In many teaching exams including REET 2021STET 2021 etc. Science may be an interesting subject having 15 questions of Science content and 15 questions of Science Pedagogy in REET and other State TET Exams. Science comprising of various branches of studies like chemistry, physical science, and life science.
Have you ever wondered how a rolling ball eventually comes to a halt? Why is it that we cannot hold a glass firmly when our hands are oily? Why do our shoes get worn out after some days of use? Why are there wheels attached to luggage trolleys? Why do we tend to slip on a wet floor? These are due to ‘Friction’. In this chapter, we will study Friction and its characteristics.
The Force of Friction
Friction is a type of force that opposes motion. It is that force that always acts in a direction opposite to that of the applied force. In the case of a ball freely rolling on the ground, the ball eventually comes to stop, because of the force of friction that acts between the ball and the ground. When the rowing of a boat is stopped, the boat eventually comes to a halt because of friction. It also means that while rowing the force should be greater than the force of friction.
Factors affecting Friction: –
As we studied in the previous case, friction is caused by the interaction between the surfaces which are in contact. Friction is caused by the irregularities on the two surfaces which are in contact. The irregularities on both surfaces tend to lock into each other and this resists the motion of the object. The nature of the surface (smoothness or roughness) affects the friction.
- Smooth surfaces have lesser irregularities. The lesser the irregularities, the lesser the tendency to lock. The lesser the tendency to lock with another object, the lesser the friction (that is tendency to oppose motion). And so, a ball rolls faster and covers a greater distance on a smooth surface such as a marble floor or a wet floor. Think of the bowling game.
- Rough surfaces have more irregularities. The more irregularities, the more tendency to lock. The more the tendency to lock, the more friction (that is tendency to oppose motion). And so, a ball rolls slowly and covers a lesser distance on a rough surface such as a muddy playground. Think of a rough muddy playground. So, it obviously means that to get the ball rolling we have to apply a force that is greater than the frictional force offered by the ground.
This also explains why we cannot hold a glass with oily hands. Our hands are greasy and smooth and we know that smooth offers lesser interaction or lock with the glass. And hence it tends to slip. While trekking on hilly and watery terrains, we wear groovy sports shoes so that rough shoes establish better locking with the hilly trains, increase friction, provide more grip and decrease chances of a slip.
Friction-a Necessary Evil
- Desirable Friction – Grooves on Tyres
- Undesirable Friction – Worn outsoles
|Desirable Friction||Undesirable Friction|
|These are the instances where friction exists and is absolutely essential.||These are the instances where friction exists, but it is undesirable.|
|· Such type of friction should be retained or increased||· Such type of friction should be minimized|
(Note: As we can see again, rough surfaces increase friction. Smooth surfaces decrease friction.)
Methods to reduce friction: –
We mentioned above that undesirable friction should be reduced. Here are some of the ways to reduce Friction.
- Lubricants: In the case of automobiles and machine – parts that tend to get screechy or ineffective over a period of time, we apply substances to make their surfaces smooth and thereby reduce friction. These are called lubricants. You must have seen specific lubricants for automobile parts in petrol stations. Also, you must have noticed that we apply oil to screechy doors in our houses.
- Wheels: We have seen luggage trolleys use wheels. It is easier to pull heavy loads with wheels as against pulling/pushing them along the ground.
Try pulling or pushing a heavyweight object/ luggage without wheels on the ground and you will realise it would be much harder. This is because of the friction offered by the ground on the heavy load. This opposition to motion when a body moves over another surface is called Sliding Friction. But with the wheel, it just rolls. This opposition to motion when a body rolls over another surface is called Rolling Friction. The Rolling Friction is less than Sliding Friction.
Friction also produces heat: –
- The friction between a match stick and matchbox helps light the match stick and so.
- When you rub your palms together for a few seconds, they become warm
Fluid Friction: –
Fluids (means liquids and gases) exert friction on the objects. The frictional force exerted by fluids is called drag. Since water and air exert friction on the bodies that move in them like the boat, fish (in water), aeroplane and birds, their physical structure should be such that they can oppose this friction and move forward.