الأسبوع 11 · المحور الثاني «المادة والطاقة»، الوحدة الثانية «حركة الجسيمات»، المفهوم 2.2 «وصف المادة وطرق قياسها» (ب) والمفهوم 2.3 «مقارنة تغيرات المادة» (أ): الخصائص المفيدة وبداية التغيرات · 3 دروس
1
The right material for the job
Discovery Education Science P5: Term 1, Unit 2, pp. 163–166
GoalChoose the right tool and unit to compare materials, and explain why a property makes a material useful.
New words
measure · to find out how much, how long or how big something is, using a tool and a unitproperty · something about a material that we can observe or measure, such as hard or bendyconduct · to let heat or electricity pass through easily
Explanation
To compare materials fairly, we measure them. Mass is how much matter there is, and we measure it with a balance in grams (g). Length is measured with a ruler in centimetres (cm). Volume is how much space something takes up, and we measure it with a measuring jug in millilitres (mL). Choose the tool that matches your question. Measurements also show patterns: a small, heavy stone can have more mass than a big, light sponge. Properties tell us what a material is good for. Copper can be stretched into a thin, bendy wire and it conducts electricity well, so it is used for electric wires. Wood cannot be stretched into wire and does not conduct electricity well, so it is not. Glass is transparent, so it makes windows, and rubber is flexible and waterproof, so it makes boots.
Material
Useful property
Used for
copper
bends into wire, conducts electricity
electric wires
steel
hard and strong
hammers and spanners
glass
transparent
windows
rubber
flexible and waterproof
boots and tyres
Worked examples
Piece
Mass (g)
Length (cm)
Volume (mL)
A
240
12
50
B
90
30
20
C
160
8
120
Karim measures three pieces of material and writes the results in a table. Piece A has the most mass (240 g), so it has the most matter. Piece B is the longest (30 cm). Piece C takes up the most space (120 mL). Different measurements can pick different winners.
Three things in Omar’s home: a window, a boot and a hammer. Each was made from a material with a property that suits the job: transparent glass, waterproof rubber and hard steel.
Malak wants a bucket to carry water. Paper is light, but it is not waterproof, so it goes soft and leaks. A plastic bucket is waterproof, so it is the better choice.
Class activity
Property detective (a grown-up helps). Choose five objects at home, such as a spoon, a key, a sock, a cup and a pencil. For each one, write the material and the property that makes it good for its job. Then use a kitchen scale to find the mass of two objects in grams, and a ruler to find the length of two objects in centimetres. Write every result with its unit.
Practice
1
Which tool and unit would you use to find the length of a pencil?
A ruler, in centimetres (cm).
2
Look at the table. Which material has the most matter, and which takes up the most space?
Material
Mass (g)
Length (cm)
Volume (mL)
X
120
18
60
Y
200
9
40
Z
75
25
90
Y has the most matter, because its mass is the largest (200 g). Z takes up the most space (90 mL).
3
Why are electric wires made of copper and not of wood?
Copper can be stretched into thin wire and conducts electricity well. Wood cannot be stretched and does not conduct electricity well.
4
Which property of glass makes it good for windows?
It is transparent, so light passes through and we can see outside.
