Friction

The force of friction comes into play irrespective of the states of matter.

⇒ The force of friction does not depend upon the state of matter of any particular object.

⇒ Force of friction acts in solids, liquids and gases.

In the figure, a boy is pushing the box from right to left, this mans the force of friction will act on the box from left to right.

⇒ The force of friction always opposes the applied force.

⇒ If you apply the force along the left, friction acts along right.

⇒ If you apply the force along the right, friction acts along left.

To sharpen the blade of a knife, rubbing it against the surface of a stone will be the most suitable.

⇒ Friction increases when the surface is rough.

⇒ Stone has rough surface among all.

⇒ When you rub the knife against it, it will exert greater reaction.

⇒ As a result, the force of friction will increase and the knife will become sharper.

A toy car released with the same initial speed will travel farthest on cemented surface because:

⇒ A cemented surface has least frictional force.

⇒ As a result, force of friction does not act and will not oppose the motion of toy car.

⇒ Thus, it will travel farthest on cemented surface.

The friction will decrease on applying oil on door hinges because:

⇒ When oil is applied between the moving part of a door, a thin layer is formed there.

⇒ Due to which the moving surfaces do not directly rub against each other.

⇒ As a result, friction reduces and the movement of door becomes smooth.

Note: The substances which reduce friction are called lubricants. For example – oil, grease, graphite etc.

Friction will act on a ball moving through air. Force of friction applies everywhere, whether it is along the ground, on water, on a smooth road or through the air.

By sprinkling talcum powder on the wooden surface, the ball will cover longer distance because:

⇒ Talcum acts as a lubricant.

⇒ It reduces the force of friction.

⇒ Due to which the ball will cover longer distance.

Paheli is least likely to slip on gravel surface because:

⇒ The surface of gravel is rough.

⇒ Friction increases when a surface is rough.

⇒ Thus, there will be enough force of friction for her to walk easily without getting slipped.

The second block having mass 2 units would require a larger force to move it from the rest position because:

⇒ As the mass of the object increases, the force of friction increases.

⇒ Hence, second block (mass 2units) will be having more force of friction.

⇒ Thus, it need larger force to move the heavier block from the rest position.

Yes, the force of friction comes into play when a raindrop rolls down a glass window pane. The force of friction always takes place when two surface comes in contact. Here one is raindrop’s surface and other is glass window pane’s surface.

The boy having bicycle with old tyres is more likely to skid on the oily road because:

⇒ The old tyres will experience less friction in comparison to that of new tyres.

⇒ To move on the oily road needs larger force of friction.

⇒ But the old tyres have less friction which is not enough to move on the oily road.

⇒ Thus, it is most likely to skip.

No, the box will not experience any force of friction because the force applied by both the boys is equal. Thus, the net (total) force on the box will be zero. As a result, there will be zero force of friction.

No the object will not experience any force of friction because force of friction takes place only when two surface comes in contact.

It is given that the object does not touch the walls of the tube thus, there will be no force of friction.

When used for a long time, slippers with rubber soles become slippery because:

⇒ For a given pair of surfaces, friction depends upon the smoothness of those surfaces.

⇒ Due to continuous rubbing of slippers with the ground, the rubber soles(surface) of slippers becomes smooth.

⇒ As we know that friction decreases when a surface is smooth.

⇒ As a result, friction decreases between rubber sole and the ground.

⇒ Thus, slippers become slippery.

Yes, there is a force of friction between the wheels of a moving train and iron rails because both the surfaces are in contact.

⇒ The type of friction present is rolling friction.

Note: When one body rolls over the other surface of another body, rolling friction into play.

⇒ If an aircushion is introduced between the wheel and the rail, the force of friction decreases because now there is no contact between wheels and rails.

Cartilage is present in the joints of our body which helps in reducing the friction and causes a smooth movement. As the age increases, the cartilage become less effective.

⇒ Due to which the force of friction increases.

⇒ As the force of friction increases, means that smoothness of movement decreases.

⇒ As a result, the movement of joint become difficult which leads to pain in joints.

While playing tug of war, Preeti felt that the rope was slipping through her hands. To prevent this, first she need to make her smooth hand non-smooth.

⇒ Because the friction decreases as the surface becomes smooth. Hence, the rope was slipping through her hands (smooth).

⇒ To make her hands non-smooth, she should apply sand on both the hands.

⇒ Due to the sand, her hands become non-smooth (rough)

⇒ Friction increases when the surface is rough.

⇒ As a result, friction increases between the rope and her hand and now the rope won’t slip through her hands.

The handle of a cricket bat or badminton racquet is usually rough because:

⇒ As we know that the force of friction increases as the surface is rough.

⇒ The surface of bat or badminton racquet is rough, therefore it does not slip away through the hands.

⇒ As a result, there will be a better grip between handle of the bat and hands due to increased friction.

The surface of mortar and pestle used for grinding is etched again after prolonged use because:

⇒ The mortar and pestle lose their roughness after prolonged use (using for long time).

⇒ As a result, the force of friction decreases and they do not grind properly.

⇒ So they are etched to make them more effective for grinding again.

The marble will move the shortest distance on the layer of sand because the silk cloth and glass sheet will exert lesser maximum friction whereas the sand (being more rough) exert maximum friction against the motion.

We need to apply larger force to move the car (heavier object) from its rest position. As the mass increases, the force of friction increases.

⇒ Once the car starts moving, the friction becomes rolling friction. Rolling reduces friction. Thus, the force applied now is less than the previous one.

⇒ So, to keep the car in motion and balanced, we only need to exert the lesser force.

When the cutting edge of a knife is put against a fast rotating stone to sharpen it, sparks are seen to fly because:

⇒ The friction increases between the edge of knife and rotating stone.

⇒ As a result, it increases the temperature of the knife and stone

⇒ Friction produces heat.

⇒ As the friction is very large in this case, thus the temperature increases to such a level that the sparks are produced.

The one rubbed with sand paper shines more than the other because:

⇒ When the metal sheet is rubbed with sand paper, it produces more friction between metal sheet and sand paper.

⇒ As a result, the force is enough to remove easily all the dust particles present on metal sheet, so it shines more.

⇒ On the other hand, when the metals sheet is rubbed with ordinary paper, it does not produce enough force of friction to remove dust particles.

⇒ Thus, the metal sheet rubbed with ordinary paper shines less.

If the seat cover is very smooth, we tend to slip when brakes are applied suddenly because:

⇒ As we know that the friction decreases when the surface is smooth.

⇒ The seat cover of a rickshaw is smooth, this means the friction between the body and the seat is lesser.

⇒ Thus, when the brakes are applied suddenly, we tend to slip due to decreased friction.

By using rollers below the heavy load can make the task easier for them:

⇒ Rollers (wheels) reduce friction.

⇒ It is always easier to roll than to slide a body over another.

⇒ Thus, it is convenient to push the heavy load fitted with rollers.