Friction #2 (Let's Learn Series #23 - Physics) | Ecency

Hello dear learners, last day, you learnt the three types of friction that acts on an object. You can check it here. So today, you are going to learn the factors which affect Friction.

Let's do an activity to see whether the limiting frictional force depends on the nature of the two contact forces.

You'll need,

a block of wood
Newton balance
sand papers of various roughness

First keep the block of wood on a table and measure it's limiting frictional force. (instance 1)

Now, attach the sandpaper with the lowest roughness and measure the limiting frictional force. (instance 2)

Now do the same with a sandpaper with higher roughness and measure the limiting frictional force. (instance 3)

Now compare the measurements you got. You will see that the limiting frictional forces will be like this.

instance 1 < instance 2 < instance 3

The limiting frictional force in the 1st instance is less than the 2nd instance and the limiting frictional force in the 2nd instance is less than the 3rd instance.

∴ we can conclude that the limiting frictional force depends on the nature of the two surfaces in contact.

Let's do an activity to see whether the limiting frictional force depends on the weight of the object.

You'll need,

3 blocks of wood
Newton balance

Keep one block of wood on a table and measure its limiting frictional force. (1st instance)

Keep another block of wood on that block of wood and measure its limiting frictional force. (2nd instance)

Keep another block of wood on that block of wood (now there are 3 blocks of wood on each other) and measure its limiting frictional force. (3rd instance)

When you compare the limiting frictional forces in the three instances,

1st instance < 2nd instance < 3rd instance

The limiting frictional force in the 1st instance is less than the 2nd instance and the limiting frictional force in the 2nd instance is less than the 3rd instance.

∴ we can conclude that the limiting frictional force depends on the weight of the object.

Let's do an activity to see whether the limiting frictional force depends on the surface area of the contact surface.

You'll need,

cuboid shaped wood
Newton balance

Mark the three different surfaces with different surface areas as A, B and C.

Keep the side A on the table and measure its limiting frictional force. (1st instance)

Keep the side B on the table and measure its limiting frictional force. (2nd instance)

Keep the side C on the table and measure its limiting frictional force. (3rd instance)

When you compare the measurements you got,

1st instance = 2nd instance= 3rd instance

The limiting frictional forces in the three instances are same.

∴ we can conclude that the limiting frictional force does not depend on the surface area of the surface in contact.

When do you use Friction?

Do you use frictional forces in your daily life? Of course you do.

Sometimes we increase friction and sometimes we decrease friction.

Instances which you increase friction.

Grooves are etched on tyres so that the tyre doesn't slip on the road and on rainy days, the water can go through the groove so that the vehicle doesn't skid.

Source

We can walk because of friction. In instances where friction is reduced such as an oily surface, you can't walk.
In coir ropes a number of coir fibres are twisted on each other and they can't be easily separated because of the high frictional forces.

How to reduce Friction?

Reducing the roughness in surfaces in contact by polishing them.
Applying lubricants like graphite and grease or lubricant oil to reduce roughness in surfaces in contact.
Inserting balls that roll between the contact surfaces.