GoalDistinguish and illustrate the terms physical body, system of bodies, physical phenomenon, physical law and observation.
New words
physical body · fizik jismsystem of bodies · jismlar sistemasiphysical law · fizik qonunobservation · kuzatish
Explanation
Every object in nature is called a physical body: the Sun, a stone, a tree, a desk, a pencil. The material a body is made of is called a substance: a pencil is a body, its graphite or wood is a substance. If several bodies behave like one body, we call them a system of bodies: a car consists of many parts but moves as a whole. In a physical phenomenon the particles that make up the substance do not change: when water boils or freezes its particles do not turn into another substance (when paper burns a new substance forms — that is a chemical phenomenon). A physical law is a rule expressing a quantitative relation between quantities that describe a phenomenon. Laws are found by observing phenomena and doing experiments; observation means studying a phenomenon without influencing it.
Worked examples
A desk is a body, wood is a substance; a ship is a body, steel is a substance; a car is a system of bodies.
Physical phenomena: a stone falling, a wheel turning, water boiling, light from a bulb. In all of them the particles of the substance stay the same.
Class activity
“Body or substance?”: the teacher calls out words (copper, coin, glass, tumbler, air, balloon). Students stand up for a “body” and stay seated for a “substance”.
Practice
1
Explain the difference between a body and a substance using a spade as an example.
A spade is a body; the steel it is made of is the substance.
2
Which is a physical phenomenon: water freezing or paper burning?
Water freezing — the particles do not change; burning paper is a chemical phenomenon.
3
What is meant by observation?
Studying a phenomenon without influencing it.
4
Why can a train be regarded as a system of bodies?
Because although its carriages and locomotive are separate bodies, they move as a whole.