Merits and demerits of friction and methods to reduce it - class-IX

Powder acts as a lubricant to the surface and reduces friction so that the game can be carried on smooth surface.

Powder is a lubricant because it reduces the friction and makes the surface smooth.

Oil is the best and the most commonly used lubricant used for keeping machines running smoothly and to avoiding wear and tear of machines as it reduces the friction more effectively.

A vehicle skids on the road due to less friction between the road and the vehicle tyres.

Lubricants reduce the rounghness of an surface and make them smooth. Smooth surfaces have less friction due to reduced roughness.

Rough surface is uneven so it provides more resisitance to motion of a body hence the frictional force increases.

When we push the ground with our feet, the friction provides a forward reaction to our push and sends us forward. Walking on smooth ground is difficult because the frictional force is not great enough to prevent slipping.

Answer is B.

Brakes is a type of automotive brake that slows or stops a vehicle by converting kinetic energy into heat energy, via friction. The heat energy is then dissipated into the atmosphere. 
Hence, braking of a vehicle happens due to friction.

Answer is B.

Spikes are provided on the soles of shoes of athletes to increase the friction between the shoe and the ground.

Answer is A.

A match is a small stick of wood or strip of cardboard with a solidified mixture of flammable chemicals deposited on one end. When that end is struck on a rough surface, the friction generates enough heat to ignite the chemicals and produce a small flame. Some matches, called strike-anywhere matches, may be ignited by striking them on any rough surface.
Hence, the surface of the head of a matchstick and sides of a match box are deliberately made rough to increase friction.

Answer is D.

Efficiency is relate to energy conversion performance. A system that can convert energy entirely and completely into energy of another form performs the conversion at 100% efficiency. 
The heat produced by friction cannot be used to recover 100% of the mechanical energy that was converted into heat, the effect of friction is to reduce the (energy conversion) efficiency of machines. 
The parts of the machine wear and tear due to contimuous usage.
More the friction more the enrgy consumption.
Hence, all the options are correct.

Friction is responsible for wear and tear of machine parts.
Friction is the main force that is responsible for the wear and tear of machinery, this is why mechanical parts are sometimes oiled, to minimize the friction present.

We will need friction to roll or run on any surface. In our case, we have a frictionless surface. Hence, by conservation of linear momentum sneezing can make us move on that surface.

When friction is present, there is a loss of energy. Since frictional force have done work and the energy is lost. Due to this frictional force is released in the form of heat energy.

The irregularities between the paper and the pen or pencil create friction. Due to friction, the particles of ink or lead stick to the paper and get locked in its irregularities. If there would be no friction between the paper and pen or pencil, the ink/lead would not stick to the paper and we would not be able to write.

Friction is important to perform many tasks. It also produces heat in the process and since the two surfaces keep rubbing against each other, they gradually wear out.

Friction helps to lock the two surfaces in contact. 

Friction is both desirable and undesirable depending on the situation. For example, the tyres of an automobile are grooved to increase friction. However, the ball bearings in the same automobile are regularly oiled to reduce friction and ensure smooth functioning of the engine.

Friction comes into play when two irregular surfaces come in contact. The continuous rubbing of these surfaces together causes it to gradually wear out. Also, much of the applied force or energy is wasted in overcoming the force of friction. Hence, it is considered as evil, but it is necessary too.

The friction is a force which occurs between two bodies, when say one of them is at motion/ or at both of them in a motion. The rubbing of hand is an example of friction which causes warm feeling in hands.

Our shoes encounter wear and tear due to friction. 
We are able to walk due to friction.
Friction resists us from sliding.

Friction is necessary in our daily life. But it is an evil as it causes heating and wear and tear. So, it is a necessary evil.

A car moves forward due to friction and also can be controlled on road due to friction. In winter, due to morning dew, friction decreases and the  driver has to be careful. Due to presence of dew, friction in winter is less than that in summer.

Lifting is not a type of friction. All others are types of friction.

All of the above is correct answer. As we know friction is useful but in other means it is also disadvantageous or we can say an evil which is a necessity. Whenever there is movement between two parts of machinery or whenever there is contact between shoes sole and rough road, the parts in contact wear out. Friction causes wear and tear of parts as well as heat is produced which damages the parts.

The statement that friction is not useful, is not true. Friction is advantageous in our daily life. Without friction we will not be able to walk properly, nor drive vehicles etc. 

Frictional force can help a car to slow down and can help to move around the corners without skidding due to the frictional force between tyres and ground . Without friction , brakes of the car will not work and it will be impossible to control the car , due to this we say friction is a necessary evil .

Friction force is the force that opposes the relative motion of an object or the direction opposite to the tendency of relative motion due to the contact of 2 rough surfaces. Hence it is exactly opp to the direction of relative motion of the object.

Friction is essential for movement (walking, driving, etc.). Without it, we would slip constantly, making life very difficult, not easy. Statement II is a correct physical fact regarding ground reaction forces.

ADVANTAGES OF FRICTION
Friction plays a vital role in our daily life. Without friction we are handicap.
1. It is becomes difficult to walk on a slippery road due to low friction. When we move on ice, it     becomes difficult to walk due to low friction of ice.
2. We can not fix nail in the wood or wall if there is no friction. It is friction which holds the nail.
3. A horse can not pull a cart unless friction furnishes him a secure Foothold.
DISADVANTAGES OF FRICTION 
Despite the fact that the friction is very important in our daily life, it also has some disadvantages like:
1. The main disadvantage of friction is that it produces heat in various parts of machines. In this way     some useful energy is wasted as heat energy.
2. Due to friction we have to exert more power in machines.
3. It opposes the motion. 
4. Due to friction, noise is also produced in machines.
5. Due to friction, engines of automobiles consume more fuel which is a money loss.
So, Friction is useful for braking moving vehicles; for walking in smooth / slippery surfaces like snow and sand.
Answer (D) friction is harmful

By spitting or sneezing we can get off.

1. Static friction is considered a self adjusting force because it wants the object to remain at rest and not move. Therefore, if an external force is applied, the static force will be equal to the magnitude of external force, until it surpasses the threshold of the motion. Hence friction is a self-adjusting force.
2. If there is no friction between any two surfaces in contact , then we will not be able to walk properly on the earth. Hence friction is necessary, But too much friction will reduce the efficiency of machines. Hence friction is a necessary evil.
3. Friction allows us to hold anything, pick up anything , allows us to go anywhere . Same goes with riding a car or a bike. Thus friction is important force in our daily life.

The friction can be avoided when the contact surface is smooth. But for a rough contact surface, the friction opposes the motion. Thus the given statement is false.

Friction is the force that resists motion when the surface of one object comes into contact with the surface of another. In a machine, friction reduces the mechanical advantage , or the ratio of output to input an automobile, for instance , uses one-quarter of its energy on reducing friction. Hence the efficiency of machine is reduced due to friction.

When the pin is removed, the sphere continues rolling without slipping because friction between the sphere and upper plank surface prevents relative motion. Since the lower surface of plank P is smooth and there's no external horizontal force on the sphere-plank system, the center of mass has no horizontal acceleration. The plank remains stationary as the sphere maintains its rolling motion.