Class 8 Science Chapter 9 MCQ

Force of friction acts in solids, liquids and gases and opposes the motion with respect to each other.

Stone will be more suitable because it will exert greater reaction and hence greater friction force which sharpen the blade of a knife easily by rubbing.

As we know that friction force acts in an opposite direction to the direction in which an object moves. If a big wooden box is being pushed on the ground from east to west direction. The force of friction due to ground will act on “east direction”.

The spring balance is a device which is used for measuring force acting on an object. The spring balance contain a coiled spring which gets stretched when a force is applied to its free end or hook end. When the spring balance is held vertically, it is said to measure the weight of an object hung from its hook, because weight of an object is also a force. Therefore, a spring balance is a device, used to measure force acting on an object and weight of an object.

The friction will decrease because oil acts as a lubricant which reduce friction.

The friction between two surfaces depends on two factors first is, the nature of the two surfaces or smoothness or roughness of the two surfaces and second is, the force with which two surfaces are pressed together or weight. But amount of surface area of the two objects which is in contact with each other does not depend on the friction force.

Talcum powder reduces friction force and the ball will cover longer distance.

There are many advantages and disadvantages of friction force. Here, all are the advantages mentioned in all options, except one i.e., option [C]. Friction enables rubber pads to be rubbed off, the tyres of vehicles wear out gradually, soles of our shoes tear out, brake pads of vehicles rubbed off also.

We know that friction force acts in an opposite direction to the direction in which an object moves. The maximum frictional force present between two objects is static friction. And sliding friction is smaller than static friction. And rolling friction is much less than sliding friction. Here, sliding friction is less than rolling friction is incorrect. Rest of all are correct.

We know that friction force acts in an opposite direction to the direction in which an object moves. The maximum frictional force present between two objects is static friction. And sliding friction is smaller than static friction. And rolling friction is much less than sliding friction. The relationship between the three types of friction is: The static friction > Sliding Friction > Rolling friction. Thus, the rolling friction will be less than 20N.

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

The friction between two surfaces depends on two factors first is, the nature of the two surfaces or smoothness or roughness of the two surfaces and second is, the force with which two surfaces are pressed together or weight. As the roughness of the surface increases, the friction increases. Here, glazed paper, glass table top and aluminium frame produces less friction than “sand paper”. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Friction is a phenomenon which resists motion when an object is rubbed against another. So, friction has instances where it is desired and instances where it is not desired. In the case of automobiles, friction is desired when we wish to stop the moving car and friction is less desired when it creates a drag on the movement of the vehicle. Given the case, all four cases have same mass and speed. So, the effectiveness of the brake is with the smallest distance traveled after the brake where friction is the maximum. Therefore, where friction force is maximum objects covers less distance. Here, 4.8 m is least distance. Hence your answer will be option [C].

Friction is caused by the interlocking of irregularities in the surfaces of the two objects which are in contact with each other. Sliding friction is between two objects when one or both are sliding against each other. In this case, the book is sliding down the titled table. So, the motion is directed downwards. So, the friction will act on the book in the direction opposite to movement. So, friction will act upwards. Sliding friction is less than static friction, so when the table is titled, the book starts to slide. Here, your answer will be option [B].

Here, all the statements are correct. Hence, your answer will be option [D].

Using a dry lubricant or talcum powder to reduce the friction on carom board.

Remember, friction enables a ladder to be leaned against the wall and not slip down to the floor. The irregularities capture the both ends of ladders.

The fluid friction can be reduced or minimized by giving special shape called “streamlined shape”. They have a special shape. Aeroplane, rockets, birds, fish, car have streamlined shape. But, bus has no streamlined shape.

Here, all the statements are correct. Hence, your answer will be option [D].

Mustard oil reduces the friction on his hands. So, Glass tumbler will be most difficult to handle. Rest of all have much irregularities to hold. And glass has very smooth surface. Hence, your answer will be option [C].

Friction is force that only occurs when an object moves. The force of friction acts in the direction opposite to the direction of motion of an object.

Wrapping of jute clothes make the surface of brick more-rough due to which the friction with floor increases.

When the wheel revolves, the balls of ball bearing roll and reduce friction. So, the use of ball bearing makes the wheel roll smoothly over the axle. Since rolling friction is much smaller than the sliding friction, sliding friction is replaced in most of the machines by rolling friction by using ball bearings. Therefore, ball bearing is a device which usually converts sliding friction into rolling friction.