Detailed answers for important examination questions.
01
State the effects of a force on a stationary body and a moving
body.
Subjective question
A force can affect both stationary and moving objects.
Effect on a stationary body:
It can make the stationary object start moving.
It may also change the shape or size of the object.
Effect on a moving body:
It can increase or decrease the speed.
It can change the direction of motion.
It can stop the object completely.
It may change the shape or size of the object.
Therefore, a force can change the state of motion, speed,
direction or shape of an object.
02
Distinguish between a contact force and a non-contact force.
Subjective question
Contact Force
Non-contact Force
It acts only when two objects are physically touching.
It acts without physical contact between the objects.
It needs direct interaction between surfaces.
It can act over a distance.
Examples include frictional force and muscular force.
Examples include gravitational, magnetic and
electrostatic force.
03
Distinguish between static friction and rolling friction.
Subjective question
Static Friction
Rolling Friction
It acts between surfaces that are at rest relative to
each other.
It acts when an object rolls over another surface.
It prevents a stationary object from starting to move.
It opposes and slows down the rolling motion of an
object.
It is generally greater than rolling friction.
It is generally smaller than static friction.
Example: Trying to push a heavy stationary cupboard.
Example: The motion of a wheel or ball on the ground.
Wheels and ball bearings are used in machines because rolling
friction is smaller than sliding or static friction.
04
Write any three disadvantages of frictional force.
Subjective question
Three disadvantages of frictional force are:
Wear and tear: Friction damages machine
parts, shoes, tyres and other surfaces over time.
Production of unwanted heat: Friction
converts some useful energy into heat, which may damage
machines.
Loss of efficiency: Extra energy is required
to overcome friction, reducing the efficiency of machines.
05
Why is frictional force called a necessary evil?
Subjective question
Friction is useful because it allows us to walk, hold objects,
write on paper and stop vehicles by applying brakes.
However, friction also causes wear and tear, produces unwanted
heat and wastes energy.
Friction is called a necessary evil because we need it for many
daily activities, even though it also creates several problems.
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Exemplar Problems
Apply the concept of friction to real-life situations.
06
Give a real-life example to show that friction between two
surfaces increases when they are pressed harder.
Exemplar problem
Place a rubber eraser on a sheet of paper and move it gently.
It moves with relatively little resistance.
Now press the eraser harder against the paper and try to move
it again. It becomes more difficult to slide.
Pressing the surfaces harder increases the force between them,
which generally increases friction.
07
Suggest a way to prevent vehicles from skidding during rainy
days.
Exemplar problem
Vehicles should use tyres with proper grooves or deep tread
patterns.
The grooves help remove water from between the tyre and the
road. This improves the grip between the two surfaces and
reduces the chance of skidding.
Drivers should also reduce their speed and avoid sudden braking
on wet roads.
08
Does a raindrop falling towards the Earth experience any
frictional force?
Exemplar problem
Yes. A falling raindrop experiences air resistance, which is a
type of fluid friction.
As the raindrop moves through the air, it collides with air
particles. Air resistance acts in the direction opposite to
the motion of the raindrop and slows it down.
09
Choose one indoor sport and one outdoor sport. Explain the role
of friction in each sport.
Exemplar problem
Indoor sport – Table tennis:
Friction between the table-tennis ball and the rubber surface
of the bat helps a player control the speed, spin and direction
of the ball.
Outdoor sport – Football:
Friction between the studs of a player's shoes and the ground
provides grip. It helps the player run, turn and stop without
slipping.
10
What would happen if frictional forces disappeared completely?
Exemplar problem
Life would become extremely difficult if friction disappeared.
We would not be able to walk because our feet would keep
slipping.
Vehicles would not get enough grip to move, turn or stop.
Brakes would not work because braking depends on friction.
We would not be able to hold objects securely.
Writing with a pencil, pen or chalk would become impossible.
Nails, screws, knots and many machine parts would not remain
securely in place.
Friction is essential for movement, grip, writing, braking and
the working of many everyday objects.
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Excellent! You explored every answer.
Revise the key points once more before your examination.
Very helpful for Class 6 students! I liked how friction is explained using simple real life examples, especially walking, braking and sports. The question and answer format also makes revision much easier before exams.
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Very helpful for Class 6 students! I liked how friction is explained using simple real life examples, especially walking, braking and sports. The question and answer format also makes revision much easier before exams.
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