• Friction can be defined as the type of force that resists the movement of objects when their surfaces come in contact with each other.
• It can be of three types: static, sliding and rolling friction.
• The magnitude of rolling friction is the lowest, and the static friction is the highest.
• Friction is more on a rough surface and less on a smoother surface.
• Friction is necessary for basic activities like writing, walking, running, holding an object etc.
• Friction can be reduced by applying oil or any smoother substance over the surface of an object.

## Types of Friction

### Why Are Two Wheels Attached to This Chair?

• The picture shows a wheelchair used to carry old or sick people.
• This chair needs to be dragged.
• Adding wheels to the chair's base reduces the friction between the chair and the ground and makes it easy to drag the chair.

### In Which Directions Friction Force and Motion Work, Explain With an Image.

• Motion and friction force act in directions opposite to each other.
• If a vehicle moves towards the east, the frictional force will act in the west.

### Why Do Aquatic Animals Have Streamlined Bodies?

• Aquatic animals like fish, whales, and dolphins have streamlined bodies.
• Ocean and river water exert fluid friction on the bodies of aquatic animals.
• A streamlined body is tapered at both ends, which helps in reducing friction and hence swimming in a better manner.
• For the very same reason, boats and ships are streamlined in shape.

### What Is Dry Friction?

• The frictional force that comes into action when two solid bodies come in contact with each other is called dry friction.

### Why Do Aeroplane Wheels Sometimes Show Sparks While Landing on the Runway?

• A runway is made of concrete. When aeroplanes land, their wheels touch the surface of the runway first.
• Due to the high speed of the aeroplane, static electricity is produced as a frictional force acts due to contact between the surface of the wheels and the runway.

### Reshma Was Running on the Wet Floor, and Suddenly She Slipped. Why Do You Think It Happened?

• Friction helps us to stand, run or walk on the floor.
• Due to wetness on the floor, the friction gets reduced, which may lead to slipping or difficulty in walking or standing.
• Reshma slipped on the wet floor due to reduced friction because of the presence of water.

### Dhriti Is the Class Monitor. She Is Told to Clean the Blackboard. By Mistake, Dhriti Cleaned the Blackboard With Water. Now the Teacher Cannot Write and Said That She Has to Wait for a Few More Minutes- Why Did the Teacher Say So?

• Friction plays a role while writing on a blackboard or paper.
• The blackboard, when cleaned with water, became smoother, which led to the reduction of friction.
• Since the surface got smoother, the teacher could not write on it with chalk. She suggested waiting as the blackboard would not be as smooth once the water dries off completely.

### Identify the Types of Friction in the Following Images.

1. Static friction.
2. Sliding friction.
3. Sliding friction.
4. Fluid friction.

### Why Is Oil Applied to the Window and Door Hinges?

• The oil acts as a lubricant.
• Oil is applied on the hinges of doors and windows to reduce friction.
• Without lubricants, the hinges do not work correctly due to increased friction. Also, they wear and tear after a short period.

### Why Is Oil Applied to the Window and Door Hinges?

• Anti-skid tiles have a rough surface which helps in increasing the friction even when the surface is covered with water.
• This helps to prevent accidental slips on the wet bathroom floor.

### Why Can an Object Dipped in Honey Not Move Faster Than an Object Dipped in Water?

• The fluid friction exerted due to the presence of a fluid depends on the viscosity of a liquid.
• Viscosity is the property of fluid by which it opposes the motion between its different layers.
• The Higher the density, the higher is the viscosity.
• Since honey is thicker and denser than water, it produces more fluid friction, making the movement difficult.

### When Kicked on an Elevated Land and Football Field, Football Simultaneously Took Different Times to Cover the Same Distance. State the Reason for the Same.

• In both cases, football experiences different types of friction.
• While moving on elevated land, it experiences sliding friction.
• Whereas static friction plays a role on a flat surface.
• The magnitude of sliding friction is lesser than that of static friction.
• Hence the ball takes less time to cover the same distance on elevated land than on a flat surface.