Matter
Matter is the word used to described what things or objects are made of. Matter can be solid, liquid or gaseous. Energy is that which causes things to happen. As an example, electrical energy causes an electric motor to turn, which can cause a weight to be moved, or lifted.
1.1.1 Si units
As more and more ‘happenings’ have been studied, the subject of physics has grown, and physical laws have become established, usually being expressed in terms of mathematical formula, and graphs. Physical laws are based on the basic quantities – length, mass and time,together with temperature and electrical current. Physical laws also involve other quantities which are derived from the basic quantities. What are these units? Over the years, different nations have derived their own units (e.g. inches, pounds, minutes or centimetres, grams and seconds), but an International System is now generally used – the SI system.
The SI system is based on the metre (m), kilogram (kg) and second (s) system.
1.1.2 Base Units
To understand what is meant by the term derived quantities or units consider these examples; Area is calculated by multiplying a length by another length, so the derived unit of area is metre2 (m2). Speed is calculated by dividing distance (length) by time , so the derived unit is metre/second (m/s). Acceleration is change of speed divided by time, so the derived unit is:
Some examples are given below:
Basic SI Units
Length (L) Metre (m)
Mass (m) Kilogram (kg)
Time (t) Second (s)
Temperature;
Celsius (q) Degree Celsius (ºC)
Kelvin (T) Kelvin (K)
Electric Current (I) Ampere (A)
Derived SI Units
Area (A) Square Metre (m2)
Volume (V) Cubic Metre (m3)
Density (r) Kg / Cubic Metre (kg/m3)
Velocity (V) Metre per second (m/s)
Acceleration (a) Metre per second per second (m/s2)
Momentum Kg metre per second (kg.m/s)
1.1.3 Derived Units
Some physical quantities have derived units which become rather complicated, and so are replaced with simple units created specifically to represent the physical quantity. For example, force is mass multiplied by acceleration, which is logically kgm/s2 (kilogram metre per second per second), but this is replaced by the Newton (N).
Examples are:
Force (F) Newton (N)
Pressure (p) Pascal (Pa)
Energy (E) Joule (J)
Work (W) Joule (J)
Power (P) Watt (w)
Frequency (f) Hertz (Hz)
Note also that to avoid very large or small numbers, multiples or sub-multiples are often used. For example;
1,000,000 = 106 is replaced by ‘mega’ (M)
1,000 = 103 is replaced by ‘kilo’ (k)
1/1000 = 10-3 is replaced by ‘milli’ (m)
1/1000,000 = 10-6 is replaced by ‘micro’ (m)
1.1.4 MATTER AND ENERGY
By definition, matter is anything that occupies space and has mass. Therefore, the air, water and food you need to live, as well as the aircraft you will maintain are all forms of matter. The Law of Conservation states that matter cannot be created or destroyed. You can, however, change the characteristics of matter. When matter changes state, energy, which is the ability of matter to do work, can be extracted. For example, as coal is burned, it changes from a solid to a combustible gas, which produces heat energy.
| CHEMICAL NATURE OF MATTER In order to better understand the characteristics of matter, it is typically broken down to smaller units. The smallest part of an element that can exist chemically is the atom. The three subatomic particles that form atoms are protons, neutrons and electrons. The positively charged protons and neutrally charged neutrons coexist in an atom’s nucleus | |
The negatively charged electrons orbit around the nucleus in orderly rings or shells. The hydrogen atom is the simplest atom, It has one proton in the nucleus, and one electron. A slightly more complex atom is that of oxygen which contains eight protons and eight neutrons in the nucleus and has eight electrons orbiting around the nucleus.
There are currently 111 known elements or atoms.
Each has an identifiable number of protons, neutrons and electrons. In addition, every atom has its own atomic number, as well as its own atomic mass. The atomic number is calculated by the element’s number of protons and the atomic mass by its number of ‘nucleons’, (protons and neutrons combined).
| 1 H 1.00 | Atomic Number Element Symbol Atomic Mass | ||||||||
| 3 Li 6.94 | 4 Be 9.01 | ||||||||
| 11 Na 22.9 | 12 Mg 24.3 | ||||||||
| 19 K 39.0 | 20 Ca 40.0 | 21 Sc 44.9 | 22 Ti 47.8 | 23 V 50.9 | 24 Cr 52.9 | 25 Mn 54.9 | 26 Fe 55.8 | 27 Co 58.9 | |
| 37 Rb 85.4 | 38 Sr 87.6 | 39 Y 88.9 | 40 Zr 91.2 | 41 Nb 92.9 | 42 Mo 95.9 | 43 Tc 98.0 | 44 Ru 101.1 | 45 Rh 102.9 | |
Fig 2.2 Part of the Periodic Table
1.1.5 Molecules
Generally, when atoms bond together, they form a molecule. However, there are a few molecules that exist as single atoms. Two examples that are used during aircraft maintenance are helium and argon. All other molecules are made up of two or more atoms. For example, water (H2O) is made up of two atoms of hydrogen and one atom of oxygen.
When atoms bond together to form a molecule they share electrons. In the example of H2O, the oxygen atom has six electrons in the outer (or valence) shell.
However, there is room for eight electrons. Therefore, one oxygen atom can combine with two hydrogen atoms by sharing the single electron from each hydrogen atom.
Fig 2.3 Water (H2O) Atom
1.1.6 Physical Nature of Matter
Matter is composed of several molecules. The molecule is the smallest unit of substance that exhibits the physical and chemical properties of the substance. Furthermore, all molecules of a particular substance are exactly alike and unique to that substance.
Matter may only exist in one of three physical states, solid, liquid and gas. A physical state refers to the physical condition of a compound and has no affect on a compound’s chemical structure. In other words, ice water and steam are all H2O, and the same type of matter appears in all these states.
All atoms and molecules in matter are constantly in motion. This motion is caused by the heat energy in the material. The degree of motion determines the physical state of the matter.
1.2 States
1.2.1 Solid
A solid has a definite volume and shape, and is independent of its container. For example, a rock that is put into a jar does not reshape itself to form to the jar. In a solid there is very little heat energy and, therefore, the molecules or atoms cannot move very far from their relative position. For this reason, a solid is incompressible.
1.2.2 Liquid
When heat energy is added to solid matter, the molecular movement increases. This causes the molecules to overcome their rigid shape. When a material changes from a solid to a liquid, the material’s volume does not significantly change. However, the material will conform to the shape of the container it is held in. An example of this is a melting ice cube.
Liquids are also considered incompressible. Although the molecules of a liquid are further apart than those of a solid, they are still not far enough apart to make compression possible.
In
a liquid, the molecules still partially bond together. This bonding force is
known as surface tension and prevents liquids from expanding and spreading out
in all directions. Surface tension is
evident when a container is slightly over filled.
FIGURE 2.4 – OVERFILLED CONTAINER
1.2.3 Gas
As heat energy is continually added to a material, the molecular movement increases further until the liquid reaches a point where surface tension can no longer hold the molecules in place. At this point, the molecules escape as gas or vapour. The amount of heat required to change a liquid to a gas varies with different liquids and the amount of pressure a liquid is under. For example, at a pressure that is lower than atmospheric, water boils at a temperature lower than 100º C. Therefore, the boiling point of a liquid is said to vary directly with pressure.
Gas differs from solids and liquids in the fact that they have neither definite shape nor definite volume. Chemically, the molecules in a gas are exactly the same as they were in their solid or liquid state. However, because the molecules in a gas are spread out, gasses are compressible.