MECHANICAL PROPERTIES OF MATTER  
Matter  
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s anything that has mass and occupies space.  
State of Matter  
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State of matter is defined in terms of the phase transitions which indicate  
the change in structure and properties.  
Matter exists in three physical states, namely  
(a) Solid state  
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(b) Liquid state  
(c) Gas (Vapor) state  
Structure of matter  
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Matter is made up of tiny particles.  
The particles are either atoms or molecules  
Atom  
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Is the smallest particle of an element, which can take part in a chemical reaction  
For example, Sodium atom (Na), hydrogen atom (H) etc  
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Molecules  
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A molecule is a group of two or more atoms held together by chemical bonds.  
For example, water molecule (H2O), hydrogen molecules (H2)  
Particulate Nature of matter  
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Matter is made up of millions of tiny particles which cannot be seen with  
naked eyes  
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These particles are called atoms and are made up of sub – atomic  
particles called protons, neutrons and electrons  
Atoms join together to form molecules  
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The figures below show the atoms in solid , liquid and gas respectively  
Kinetic theory of matter (molecular theory of matter)  
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The kinetic theory of matter describes the physical properties of matter in terms  
of the behavior of its component atoms or molecules  
It states that: “All matter is made up of very small particles that are in  
constant motion”  
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T
he more heat energy the particles possess the faster they move  
In a solid, the particles are arranged close together in a regular pattern and  
vibrate in fixed positions hence possess lowest kinetic energy  
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In a liquid, the particles are still close together but in an irregular arrangement.  
Particles in a liquid move about and are able to slide past one another  
In gas, the particles are far apart, moving rapidly and bouncing off the wall of  
the container  
The table below summarize the properties of these states of matter  
Properties of three states of matter  
Solid  
Liquid  
Gas  
Particles are closely  
packed together  
Has definite shape and  
volume  
Particles are slightly  
further apart  
Takes the shape of the  
container holding it .has  
definite volume  
Particles are further apart  
Has neither definite shape  
nor volume  
Has strongest inter-  
molecular forces  
Inter-molecular forces are  
moderately strong  
Has weak inter –  
molecular forces  
Particles are not free to  
move. They just vibrate in  
a fixed positions instead  
Particles move with a  
moderate speed  
Particles move randomly  
with a high speed  
Has low kinetic energy  
Moderate kinetic energy,  
enough to ’stretch’ the  
intermolecular forces  
High kinetic energy  
enough to break all inter –  
molecular forces  
The concept of Brownian movement  
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Brownian movement is the irregular motion of tiny particles suspended in a  
fluid (fluid or gas)  
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Robert Brownian, an English Botanist discovered that, the random motion of  
the pollen grains in water was caused by the collisions between them and the  
molecules of water  
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This motion is called Brownian movement (motion)  
Molecular properties of matter include the following;  
1. Elasticity  
2. Adhesion and cohesion  
3. Surface tension  
4. Capillarity  
5. Osmosis  
6. Diffusion  
Elasticity  
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Is the ability of a body to return to its original shape and size after deformation.  
OR  
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Is the ability of a body to resist any permanent change to it when stress is applied  
A body with the ability to undergo elasticity is called Elastic material.Eg spring  
Materials are elastic to some degree until elastic limit is reached  
A material which does not undergo elastic deformation is called Brittle material.  
For example, glass, block etc  
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When material deformed beyond the elastic limit it becomes plastic, means it  
will not regain its original shape even though it does not break. This type of  
deformation is called PLASTIC DEFORMATION  
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A Material which does not return to its original shape and size after deformation  
is called INELASTIC or PLASTIC material. E.g plastic bags, plastic utensils etc  
Relationship between tension and extension of a loaded elastic material  
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This can be explained in Hooke’s law which states that:  
“Within the elastic limit, the extension is directly proportional to the  
force applied”  
OR  
“Provided that the elastic limit of a body is not exceeded, the extension  
is directly proportional to the force applied”  
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ension can be described as the force (F) transmitted within a string or rope or  
wire when it is stretched or elongated  
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Extension (e) is an excess length obtained after stretching a wire (rope or string)  
Hooke’s law describes that when a force is applied to a material, the length of  
the material will keeps increasing in the same proportion as the force  
If the limit of extension (elastic limit) is not reached, the material can return to  
its original shape and size after removing the applied force  
But when the elastic limit is reached then the body will not return to its original  
shape and size even after the removal of the force applied  
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Mathematically Hooke’s law can be expressed as:  
풂풑풑풍풊풆풅 풇풐풓풄풆 ∝ 풆풙풕풆풏풔풊풐풏  
푭 ∝ 풆  
→ 푭 = 풌 풆 푾풐풓풌 풅풐풏풆 = 푨풓풆풂 풐풇 풕풉풆 품풓풂풑풉 = ퟏ  
푭풆  
ퟐ
푭
풌 =  
(Whereby k = Force constant or spring constant)  
풆
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The SI unit of k is Newton per metre (N/m)  
The area under the graph of proportionality of Load against extension gives the  
work done in stretching a spring, see the figure below  
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Therefore And the work done in stretching the spring is given by  
ퟏ
Work done = 푭풆 = ퟏ 풌풆ퟐ  
ퟐ
ퟐ
T
he relationship between tension and extension of a loaded elastic material  
can also be explained using the following graph  
The graph of Tension against extension  
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Interpretation of the graph  
Between point O and A (O – A)  
The tension is direct proportional to extension. This was discovered by Hooke and  
finally he came with a law which called Hooke’s law.  
At this stage, the body can regain its original shape and size if tension is removed  
At point A  
Point A is called the limit of proportionality or elastic limit  
Between point A and B (A – B)  
This is called the region of elastic. In this region a small force produces a large  
extension which is not directly proportional to the extension  
Between point B and C (B – C)  
This is known as the region of plastic deformation. At this region material will not  
return to its original shape and size when applied force (tension/load) is removed  
Beyond point C  
Beyond this point the body becomes thinner and ultimately break due to excessive  
application of force  
Application of elasticity  
At homes is applied in  
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Rubber gaskets that seal the refrigerator door  
Clothing  
Springs in furniture  
Rubber bands that holds things together  
Toys like balloons and balls  
In transportation, elasticity may be applied in:  
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Rubber tyres, hoses, belt and shock absorbing springs for car and trucks  
Aeroplane wings  
Supporting cables for bridges  
In Industry, elasticity is applied in:  
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Conveyor belts  
Measuring weight  
Steel beams used in constructions  
Insulation of vibration and sound  
Surface Tension  
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Is the ability of a liquid surface to behave like a fully stretched elastic skin.  
OR  
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Is a force present within the surface layer of a liquid that causes the layer to  
behave as an elastic sheet.  
Causes of surface tension  
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Surface tension is the result of inter – molecular cohesive bonding among the  
molecules of a liquid.  
(Surface tension occurs due to the force of attraction between molecules of a liquid)  
Application of surface tension (Examples of surface tension)  
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Walking of pond skater on the surface of water  
Floating of a needle on the surface of water  
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Mosquito eggs can float on water because of its surface tension  
Soaps and detergents lowering the surface tension during washing of clothes  
Surface tension prevents water from passing through the pores of an umbrella  
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Warm water is used for washing purpose as heating increases the surface  
area and reduces surface tension  
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Antiseptics like Dettol have low surface tension, so that they spread faster  
Toothpaste contains soap ,which reduces the surface tension and helps it  
spread freely in the mouth  
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Hot soup has a lower surface tension than cold soup, hence hot soup is  
tastier than cold soup.  
Factors affecting Surface Tension  
Nature of the liquid  
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Different liquids have different surface tension, For example, mercury has  
higher surface tension than water  
Contamination (impurities)  
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Impurities in a liquid lower the surface tension. The substance which lowers  
surface tension is called SURFACTANTS (acronym for surface active agent).  
Example of surfactants is detergents  
Temperature  
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Surface tension of a liquid decreases with increase in temperature  
Intermolecular Force  
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Is the force of attraction or repulsion between particles of matter (atoms/ molecules)  
Types of Intermolecular Forces  
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Cohesive force  
Adhesive force  
Cohesion  
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s the force of attraction between the molecules of the same substance.  
For example, water and water molecules  
Definite shapes of a solid are due to strong cohesion force among its molecules  
Adhesion  
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Is the force of attraction between the molecules of different substances.  
For example water to glass molecules  
Effect of Adhesion and Cohesion  
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Mercury forms convex (downward) meniscus because it possess strong  
cohesive force than adhesive force  
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Water forms concave (upward) meniscus because it possess strong adhesive  
force than cohesive force  
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Drop of water on the surface of some leaves is perfect sphere due to strong  
cohesive force than adhesive force  
Drop of mercury on the surface of different material is perfect sphere due to  
strong cohesive force than adhesive force  
Water spread over a glass because it possess strong adhesive force than  
cohesive force  
Application of Adhesive and Cohesive force  
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Adhesion is used to stick two different objects together .E.g using glue or tape  
Adhesion is used to remove harmful materials from drinking water e.g bacteria  
The bodies of Plants and animals use the cohesion of tissue to repair damage  
Ink sticks on paper because of adhesive force between the paper and ink  
Cohesion assists in transport of water in plants and animals by allowing one  
molecule to pull others along with it (While Adhesion occurs when the water  
molecules cling to the xylem tissue)  
Capillarity (Capillary action)  
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Is the ability of liquid to rise or fall in a narrow tube.  
OR  
OR  
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s the tendency of a liquid to rise in a narrow tube or to be drawn into small openings  
s the ability of a liquid to flow against gravity in a narrow space (thin tube)  
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When you dip a capillary tube in water, the water rises due to greater adhesive force  
When you dip a capillary tube in mercury, the mercury falls due to greater cohesive force  
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The greater adhesive and cohesive force, the greater the capillary action  
Application of Capillarity  
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The raising of oil in the wicks of lamps in the cotton threads  
The absorption of water by a towel (paper or cloth)  
Water rises in the soil because the soil is composed of fine particles  
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It facilitates the transport of water and nutrients from the roots  
Ink rises into the blotting paper through those fine pores  
It Promotes the movement of ground water  
Cotton clothing in hot climates uses capillarity action to draw perspiration away  
from the body  
Osmosis  
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Is the movement of a solvent from a region of low concentration to a region of  
high concentration through a semi-permeable membrane.  
Consider the experiment below  
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Peal a potato  
Keep over salts  
The potato shrink due to movement of water from potato (low concentration) to  
salt (high concentration)  
Application of Osmosis  
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Removal of harmful ingredients from drinking water  
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Controls the movement of water and nutrients in and out of the cell  
Removing salt from seawater so as to make it suitable for drinking and other domestic uses  
Absorption of water molecules from soil to plant  
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Aquatic life is controlled by osmosis  
Filtration processes  
Diffusion  
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Is the movement of particles from a region of high concentration to one of low  
concentration.  
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For example, spraying of a perfume  
Application of Diffusion  
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Detecting harmful substance in the environment  
In the use of refreshers and other sprays  
Respiration process, oxygen diffuses into blood stream  
Balance concentration of water and nutrients in and out of the cells of living  
organisms.