Olympiad Science - Friction
Exam Duration: 45 Mins Total Questions : 30
What type of a force is friction?
- (a)
Contact force
- (b)
Non-contact force
- (c)
Electrostatic force
- (d)
Magnetic force
Frictional force is always between two surfaces in contact with each other.
What is the value of sliding friction for an object which requires 7 N of force to move it from rest?
- (a)
7 N
- (b)
Greater than 7 N
- (c)
Less than 7 N
- (d)
14 N
Sliding friction is less than the friction that builds up before sliding, i.e., static friction. Hence, sliding friction is less than 7 N.
Which of the following reduces friction in a rotating machine?
- (a)
Wheels
- (b)
Rollers
- (c)
Ball bearings
- (d)
Handle
The use of ball bearings causes rolling friction which is much less than the sliding friction.
Why is a carrom board usually powdered before playing?
- (a)
For increasing friction
- (b)
For decreasing friction
- (c)
For decoration
- (d)
For fragrance
Powder is a lubricant and reduces friction. Hence, for decreasing friction, carrom board is usually powdered before playing
What is the frictional force exerted by fluids called?
- (a)
Lift
- (b)
Drag
- (c)
Rolling friction
- (d)
Dynamic Friction
The frictional force exerted by fluids is called drag.
Why are certain bodies streamlined?
- (a)
To increase friction
- (b)
To decrease weight
- (c)
To reduce friction
- (d)
To increase weight
A streamlined body reduces drag (friction) during motion.
In the decreasing order of magnitude, which of the following is correct?
- (a)
Rolling < static < sliding friction
- (b)
Static> sliding> rolling friction
- (c)
Static> rolling> sliding friction
- (d)
Sliding < static < rolling friction
For the given surfaces static friction is somewhat greater than sliding friction as well as rolling friction. It is easier to roll than to slide. Hence, sliding friction is greater than rolling friction. The decreasing order of magnitude of friction is static, sliding and rolling.
Which of the following activities is easier to perform on a drum of 10 kg?
- (a)
Dragging the drum
- (b)
Lifting the drum
- (c)
Rolling the drum
- (d)
All of the above need the same effort
Rolling friction is much less than sliding friction. So, rolling a drum is easier.
Why does a meteor burn upon entering the earth's atmosphere?
- (a)
Due to gravitational pull
- (b)
Due to the heat of the earth
- (c)
Due to solar radiation
- (d)
Due to excess friction in air
Due to the very high speed of meteor when it enters the earth's atmosphere, the heat produced by the friction of air is very large which causes the meteor to burn.
Why are the head of a match stick and the sides of a match box deliberately made rough?
- (a)
To increase friction
- (b)
To decrease friction
- (c)
To increase the amount of heat
- (d)
To decrease the amount of heat
due to increased friction, greater frictional heat is produced in the match stick which thus lights up easily.
Why are spikes provided in the shoes of athletes?
- (a)
As a decoration
- (b)
To increase friction
- (c)
To decrease friction
- (d)
To give shape
Spikes in the shoes increase friction and prevent slipping.
Which force prevents us from slipping while walking on the road?
- (a)
Muscular force of our body
- (b)
Gravitational pull by the earth
- (c)
Frictional force
- (d)
Balanced forces of nature
When we push the ground with our feet, the friction provides a forward reaction to our push and makes us move forward. (Walking on slippery ground is difficult because the frictional force is not enough to prevent slipping).
What will happen to a moving object if there is no friction?
- (a)
The object will stop.
- (b)
The object will keep on moving.
- (c)
The object will change speed.
- (d)
The object will change direction.
Friction opposes the relative motion of objects. In its .absence. a moving object will not stop.
Which of the following is NOT an effect of frictional force?
- (a)
The grooves of tyres flattened due to use
- (b)
A rolling ball coming to a halt
- (c)
Leaves falling from a tree
- (d)
The holding of a pencil
Leaves falling from a tree onto the ground is due to the effect of gravitational force and not due to frictional force.
Why are tyres made circular in shape?
- (a)
It is easy to inflate circular tyres.
- (b)
Rolling friction is less than sliding friction.
- (c)
Circular tyres dissipate less heat.
- (d)
Circular tyres easily slow down or stop a vehicle.
Since, rolling friction is less than sliding friction, the tyres are made circular instead of flat.
A coin flicked on a table will stop. Why?
- (a)
It is heavy
- (b)
No force is acting on it
- (c)
The earth attracts the coin
- (d)
The table exerts a frictional force
The coin will stop because of friction exerted by the surface of the table on the coin.
While walking on ice, why should one take small steps to avoid slipping?
- (a)
Smaller steps ensure larger friction
- (b)
Smaller steps ensure smaller friction
- (c)
Smaller steps ensure larger distance covered
- (d)
Smaller steps ensure smaller distance covered
While walking on ice, one should take small steps to avoid slipping as smaller steps ensure larger friction.
In which of the following activities is friction useful?
- (a)
Driving a car
- (b)
Sitting on a chair
- (c)
Rowing a boat
- (d)
All of the above
It will be difficult to sit on a chair without friction. In the other two cases too, friction is useful.
Which of the following is a measure of the force required to keep an object moving with the same speed?
- (a)
Static friction
- (b)
Sliding friction
- (c)
Limiting friction
- (d)
All of the above
Sliding friction is required to keep the object moving with the same speed. Once the applied force overcomes the static friction, the object starts moving.
Which of the following activities will not be possible in the absence of friction?
- (a)
Holding a glass
- (b)
Writing on a paper
- (c)
Sitting on a chair
- (d)
All of the above
Holding a glass, writing on a paper and sitting on a chair are the activities which are not possible without friction.
Which of the following activities will produce the least amount of frictional force?
- (a)
Walking
- (b)
Running
- (c)
Ice-skating
- (d)
Rowing a boat
Ice offers the least friction as compared to water and road surfaces.
Which of the following is reduced by the correct measure of air pressure in the tyres?
- (a)
Static friction
- (b)
Sliding friction
- (c)
Rolling friction
- (d)
All of the above
The correct measure of air pressure in the tyres provides an air cushion to reduce rolling friction.
Which of the following makes it difficult to quickly stop a ship moving in a sea by applying brakes?
- (a)
Low friction
- (b)
Excess friction
- (c)
High speed
- (d)
External force
Friction exerted by water is much less than that exerted by a solid. Hence, it takes more time to stop a ship in water.
When a coin and a feather are dropped simultaneously from the same height, the coin strikes the ground first. Why?
- (a)
Gravitational force is less in the case of the coin.
- (b)
Mass of coin is less.
- (c)
Frictional force is less in the case of the coin.
- (d)
Magnetic force is stronger in the case of the coin.
Due to larger surface area, the feather faces more air resistance (friction by air) and hence slows down, while the coin moves faster and touches the ground faster.
Why do the soles of our shoes easily wear out?
- (a)
Due to the difference in the material of the sole
- (b)
Due to poor design
- (c)
Due to friction
- (d)
Due to their size
When we walk on the road, the friction between the soles of our shoes and the road wears out the soles.
Harish rolled a small steel ball at one edge of the glass bowl as shown below,
If there is no friction between the surfaces of the ball and the bowl, what will happen to the ball?
- (a)
The ball will roll out of the glass bowl near edge 'Q'.
- (b)
It will stop at centre point 'R' after a number of to-and-fro motions.
- (c)
It will keep moving between point 'P' and 'Q' and will never stop.
- (d)
It will not move at all since friction is required for movement.
In the absence of friction (no opposing motion). a moving object will keep on moving. In this case, the ball will oscillate between points 'P' and 'Q' due to the action of gravitational force.
Look at the figure given below.
Which of the following forces is necessary for a person to climb the mountain?
- (a)
Gravitational force
- (b)
Electrical force
- (c)
Frictional force
- (d)
Magnetic force
A person will not be able to climb a mountain if frictional force i.e., a contact force is absent.
Observe the figure given below.
Identify X and Y.
- (a)
X Y Motion Weight - (b)
X Y Motion Friction - (c)
X Y Friction Weight - (d)
X Y Weight Motion
Frictional force is the relative force between two surfaces in contact. The motion of body X will be in the direction of pushing force. Frictional force Y acts in a direction opposite to the direction of motion.
In which of the following does friction playa helpful role?
(i) Striking a match stick
(ii) Playing snooker
(Hi) Writing on the blackboard
- (a)
Only (i) and (ii)
- (b)
Only (ii) and (iii)
- (c)
Only (i), and (iii)
- (d)
(i), (ii) and (iii)
Friction plays an important role in the striking of a match stick, playing snooker and writing on the black board.
Which of the following shows that friction exists between the two bodies?
- (a)
When the movement is decreased or prevented
- (b)
When there is a constant movement
- (c)
When electromagnetic charges are produced
- (d)
When there is a constant increase in weight
Friction is the relative force between two surfaces in contact, which causes the decrease in the movement of a body or sometimes may even prevent the motion.