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Which of the following is NOT true about Frictional force? A. Friction is the force which opposes the relative motion of two surfaces in contact. B. The force of friction that acts when a body is moving (sliding) on a surface is called sliding friction. C. Friction in machines wastes energy and also causes wear and tear. D. Rolling friction is much more than sliding friction, the use of ball bearings in a machine considerably reduces friction.
Consider the following statements in connection with thrust bearings: 1) Cylindrical thrust bearings have higher coefficient of friction than ball thrust bearings. 2) Taper rollers cannot be employed for thrust bearings. 3) Double-row thrust ball bearing is not possible 4) Lower race, outer race and retainer are readily separable in thrust bearings. Which of the above statements are correct?
Sliding contact bearings, also called plain bearings have no problem of wear.
Two involute gears in a mesh have path of approach = 29.83 mm and path of recess = 21.09 mm. The larger gear has 40 teeth and the pinion has 12 teeth. Find the ratio of the sliding to rolling velocity at the: i) beginning of contact ii) end of contact iii) pitch point r = 72 mm
Which of the following is correct about friction? I. Rolling friction is smaller than the sliding friction II. Sliding friction is smaller than static friction 
Which of the following is correct? I. Sliding friction is smaller than static friction. II. Rolling friction is smaller than sliding friction.
Consider the following statements: In case of helical gears, teeth are cut at an angle to the axis of rotation of the gears. 1) Helix angle introduces another ratio called axial contact ratio. 2) Transverse contact ratio is equal to axial contact ratio in helical gears. 3) Large transverse contact ratio does not allow multiple teeth to share the load. 4) Large axial contact ratio will cause larger axial force component Which of the above statements are correct?
Consider the following statements: 1. The kinetic friction is always less than the rolling friction. 2. The kinetic friction is always equal to the rolling friction. 3. The kinetic friction is always greater than the rolling friction. Which of the following statement is correct?
The sliding contact bearings are lower kinematic pairs.
Ball bearings are preferred over other types of bearings for machines rated up to 75 kW. Which of the following is not true for ball bearings?