Mechanics lab reports, Schemes and Mind Maps of Mechanics

Download Mechanics lab reports and more Schemes and Mind Maps Mechanics in PDF only on Docsity! TO FIND COEFFICIENT OF FRICTION BETWEEN PULLY AND BELT FRICTION force that resists the sliding or rolling of one solid object over another. Frictional  forces, such as the traction needed to walk without slipping, may be beneficial, but  they also present a great measure of opposition to motion. About 20 percent of the  engine power of automobiles is consumed in overcoming frictional forces in the  moving parts. STATIC FRICTION DYNAMIC FRICTION LIMITING FRICTION Static friction is friction between  two or more solid objects that are not moving relative to each other. For example, static friction can  prevent an object from sliding  down a sloped surface. The  coefficient of static friction,  typically denoted as μs, is usually  higher than the coefficient of  kinetic friction. Static friction is  considered to arise as the result  of surface roughness features  across multiple length scales at  solid surfaces.  Kinetic friction,   also   known as dynamic friction or sliding friction,  occurs  when   two objects are moving relative to each other and rub together (like a sled on the ground).  The coefficient  of  kinetic friction   is   typically   denoted   as μk, and   is   usually   less   than   the coefficient of static friction for the same materials.   The friction force between two surfaces after sliding begins   is   the   product   of   the coefficient   of   kinetic   friction   and the normal force. Limiting friction occurs when the moving force and the force opposing motion are equal; any addition to the moving force will cause slipping. The limiting frictional force is proportional to the normal reaction between the contacting surfaces and is independent of the area of contact. FLAT AND V BELT V belt Flat belt V belts (also style V-belts, vee belts, or, less  commonly, wedge rope) solved the slippage and  alignment problem. It is now the basic belt for  power transmission. They provide the best  combination of traction, speed of movement, load  of the bearings, and long service life. They are  generally endless, and their general cross-section  shape is roughly trapezoidal. The "V" shape of the  belt tracks in a mating groove in the pulley, with the result that the belt cannot slip off. The belt also  tends to wedge into the groove as the load  increases—the greater the load, the greater the  wedging action—improving torque transmission  and making the V-belt an effective solution, needing less width and tension than flat belts. Flat belts were traditionally made of leather or fabric. Today most are made of rubber or synthetic polymers. Grip of leather belts is often better if they are assembled with the hair side (outer side) of the leather against the pulley, although some belts are instead given a half- twist before joining the ends (forming a Möbius strip), so that wear can be evenly distributed on both sides of the belt. Flat belts also tend to slip on the pulley face when heavy loads are applied, and many proprietary belt dressings were available that could be applied to the belts to increase friction, and so power transmission. GROOVE In manufacturing or mechanical engineering a groove is a long and narrow indentation built into a material, generally for the purpose of allowing another material or part to move within the groove and be guided by it. Examples include: A canal cut in a hard material, usually metal. This canal can be round, oval or an arc in order to receive another component such as a boss, a tongue or a gasket. It can also be on the circumference of a dowel, a bolt, an axle or on the outside or inside of a tube or pipe etc. This canal may receive a circlip an o-ring or a gasket. A depression on the entire circumference of a cast or machined wheel, a pulley or sheave. This depression may receive a cable, a rope or a belt. A longitudinal channel formed in a hot rolled rail profile such as a grooved rail. This groove is for the flange on a train wheel. COEFFICIENT OF FRICTION Coefficient of friction is a measure of the amount of friction existing between two surfaces.  When you find a coefficient of friction, you’re calculating the resistance to motion at the  interface of two surfaces of similar or dissimilar materials.  The power of this friction force depends on the materials that are pressing against one another. For instance, a steel bar will slide much more easily on a sheet of ice than on a slab of concrete.  In these examples, the steel-on-ice combination has a much lower coefficient of friction. Apparatus :  Belt and Pully Apparatus  Spring Balance  Flat Belt  V Belt  Hanger  Weights 4. Procedure : Flat Belt  Put the Flat Belt on the apparatus and make the angle of the pully equal to 30◦.  Put a weight on the hanger and calculate the tension corresponding to that weight.  Repeat the experiment for another weight.  Repeat the experiment for third weight such that you three values of tension at three different values for weights for a same value of angle.  Repeat the procedure for other angles up to 150 with the step size of 30◦.  Weight is also acting as a tension T1 and corresponding tension is T2.  Now calculate the coefficient of friction at each value of angle using this formula: