Question

Which of the following describe a frictional force? This question has multiple correct options
A.) Frictional force always opposes the state of motion of an object.
B.) Frictional force is parallel to the surface in contact.
C.) Frictional force always produces heat
D.) Frictional force can be increased or reduced

Answer 1

Hint: Friction is a force which always opposes the motion of an object and it acts in the opposite direction of the motion. Due to friction heat is also produced.

Complete step-by-step answer:
Friction is defined as the force which opposes the motion of an object on the surface it is in contact with. It makes it easy to walk on the roads without slipping which is an advantage for us also in moving heavy objects, it becomes difficult because of the friction which is against us.

Types of friction static friction, rolling friction, sliding friction, and fluid friction.

Friction exists when the two surfaces that are in contact with each other are having irregularities on them. These irregularities get interlocked making friction come into the picture. Therefore, it can be said that friction is dependent on the roughness and smoothness of the surface.

Advantages of friction:
1.) Friction between the feet and the ground makes it easy to walk and run on the ground without falling.
2.) Writing on paper or on the board becomes easy because friction exists between the pen and paper or the board.

Disadvantages of friction:
1.) Friction leads to wear and tear of the moving parts in machines and soles in shoes.
2.) Heat is produced during friction which is a waste of energy in machines.
3.) Friction can be increased or decreased with the help of lubricants such as castor oil and grease which helps in reducing the friction and they are used in machines to reduce the wear and tear of the surfaces that are in contact and also, they make the working smooth. Friction between these objects and the surface can be increased by making grooves and treading in the objects.

It can be said that depending on the situation, friction can be considered to be evil or not.

Now when we will try to understand each option given, we will observe that

Frictional force always opposes the state of motion of an object -as we know that friction is a force that always opposes motion of an object because it always acts in a direction exactly opposite to that in which an object is moving and stops when the surface rubs or drags against another surface.

Frictional force is parallel to the surface in contact. As we know normal force is always perpendicular to the surface and frictional force is always parallel to the surface in contact.

Frictional force always produces heat-as we know that due to increase in internal energy of the molecules which interact with each other and hence the electrons create a radiation due to which heat energy is produced as a result the frictional force produces heat.

Frictional force can be increased or reduced – we know that frictional force can be increased by increasing the normal force and can be decreased by applying lubricants.

Hence all the given options describe the frictional force. Therefore, all the options are correct.

Note: Friction is very important for us in our everyday life. It is both favourable and unfavourable for us but in both the parts it is very important. If friction is not present then we can’t even think of walking. Therefore, we must always remember the properties of this force.