Lessons 8–10 · 3 lessons · K. T. Suyarov, Z. B. Sangirova, M. T. Umaraliyeva, S. G‘. Xasanova, M. K. Yuldasheva, D. T. Hasanova. Natural Science, Grade 6 (new edition). Republican Education Centre, 2022
8
Liquids
Textbook, pp. 21–22
GoalList the properties of liquids and tell liquids from free-flowing solids such as sand and powder.
Liquid water covers most of the Earth’s surface. A liquid takes the shape of its container but does not change its volume: pour it from a glass into a flask and then into a measuring cylinder and its shape changes while its volume stays the same. Liquid particles are close together but not packed as tightly as in a solid, and they move around more; so a liquid is hard to compress. The mass of a liquid can be found by weighing it. Not every liquid is water: oil (neft) and mercury are liquids with no water in them. Sand and powder take the shape of a bag and pour when tipped, but each grain is a solid, so they are not liquids.
Worked examples
100 ml of juice is poured from a glass into a bowl. The juice in the bowl is still 100 ml, only its shape is different. So a liquid keeps its volume.
Liquids: water, milk, vegetable oil, honey (flows slowly), mercury (a liquid metal, poisonous!). Sand, sugar and flour are solids even though they pour.
Class activity
Experiment: pour the same 100 ml of water into three differently shaped containers (a glass, a wide saucer, a tall narrow bottle) and measure its volume with a measuring cylinder. Then pour a glass of dry sand the same way and compare: sand forms a heap while water forms a flat surface. Safety: use plastic containers instead of breakable glass and wipe spilt water at once.
Practice
1
What can be said about the shape and volume of a liquid?
Its shape is that of the container; its volume does not change.
2
Name two liquids that do not contain water.
Oil (neft) and mercury.
3
Why is a liquid hard to compress?
Its particles lie close together with little empty space between them.
4
Sand takes the shape of a container and pours. Why is it not a liquid?
Each grain of sand is a solid with its own shape; in a liquid the particles slide freely past one another.