Railways NTPC (Technical Ability) Theory of Machines and Machine Design Theory of Machines

Theory of Machines

• The subject Theory of Machines may be defined as that branch of Engineering - Science, which deals with the study of relative motion between the various parts of machine, and forces which act on them. The knowledge of this subject is very essential for an engineer in designing the various parts of a machine.
• Kinematics -It is that branch of Theory of Machines which deals with the relative motion between the various parts of the machines with out forces applying to it.
• Dynamics- It is that branch of Theory of Machines which deals with the forces and their effects, while acting upon the machine parts in motion.
• Kinetics- It is that branch of Theory of Machines which deals with the inertia forces which arise from the combined effect of the mass and motion of the machine parts.
• Statics- It is that branch of Theory of Machines which deals with the forces and their effects while the machine parts are at rest. The mass of the parts is assumed to be negligible.
• Kinematics is the branch of mechanics concerned with the motions of objects without being concerned with the forces that cause the motion. In this latter respect it differs from dynamics, which is concerned with the forces that affect motion.
• There are three basic concepts in kinematics - speed, velocity and acceleration.
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• In mechanics and physics, simple harmonic motion is a type of periodic motion where the restoring force is directly proportional to the displacement. It can serve as a mathematical model of a variety of motions, such as the oscillation of a spring.
• In addition, other phenomena can be approximated by simple harmonic motion, including the motion of a simple pendulum as well as molecular vibration.
• Simple harmonic motion is typified by the motion of a mass on a spring when it is subject to the linear elastic restoring force given by Hooke's Law. The motion is sinusoidal in time and demonstrates a single resonant frequency.
• In order for simple harmonic motion to take place, the net force of the object at the end of the pendulum must be proportional to the displacement.
• Simple harmonic motion provides a basis for the characterization of more complicated motions through the techniques of Fourier analysis.
• Velocity and acceleration analysis of mechanisms can be performed vectorially using the relative velocity and acceleration concept. Usually we start with the given values and work through the mechanism by way of series of points A, B, C, etc.
• Friction is resistance to motion, which also resist the other body from its motion in particular direction.
• It is the co which may be parralel or non-parralel depending on type of drive usedmponents which is used for the motion transfer or power transmission from one s. Belts are flexible made of rubber, fibers etc.
• Chains are made of metals which are positive drive meands that no slip occurs. Rope are used where centre distance-distance-distance is very large. Ropes are made of fibers and metal wires depending on load conditions.
• If the centre of gravity of a body of mass M has linear acceleration a, then the resultant of the external forces acting on the body must be Ma.
• Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass.
• Centre of gravity is the point in or near a body at which the gravitational potential energy of the body is equal to that of a single particle of the same mass located that point, and through which the resultant of the gravitational forces on the component particles of the body acts
• Of gravity is the point in or near a body at which the gravitational potential energy of the body is equal to that of a single particle of the same mass located at that point, and through which the resultant of the gravitational forces on the component particles of the body act.
• A force is any influence that causes a free body to undergo a change in speed, a change in direction, or a change in shape. Force can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity, i.e., to accelerate, or which can cause a flexible object to deform.
• This latter force is called the Inertia Force and it is numerically equal to the product of mass and acceleration of the centre of gravity. It acts in the opposite direction to the acceleration.
• The system of external forces and inertia forces is treated as if in statical equilibrium. Note that the use of centrifugal force in governor problems is a particular example of this principle.
• Using boiling water to produce mechanical motion goes back about 2,000 years, but early devices were not practical. Since the late 1700s steam engines have become a major source of mechanical power.
• The first applications were removing water from mines. In 1781 James Watt patented a steam engine that produced continuous rotative motion.
• These 10 hp engines enabled a wide range of manufacturing machinery to be powered. The engines could be sited anywhere that water and coal or wood fuel could be obtained. Within a century.in 1883, engines that could provide 10,000 hp were feasible.
• Steam engines could also be applied to vehicles such as traction engines and the railway locomotives which are commonly just called steam engines outside America.
• The stationary steam engine was an important component of the Industrial Revolution, overcoming the limitations imposed by shortage of sites suitable for water mill and allowing factories to locate where water power was unavailable.
• Governor is a devise used for control the quantity of fuel according to the speed so control the variation of speed due to varying load. These are generally applied on IC engines but it also applied some time on steam turbines and gas turbines.
• A dynamometer or "dyno" for short, is a device for measuring force, moment of force (torque), or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed (RPM).
• A dynamometer can also be used to determine the torque and power required to operate a driven machine such as a pump. In that case, a motoring or driving dynamometer is used.
• A dynamometer that is designed to be driven is called an absorption or passive dynamometer. A dynamometer that can either drive or absorb is called a universal or active dynamometer.
• In addition to being used to determine the torque or power characteristics of a machine under test (MUT), dynamometers are employed in a number of other roles.
• In standard emissions testing cycles such as those defined by the United States Environmental Protection Agency (US EPA), dynamometers are used to provide simulated road loading of either the engine (using an engine dynamometer) or full powertrain (using a chassis dynamometer).
• In fact, beyond simple power and torque measurements, dynamometers can be used as part of a test bed for a variety of engine development activities, such as the calibration of engine management controllers, detailed investigations into combustion behavior, and tribology.
• In the medical terminology, hand-held dynamometers are used for routine screening of grip and hand strength, and the initial and ongoing evaluation of patients with hand trauma or dysfunction. They are also used to measure grip strength in patients w here compromise of the cervical nerve roots or peripheral nerves is suspected.
• In the rehabilitation, kinesiology, and ergonomics realms, force dynamometers are used for measuring the back, grip, arm, and/or leg strength of athletes, patients, and workers to evaluate physical status, performance, and task demands.
• Typically the force applied to a lever or through a cable is measured and then converted to a moment of force by multiplying by the perpendicular distance from the force to the axis of the level.