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Properties Of Matter
Density
Density is defined as the mass per unit volume
Density =
mass / volume
ρ
= m/v ( kgm-3 )
- Most substances are denser as a solid than as a liquid, water is an exceptional. Gases have the least density.
- A material is denser at low temperatures than at high temperatures. The number of molecules found in a unit volume becomes smaller when the temperature is high. The mass of the material is the sum of masses of all its molecules.
Pressure
Pressure is defined as the force per unit area. Pressure is a scalar quantity.
P = F/A ( N/m2 or Pa )
Pressure in a Liquid has the following Properties:-
It increases with depth.
At a given point in a liquid the pressure acts equally in all directions.
A liquid can transmit a pressure exerted on it in one place so that it acts at some other place.
Changing The State Of A Substance
Deformation Of Solids
Most objects shows deformation ( change in shape or dimension ) when a force is applied to them. The applied force may act in different directions.
Tension: Forces act outwards in opposite directions & tend to lengthen the body.
Compression: Forces act inwards in opposite directions & tents to shorten the body.
Shear: Forces act in opposite directions along parallel faces, producing a tendency for parallel sections of the body to slide.
Torsion: A type of shearing which twist the body lengthwise ( torque ).
Bending: Due to a moment applied to the body.
In a loaded structure, there are several factors affecting the response of it to a particular applied force or forces. Among these factors are: the type of material, its shape, thickness & density.
Stress = Applied Force/Area = F/A N/m2 or Pa
The size of deformation due to the applied stress depends on the changes appear in the body.
Strain = Change In A Certain Dimensions/Original Dimension
| Name | Stress | Strain | Ratio |
| Tensile | F (perpendicular)/A unit less | ∆l/l unit less |
Young's modulus (E) =
(F(perpendicular)/A)/(∆l/l) |
| Shear | F (parallel)/A N/m2 | x/h unit less | Shear modulus = (F(parallel)/A)/(x/h) |
| Bulk | -∆P | ∆V/V unit less | Bulk Modulus = -(∆P)/(∆V/V) |
Hooke's Law
A stretching force, or tension, applied to a solid tends to pull the atoms or molecules apart. Compressing the solid pushes the atoms or molecules closer to each other. An attractive force between the molecules works in the first case while a repulsive force works in the second case to retain the original intermolecular distance.
To have a very clear change in length, we
may take the extension in springs as a good example. Hooke's
law states that F α
K is called the spring constant, force constant or stiffness. The restoring force acting to retain the original length of the spring is given by F = _ K∆l.
K has the units of force per unit length i.e.: N/m. We can define it as being the force producing on extension equal to unit length.
Springs can be compressed as well as extended. We can think of compression as negative force causing a negative distortion. ( i.e.: reduction of length is negative ).
