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Introduction |
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A spider web is stronger than steel of the same thickness. Its elastic limit is greater than that of steel. |
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Intermolecular Forces and Interatomic Forces |
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When two wet glass plates are pressed together, they cannot be separated easily. This is because of the force of attraction existing between the atoms and molecules, and are electrical in origin. |
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Crystalline and Amorphous Solids |
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Solids have definite shape and volume because the average distance between the molecules or atoms remain constant and do not change with time. The arrangement of molecules inside a solid differ from one to another. |
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Elasticity and Deforming Forces |
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External forces acting on a body, bring about a change in its state or configuration. The latter is possible when the body is not free to move, but the molecules are compelled to change their positions. Such forces are called deforming forces. |
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Stress |
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Elastic bodies regain their original shape due to internal restoring forces. This internal restoring force, acting per unit area of a deformed body, is called a stress. |
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Strain |
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The change in configuration of a body depends on the type of stress. The ratio of change in configuration to the original configuration is called a strain. Strain, being a ratio, does not have any units or dimensions. |
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Hooke's law |
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Experimental study by Hooke revealed that elastic bodies regain their original configuration completely, only upto a limit. He termed this limit as the elastic limit. He found that within the elastic limit, the extension produced in the wire was directly proportional to the load applied. |
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Types of Modulus of Elasticity |
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Corresponding to the three types of strains, there are three types of modulus. Young's Modulus of elasticity. |
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Applications of Elasticity |
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Mechanical properties like strength, stiffness (Rigidity), ductility, malleability and brittleness have to be carefully studied to select a material for a particular job. |
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Introduction |
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Fluids are substances which begin to flow when external force is applied on them. Liquids and gases are fluids. Fluids do not have a definite shape. The branch of physics, dealing with the study of fluids at rest is called hydrostatics. |
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Pressure |
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Pins and nails have pointed ends so that, when a pin is pressed, high pressure is applied on the surface with lesser force, as area is small. |
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Pascal's law |
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Blaise Pascal, a French physicist, discovered that the pressure in a fluid in equilibrium is the same everywhere, if the effect of gravity is neglected. |
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Applications of Pascal's law |
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A hydraulic lift is used to lift heavy loads. It consists of two pistons of varying cross-sectional area. The two pistons are connected to each other with a horizontal pipe. |
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Archimede's Principle |
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An iron needle sinks in water but a huge ship floats on the surface of water. |
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Floating and Sinking |
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Let W = Vrg be the true weight of body, acting through the centre of gravity and let 'w' be the weight of the liquid displaced, acting through the centre of gravity of the displaced liquid (called the centre of buoyancy). |
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Applications of Archimedes' Principle |
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A floating ship displaces water equal to its own weight, including that of cargo. |
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Introduction |
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When two solid surfaces slide over each other, a frictional force acts between them that opposes the relative motion of the bodies. Similarly, when a layer of a liquid slips on another layer the two exert a tangential force on another. This opposes their motion. The property of a liquid by virtue of which, a tangential force acts so as to oppose relative motion between its layers, is called viscosity. |
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Types of Liquid Flow |
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In the streamline flow of a liquid, every particle of the liquid follows the same path as the preceding particle. So, it has the same velocity (in magnitude and direction) as the preceding particle. The path of the particle is either straight or curved. Crowding of the paths or streamlines, indicates greater velocity of the liquid particles. |
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Critical Velocity |
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Critical velocity is the velocity of a liquid flow upto which its flow is streamlined and after which its flow becomes turbulent. |
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Stoke's Law |
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When small spherical bodies move through a viscous medium, the bodies drag the layers of the medium that are in contact with them. This dragging results in relative motion between different layers, which are away from the body. Therefore, a viscous drag comes into play, opposing the motion of the body. It is found that this backward force or viscous drag, increases with increase in velocity of the body. |
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Equations of Continuity |
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Consider a non-viscous liquid in streamline flow through a tube AB, of varying cross-section. Let A1 and A2 be the area of cross-section at A and B respectively. |
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Bernoulli's Theorem |
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This theorem is a consequence of the principle of conservation of energy, applied to ideal liquids in motion. |
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Application of Bernoulli's Theorem |
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When we blow air over a strip of paper as shown in the above figure, we find that the paper moves up. This is because, on blowing air, the velocity of air increases, creating low pressure above the paper and high pressure below the paper. |
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Introduction |
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When a thermometer is dropped accidentally, we find the mercury inside the bulb of the thermometer rolling down as small perfect spheres. Raindrops and soap bubbles are also perfectly spherical in shape. A plastic strainer floats on water which is unusual. |
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Definition of Surface Tension |
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It is a property by virtue of which, the free surface of a liquid possesses a tendency to contract so as to acquire a minimum surface area. |
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Origin of Surface Tension (Molecular Theory) |
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Liquids, according to the Molecular theory, are made up of molecules. Let KLMN represent a surface film of thickness LM, which is same as the molecular range. Consider three molecules A, B, C at different positions. |
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Surface Energy |
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We know that work has to be done in order to bring a molecule, from interior to the surface, against the force of cohesion. If the surface area is increased, more molecules can be accommodated at the surface. Increase in surface area, results in cooling. To maintain the temperature, heat flows from the surroundings to the film and this is added on. This additional energy is termed as 'surface energy'. |
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Applications of Surface Tension |
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Surface tension of soap solution is less, it can spread over large areas and wash clothes more effectively, since the dirt particles stick to the soap molecules. |
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Factors affecting Surface Tension |
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The presence of impurities either on the surface or dissolved in it, affect surface tension of the liquid. Highly soluble substances increase the surface tension of water, whereas sparingly soluble substances reduce the surface tension of water. |
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Capillarity |
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When one end of a glass capillary tube that is open at both ends, is dipped in a liquid like water that wets the tube, the liquid level in the tube rises to a certain height above the liquid level in the container, as shown below. |
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Angle of Contact and Shape of Meniscus |
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The above figure shows two liquids, one liquid which wets the glass and the other (i.e. diagram 'b') which does not wet the glass. In the first case, the force of adhesion (i.e. force of attraction between unlike molecules) is more than the force of cohesion (i.e. force of attraction between like molecules). |
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Shape of Meniscus |
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The free surface of a liquid called meniscus, assumes a flat, convex or concave shape, depending on the solid and liquid surface. |
