Chapter 9 – Friction

Chapter 9 – Friction

 

1. What is Friction? (What is Friction?)

• Friction is a force that always opposes the relative motion  between two contact surfaces.
• It always acts in the opposite  direction of the direction of motion.
• Example: If you push a book to the right on the table, the frictional force will apply to the left.

 

2. Factors Affecting Friction

Friction depends on the following factors:

1. Nature of Surfaces:

• • The more rough surfaces, the greater the friction.
  • The smoother the surfaces, the less friction.
  • When viewed under a microscope, there are some irregularities on all surfaces. These irregularities get trapped in each other, leading to opposition to motion.

1. Force Pressing the Surfaces Together:

• • If two surfaces are pressing on each other with more force, the friction will increase.
  • Example: More friction is felt if you try to push a heavy box.

 

 

 

 

3. Types of Friction

Friction is mainly of three types:

1. Static Friction:

• • This friction acts when an object  is at rest and an attempt is being made to move on it, but it does not move.
  • It is present just before the movement starts.
  • It is the force required to prevent an object from shifting.
  • Example: Trying to move a heavy box but it won’t move.

1. Sliding Friction:

• This friction acts when one object is sliding over the surface of another object.
• Sliding friction is less than static friction . This is why it is easy to maintain an object once it is in motion.
• Example: Rubbing a matchstick on a matchbox, sliding it on a slide.

iii.  Rolling Friction:

• This friction acts when one object is rolling on the surface of another object.
• Rolling friction is less than sliding friction .
• This is why the wheels are easy to use and it is easy to accelerate in roller skates.

4. Friction: A Necessary Evil

Friction is useful to us in some situations and harmful in some situations.

•  Advantages of Friction:
  • Walking and running: without friction we would slip.
  • Writing: Pens and pencils are able to move on paper only due to friction.
  • Movement and stopping of vehicles:  The friction between the tyres and the road causes vehicles to move and stop. Brakes work only because of friction.
  • Grip Objects: Friction helps us to grip objects.
  • Burning a match: Fire is caused by friction.
  • Hammering nails:  The nail rests in the wall due to friction.

 Disadvantages of Friction:

• Waste of Energy: Energy is wasted in the form of heat due to friction.
•  Wear and Tear: Machine parts wear and tear due to friction.
• Inefficiency: The efficiency of machines is reduced.
• Generating heat: Excessive heat can be generated in machines.

5. Increasing and Reducing Friction

•  Increasing Friction:
  •  Treads of Tires: Grooves are made in the tyres of vehicles to provide a better grip on the road and increase friction.
  •  Soles of Shoes:  The soles of shoes also have grooves to make it easier to walk.
  • Sports Shoes: Sportsmen’s shoes have spikes.
  • Kabaddi players: Rub mud on their hands so that the grip is strong.
  • Brake pads of vehicles: These prevent the vehicle from the force of friction.

 Reducing Friction:

•  Lubricants:  Materials such as oil, grease, or graphite are placed between moving parts of machines to reduce friction.
•  Using Wheels: By using wheels we convert sliding friction into rolling friction, which makes motion easier (rolling friction is less than slid friction).
• Ball bearings: Ball bearings  are used in bicycles, cars, and other machines. These slid frictions are converted into rolling friction, thereby reducing the wastage of energy.

6. Liquid abrasion /friction Fluid Friction drag)

• Fluids (such as air and water) also exert frictional forces on objects that pass through them.
• This frictional force is  called  drag or  fluid friction.
• Objects moving at very high speeds in the air, such as airplanes, are specially shaped in such a way that air friction is minimized. This process is  called  streamlining.