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# Physics Theory : Matter

 Preparation Just what you need to know !

The three states of matter are solid, liquid and gas.

Solids have a definite volume and a definite shape.

Liquids have a definite volume, but no definite shape (because they take the shape of the container in which they are placed).
Liquids can be poured (but solids cannot) because the force of attraction between molecules is less in liquids (than in solids).
Change of state from liquid to solid occurs when there is a fall in temperature.
In fact, the change of state from liquid to solid occurs at a certain constant temperature with heat being released, e.g., water changes to ice at the freezing point of 0oC.

Gases have neither a definite volume nor a definite shape.
Change of state from liquid to gas occurs during evaporation when molecules of the liquid escape from the surface.

Air is a mixture, and not a state of matter.

Atoms typically combine together to form molecules.
Kinetic Theory states that the distances between molecules are greater than their sizes.
An atom usually consists of protons, neutrons and electrons.
Substances which consist of atoms that are alike are called elements.

Elements (113 in number) are systematically arranged in the modern periodic table.
Of the 113 elements, 92 are natural elements.

Hydrogen is the lightest element.
Its atomic number is 1 and its atomic mass is 1.01.

Uranium is the heaviest natural element.
Its atomic number is 92 and its atomic mass is 238.03.

Mass is the amount of matter in a substance.
Mass of a body is a constant (does not vary) and is determined by a beam balance.

Weight of a body is its mass multiplied by gravitational acceleration (W = m g).
Weight of a body from the Earth decreases by a factor of about 6 when taken to the Moon because the gravity on the Moon is about 1/6th that on the Earth.
Weight of a body is determined by a spring balance (where gravity comes into play).

Sir Isaac Newton discovered the Law of Gravitation.
Newton's Universal Law of Gravitation states that the force of attraction F between two bodies is directly proportional to the product of their masses (M and m) and inversely proportional to the square of the distance r between them. Mathematically,
F = G M m / r2,
where G is a proportionality constant called the Universal Gravitation Constant, whose value is 6.67 × 10−11 N m2/kg2.

Johan Kepler formulated the following three Laws of Planetary Motion.
1. All planets move in elliptical orbits with the sun at the focus.
2. The radius vector from the sun to the planet sweeps equal areas in equal time.
3. The square of the time period of a planet is proportional to the cube of the semimajor axis of the ellipse.

Physics Quiz on Matter.

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