TS 8th Class Physical Science Important Questions 1st Lesson Force

These TS 8th Class Physical Science Important Questions 1st Lesson Force will help the students to improve their time and approach.

TS 8th Class Physical Science Important Questions 1st Lesson Force

Question 1.
Would it be possible to ride a car if there were no friction between the tires of car and the road?
Answer:
If there is no friction between car tyres and road we can not drive car. Car will skid on the road. We can not control the velocity, direction of the car.

Question 2.
What is normal force?
Answer:
The force that a solid surface exerts on any object in the normal direction is called the normal force.

Question 3.
What is tension?
Answer:
Tension is feeling of tightness in a rope or a string.

Question 4.
Tension:
As shown in the figure a stone is suspended with the help of a string and its free end is tied to the ceiling
a) What is the state of the stone?
Answer:
The stone is at rest.

b) What forces are acting on It?
Answer:
Two forces acting on it.

• Gravitational force (Downward direction)
• Tension in the string (Upward direction)

c) What will happen if the string is broken?
Answer:
If string is broken, the stone move downward direction due to the gravitational force.

Question 5.
What is gravitational force?
Answer:
The force of attraction between any two masses or two bodies everywhere in the universe is called gravitational force.

Question 6.
Why do stone thrown up into the sky come back and falls on the earth?
Answer:
Any object which is thrown up into the sky will fall on the earth due to earth’s gravitational force. So stone will come back and falls on the earth due to gravitational force.

Question 7.
Imagine that the object is kept in a lift which is accelerating. Is the net force acting on the object Is zero? Why?
Answer:
The net force acting on the object which is in the accelerating lift is non-zero. Because the objects are in non-uniform motion, it is said to be in acceleration.

Question 8.
What is a free-body diagram?
Answer:
The diagram showing all the relevant forces acting on a body at a particular time is called free-body diagram. It is indicated by FBD.

Question 9.
What do forces do?
Answer:

1. Force can change the shape of an object.
2. Force can move an object from the position of rest.
3. Force can change the speed of motion.
4. Force can change the direction of motion.

Question 10.
An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms: muscular, contact, non-contact, gravity, friction, shape, attraction.
a. To stretch the bow, the archer applies a force that causes a change in its …………….
b. The force applied by the archer to stretch the bow is an example of ………….. force.
c. The type of force responsible for a change in the state of motion of the arrow is an example of a ………….. force.
d. While the arrow moves towards its target, the forces acting on it are due to …………
and that due to ………………. of air.
Answer:
a) shape
b) muscular (contact)
c) contact
d) gravitational, friction

Question 11.
Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change ¡n its state of motion.
Answer:
Force due to gravity does not bring a change in its state of motion because equal amount of force is being applied vertically upward. One can observe the effect of the force acting on the bucket or on our body is the form of falling of the object towards the earth when the force applied on any object above the ground to lift it is withdrawn.

Question 12.
What do you know by the state of motion?
Answer:
The state of motion of an object is described by its speed and the direction of motion, The state of rest is considered to be the state of zero speed. An object may be at rest or in motion; both are its state of motion. Any change in the speed. or direction of motion, or both, implies a change in the state of motion of the object.

Question 13.
On what factors does the effect of force depend?
Answer:
The effect of a force depends on two things.

1. The amount of force applied. The more the force is applied the greater the effect will be.
2. The area on which the force is applied. The smaller the area the force is applied on, the greater the effect will be.

Question 14.
Have you ever seen a game of tug-of-war? In this game, two teams pull at a rope in opposite direction. All members of either team try to pull the rope in their direction. Sometimes the rope simply does not move. Explain why.
Answer:
We know that if two forces act in opposite directions on an object, the net force acting on it is the difference between the two forces. If the two teams pull the rope with equal force, the forces will be in opposite directions and will cancel each other and the rope will not move. The net force acting on the rope is zero.

Question 15.
We know that a force applied on an object causes either a change in its state of motion or its shape. Different types of events are listed in the following table. Tell the type of effect in each case.
Answer:

Question 16.
State an example for a situation mentioned below ¡n which a force:
a) Changes the speed of an object
b) Changes the shape of an object
c) Changes the direction of an object.
Answer:
a. Kick a football which is in rest. The ball moves with some speed. So the force acting on the ball changes the speed of it.
b. If you hold a sponge duster in your hand, and press it by some force, the shape of the duster changes. Here force changes the shape of an object.
c. If we apply force on carrom coin with the striker, in some case coin moves in another direction. Striker also changes its direction after hitting the coin.

Question 17.
Detect the errors ¡n the following statement and rewrite it in making necessary corrections.
“Because the car Is at rest, no forces are acting on it”.
Answer:
The correct statement is” Some forces are acting on it even though the car is at rest”.

Question 18.
Objects change their state of motion due to the net force acting on them. Discuss.
Answer:

1. To start the game, football is kept in the center of the ground. It is at rest.
2. The ball is kicked and it moves.
3. Here kicking the ball means applying force on it. So force changes the state of rest into motion.
4. In the same way we can stop the moving ball and bring back to rest by catching it.

Question 19.
When you push a heavy object, It doesn’t move. Explain the reason in terms of net force.
Answer:

1. Push a heavy box which is kept on a floor with some force to move horizontally.
2. But the box does not move, because there is a frictional force which is equal and opposite to the applied force on the box.
3. Here the net force acting on the box is equal to zero.
   Applied force (F) = – Frictional Force (F_r)
   Net force = F + (F_r) = 0
4. From this, we conclude that if net force acting on a body which is at rest is equal to zero, then the body doesn’t move. It remains in rest position.

Question 20.
a) Take two identical straws and suspend one piece freely. Rub the other straw with a piece of paper. Bring the rubbed end of the straw near the suspended one. What do you observe from this activity? Can you tell which type of force It is?
b) Comb your dry hair. Bring the comb to the small pieces of paper. What do you observe? Explain.
Answer:
a) The rubbed straw attracts the suspended one when it brings near to it. Because when we rub the straw with a paper it acquires some charge. Here the force exerted by a charged body (rubbed straw) on another uncharged body is known as electrostatic force. it is a force at a distance (non-contact force).
b) When we comb our dry hair, comb acquires an electrostatic charge on its surface. When it is brought near to pieces of paper, the pieces acquire opposite charge and will be attracted by the comb. This is also an electrostatic force and a non-contact force.

Question 21.
A stick is placed on steps as shown in figure. Draw normal forces on the stick.

Answer:

Question 22.
Observe the figure below and find in which direction does the force of friction act? And also find where would you find the normal forces and in which direction?
Answer:
Friction force (f) acts opposite direction to the direction of motion, in between table and ground. Normal force (N) acts in upward direction.

Question 23.
A monkey hangs stationary at the end of the vertical vine. What forces act on the monkey?
Answer:
Two forces acting on a monkey. They are
1. Gravitation force acting in downward direction.
2. Tension in the string acting vertically upward direction.

Diagrams:

1.

2.

3.

4.

5.

6.

7.

Multiple choice questions
Question 1.
Pressure is …………. .( )
A) volume/area
B) force/area
C) mass/ area
D) density/ area
Answer:
B) force/area

Question 2.
Force is a ……………….. . ( )
A) power
B) pressure
C) push or pull
D) friction
Answer:
C) push or pull

Question 3.
Force can be measured by ( )
A) magnitude
B) mass
C) volume
D) weight
Answer:
A) magnitude

Question 4.
Force acting on a surface in a direction perpendicular to it is known as ……………. .( )
A) thrust
B) force
C) pressure
D) density
Answer:
A) thrust

Question 5.
The pressure exerted by the atmospheric air is known a …………….. . ( )
A) atmospheric pressure
B) biosphere
C) troposphere
D) all of the above
Answer:
A) atmospheric pressure

Question 6.
Force can affect the state of motion of a body by changing ( )
A) direction of speed
B) speed
C) state of motion
D) all
Answer:
D) all

Question 7.
Which is not a non-contact force? ( )
A) electrostatic
B) magnetic
C) gravity
D) muscular
Answer:
D) muscular

Question 8.
A spring balance Is used for measuring ( )
A) mass
B) weight
C) pressure
D) speed
Answer:
B) weight

Question 9.
The force exerted by one object on another by virtue of their masses ……………….. .( )
A) magnetic force
B) electrostatic force
C) gravitational
D) frictional
Answer:
C) gravitational

Question 10.
1-kilogram weight is ………………… . ( )
A) 98 N
B) 9.8 N
C) 0.98 N
D) 0.098 N
Answer:
B) 9.8 N

Question 11.
The standard unit of force is …………………… . ( )
A) m/s
B) m/s²
C) gr / N
D) Newton
Answer:
D) Newton

Question 12.
Which of the following is a contact force? ( )
A) friction
B) magnetic
C) gravity
D) electrostatic
Answer:
A) friction

Question 13.
Which of the following is non-contact force? ( )
A) magnetic
B) gravity
C) electrostatic
D) all the above
Answer:
D) all the above

IIT Foundation Material

Consider a gymnast hanging from the rings.
Question 1.
If the girl shown in figure hangs with her weight evenly divided between the two rings, how would scale readings in both supporting ropes compare with her weight?
Answer:
The reading on each scale will be half her weight. The sum on the readings on both scales then equals her weight.

Question 2.
Suppose the girl hangs with slightly more of her weight supported by the left ring. How would a scale on the right read?
Answer:
When more of her weight is supported by the left ring, the reading on the right is less than half her weight, The sum of the scale readings equals her weight, no matter how she hangs. If one scale reads two. thirds her weight, the other scale will also read one-third her weight.

Question 3.
Suppose you stand on two bathroom scales with your weight evenly distributed between the two scales. What is the reading on each of the scales? What happens when you stand with more of your weight on one foot than the other?
Answer:
The reading on each scale is half our weight. because the sum of the scale readings must balance our weight. So the net force on us will be zero. If we lean more on one scale than the other, more than half our weight will be read on that scale but less on the other. So the’ will still add up to our weight.

Question 4.
Two parachutists are there one a hea person and one a light person. They jump from the same altitude with parachutes of the same site.
1. Which person reaches the terminal speed first?
2. Which person has the higher terminal speed?
3. Which person reaches the ground first?
4. II there were no air resistance, like on the moon, how would your answers to these questions differ?
Answer:
Let us think of a coin and a feather falling in air.

1. The lighter person reaches terminal speed first just as a feather reaches terminal speed very quickly.
2. The heavy person falls faster and reaches a higher terminal speed just as a coin falls faster than a feather through air.
3. Just as a coin falls first and a feather later, the heavier person falls faster and will reach the ground first.
4. If there were no air resistance, there would be no terminal speed at all. Both would be in free fall, and both would hit the ground at the same time.