☰ Contents · Technology

The metalworking workshop and metals

Lessons 1–4 · 4 lessons · Sh. Sharipov, N. Muslimov, O. Tolipov, Q. Abdullayeva, O. Qo‘ysinov, V. Sattorov, S. Ahmadaliyev, M. Mo‘minova. Mehnat ta’limi (Labour Education / Technology), Grade 5. Sharq Publishing, Tashkent, 2015
4

Appearance and distinguishing features of metals

Textbook: pp. 7–9
GoalLearn to tell metals apart by colour and properties.
New words
lustre · yaltiroqlikmelting point · erish haroratihardness · qattiqlikbrittleness · mo‘rtlik
Explanation

Metals differ in colour: steel is grey, zinc bluish-white, copper reddish. All metals are lustrous to some degree and conduct heat and electricity well. Each metal has its own melting point, at which the solid turns liquid; the melting point of steel is far higher than that of tin. Hardness is a metal’s ability to resist the action of another body: steel is harder than copper. A plastic metal changes shape under force but does not break; cast iron is brittle and breaks when struck by a hammer. These properties must be known before making an item.

Worked examples
A copper pot in the kitchen is told from a steel knife at once by its reddish colour.
A cast-iron plate may crack if dropped because cast iron is brittle; a steel plate can only bend.
Class activity

Sorting samples: the teacher gives metal samples with smoothed edges (steel, copper, aluminium, brass). The group fills a table: colour, lustre, weight, firmness (press gently by hand). Find the steel with a magnet. Do not heat, bend or hit the samples; do not touch any sharp edge.

Practice
1
What colour is copper?
2
Give an example of a brittle metal.
3
Which is harder, steel or copper?
4
Why is a plastic metal convenient for making sheet metal?