of liquid Y in both containers over a period of time?

Temperature of liquid Y (°C) (2) Temperature of liquid Y (°C)
(1)

Time (min) Time (min)

(3) Temperature of liquid Y (°C) (4) Temperature of liquid Y (°C)

Time (min) Time (min)
()
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Primary 4 : Rocket Science

9. Walking pavements are often covered with concrete blocks with spaces as
shown in the diagram below.

space between
concrete blocks

Why are the spaces between the concrete blocks necessary?
(1) As part of the design of the floor
(2) To allow the blocks to expand during hot weather
(3) To allow plants to grow in the spaces between the blocks
(4) To reduce the amount of light reflected off the walking pavement

()

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Primary 4 : Rocket Science

10. Tanya heated a beaker of water. At certain points in the experiment, she
added a cube of ice into the beaker of water. She measured and recorded
the temperature of the water throughout the experiment and plotted a
graph as shown below.

At which points is the ice added to the beaker?
(1) A and C
(2) B and D
(3) A, B and D
(4) A, C and E

()

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Primary 4 : Rocket Science

Activity 3 – Open-ended Questions
1. The diagram shows a garden bench.

wooden
seat

metal leg

The changes in temperature of the garden is recorded in the table below.

Time 10 a.m 12 p.m 2 p.m 4 p.m 6 p.m
32 30 29
Temperature (oC) 29 31

(a) Predict the temperature of the leg of the bench at 2 p.m. [1]
Explain your answer.

(b) When Jerald sat on the bench at 6 pm, the leg of the bench felt [1]
colder than the seat. Explain why.

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Primary 4 : Rocket Science

(c) Jerald observed the concrete tiles on the garden pathway. Some of the
tiles “popped up” as shown in the diagram below.

“popped up”
garden tiles
What could have caused the tiles to “pop up”? Explain your answer. [1]

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Primary 4 : Rocket Science

2. Alice’s cup of tea was too hot to drink. She decided to cool the tea by
placing the cup in a basin of cold water.

cup of hot basin
tea cold

(95oC)

water

(10oC)

She recorded the temperatures of the tea and water. Her results are
shown in the table below.

Time (minutes) Temperature of tea Temperature of water
(oC) (oC)

2 90 15

4 80 20
6 70 30
8 60 40

10 50 50
12 50 50
14 50 50

(a) Give a reason why the hot tea in the cup became cool. [1]

(b) Alia observed that the temperature of the tea decreased and then [2]
remained constant from the 12th to the 14th minute. Explain why.

(c) What can Alia do to the cold water in order to cool down the tea faster?
[2]

1918

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Primary 4: Rocket Science

Activity 4: Fun facts – Land and Sea Breeze

https://www.youtube.com/watch?v=a82z1DHMdxY 2019
1. What is wind? How is it produced?
2. What causes sea breeze?
3. What causes land breeze?

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