**Friction**

- This video introduces us to the concept of friction as the opposing force acting between two surfaces in contact. It also explains the difference between static and kinetic friction with help of graph.
- This video explains the reason behind the force of friction at microscopic level in detail and its dependence upon normal reaction.
- This video explains the coefficients of static and kinetic friction with their equation and range of values.
- A block lies on a floor at rest. What is the magnitude of the frictional force on it from the floor? If a horizontal force of 5 N is now applied to the block, but the block still does not move, what is the magnitude of the frictional force on it? If the maximum value of the static frictional force on the block is 10 N, will the block move if the magnitude of the horizontally applied force is 8 N? what If it is 12 N?
- A block of mass m is placed on a rough surface and the angle of the surface with respect to horizontal is increased slowly. At a given angle, the block just starts to slip. Find the coefficient of static friction between the block and the surface.
- Coefficient of friction can be greater than unity. Statement 2: Force of friction is dependent on normal reaction and ratio of force of friction and normal reaction cannot exceed unity. Tell which of the above given statement is correct and whether statement 2 is correct explanation of statement 1.
- State whether the following statement is true or false. Static friction is always greater than the Kinetic friction.
- Mark the correct statement(s) regarding friction. (a) Friction can be zero, even though the contact surface is rough (b) Even though there is no relative motion between surfaces, frictional force may exist between them (c) The expressions FS = µs N or FK = µk F are approximate expressions (d) The expression FS = µs N tell that direction of FS and N are the same
- The contact force exerted by a body A on another body B is equal to the normal force between the bodies. Which of the following statement is true? (a) the surface must be frictionless (b) the force of friction between the bodies is zero (c) the magnitude of normal force equals that of friction (d) the bodies may be rough but they don't slip on each other.
- A boy of mass M is applying a horizontal force to slide a box of mass M' on a rough horizontal surface. The coefficient of friction between the shoes of the boy and the floor is m and between the box and the floor is m'. In which of the following cases it is certainly not possible to slide the box? (a) m < m', M < M' (b) m > m', M < M' (c) m < m', M > M' (d) m > m', M > M'
- This video describes the key feature of friction like its direction, area of impact, its dependence upon the area of contact and angle of friction
- This video gives a detailed description of methods of finding the direction of friction for static and kinetic conditions. The direction of friction is always such that it opposes the relative motion between two surfaces.
- Find the direction of friction on a block sliding down a rough incline plane at an angle with constant velocity.
- Find the direction of friction on a block sliding down a rough incline plane at an angle with constant velocity.
- Find the direction of friction between the two blocks kept over each other, as shown in figure; if both are moving with same constant velocity towards right.
- Identify the role of force of friction in the process of walking.
- A horizontal force F pushes a block of known weight against a vertical wall. The coefficient of static and kinetic between the wall and the block are given. Assuming that the block is at rest initially, answer the following (a) Will the block move? (b) What is the force on the block from the wall?
- A block m1 kept on a rough, horizontal surface is connected to m2 by a string over an ideal pulley as shown in figure. Determine the magnitude of the acceleration of the two objects. Given the coefficient of kinetic friction between the block and the surface is known.
- A block m1 kept on a rough, horizontal surface is connected to m2 by a string over an ideal pulley as shown in figure. Determine the magnitude of the acceleration of the two objects. Given the coefficient of kinetic friction between the block and the surface is known.
- The two blocks shown in figure are not attached to each other. The coefficient of static friction between the blocks is known and surface beneath the larger block is frictionless. Find the minimum magnitude of the horizontal force F required to keep the smaller block from slipping down the larger block.
- As shown in figure, the three blocks with given mass attain a given acceleration, when released from rest. Find the coefficient of kinetic friction between block 2 and the table.
- In the figure, mass of body A and B, the coefficients of friction between A and the incline, and the angle of inclination are given. Let the positive direction of x-axis be up the incline. In unit-vector notation, what is the acceleration of A, if A is initially (a) at rest, (b) moving up the incline, and (c) Moving down the incline?
- A block of mass m1 is kept on a fixed inclined plane and attached to a block of mass m2 by a rope over a pulley as shown in Figure. The angle of inclination with horizontal and the coefficient of friction are given. Find range of m2 for which m1 remains at rest.
- As shown in figure, two boxes m1 and m2 slide down an inclined plane while attached by a mass-less rod parallel to the plane. The coefficient of kinetic friction between surfaces is given. Find a) The tension in the rod (b) The magnitude of the common acceleration of the two boxes. (c) How would the answer to above questions change if the boxes shift their position with each other?
- A slab of mass m1 rests on a frictionless floor, and a block of mass m2 rests on top of the slab. Between block and slab, the coefficients of static friction and kinetic friction are known. If the block is pulled by horizontal force F, what will be the resulting accelerations of the block and the slab?
- Consider the situation shown in figure. The friction coefficient between the two blocks is known and the floor is smooth. What maximum horizontal force F can be applied without disturbing the equilibrium?
- The friction coefficient between the board and the floor as shown in figure is given. Find the maximum force that the man can exert on the rope so that the board does not slip on the floor.
- As shown in the figure, two blocks A and B with known masses are placed on a surface. The coefficient of friction between all the surfaces is known. A Force F is applied on block A (a) Find acceleration of blocks if the ground is considered to be frictionless, (b) find acceleration of blocks for different value of force F.
- In figure, for a given mass of A and C, a) Determine the minimum weight of block C to keep A from sliding if coefficient of friction between ‘A’ and the table is 0.20. b) Block C suddenly is lifted off A. What is the acceleration of block A if coefficient of kinetic friction between ‘A’ and the table is 0.15? c) If weight of C is equal to half of that calculated in part (a) Also find the acceleration of block A and C when the system is released for given value of coefficient of friction between A and C.
- The coefficient of friction between the two blocks and that between the bigger block and the ground are known. Find the acceleration of the block of mass m2 in the situation as shown in figure.
- A crate slides down a right-angled trough inclined at an angle .The coefficient of kinetic friction between the crate and the trough is given. The acceleration of the crate will be …..?
- Consider the situation shown in figure. The horizontal surface below the bigger block is smooth. The coefficient of friction between the blocks is given. Find the minimum and the maximum force F on block ‘C’ that can be applied in order to keep the smaller blocks at rest with respect to the bigger block.
- A boat is traveling at some speed v when its engine is shut off. The magnitude of the frictional force fk between boat and water is proportional to the speed v of the boat as fk = 70 v. Find the time required for the boat to slow down to half of its initial speed.
- A small body A starts sliding down from the top of wedge whose base legth is given. The coefficient of friction between the body and the wedge surface is known. At what value of the angle of inclination, will the time of sliding be the least?
- A small body A starts sliding down from the top of wedge whose base legth is given. The coefficient of friction between the body and the wedge surface is known. At what value of the angle of inclination, will the time of sliding be the least?
- A block of mass m1 is placed on a block of mass m2, which rests on a smooth horizontal plane as shown in figure. The coefficient of friction between the blocks is known. The block m2 is subjected to the horizontal force F depending on time t as F = Kt (K is a constant). Find (a) the moment of time t at which the blocks start sliding and (b) the acceleration a1 and a2 of the two blocks respectively.
- A block of mass m1 is placed on a block of mass m2, which rests on a smooth horizontal plane as shown in figure. The coefficient of friction between the blocks is known. The block m2 is subjected to the horizontal force F depending on time t as F = Kt (K is a constant). Find (a) the moment of time t at which the blocks start sliding and (b) the acceleration a1 and a2 of the two blocks respectively.