# FBISE 9th Class Physics Chapter 4 Turning Effect Short Questions Answers

FBISE 9th class Physics Chapter 4 Turning Effect Short Questions with answers are combined for all 9th class(Matric/ssc) Level students. Here You can prepare all Physics Chapter 4 Turning Effect short question in unique way and also attempt quiz related to this chapter. Just Click on Short Question and below Answer automatically shown. After each question you can give like/dislike to tell other students how its useful for each.

Class/Subject: 9th Class Physics

Chapter Name: Turning Effect

Board: Federal  Board

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## FBISE 9th Class Physics Chapter 4 Turning Effect Short Questions Answers

Define Resultant Vector

Ans. A resultant vector is a single vector that has the same effect as the combined effect of all the vectors to be added.

Define Torque?

Ans. The turning effect of a force is called torque or moment of the force.

Define Centre of mass?

Ans. The Centre of the mass of a system is such a point where an applied force causes the system to move without rotation.

Define Centre of Gravity?

Ans. A point where the whole weight of the body appears to act vertically downwards is called the Centre of gravity of a body.

What is meant by parallel forces?

Ans. In a plane, if several parallel forces act on a body such that points of action are different but lines of action are parallel to each other, then these forces are called parallel forces.

What are parallel forces?

Ans. Like parallel forces are those forces that are parallel to each other and have the same direction.

What is unlike parallel forces?

Ans. Unlike parallel forces are those forces are parallel but have a direction opposite to each other.

Ans. According to this rule, vectors are drawn in such a way that the head of the first vector is joined with the tail of the second vector.

What is resultant force?

Ans. A resultant force is a single force that has the same effect as the combined effect of all the forces to be added. And resultant vector is drawn in such a way that the tail of the first vector is joined with the leaders of the last vector.

Define Couple?

Ans. A couple is formed by two unlike parallel forces of the same magnitude but not along the same line.

Define Equilibrium?

Ans. If no force is acting on the body or several forces act on a body in such a way that their resultant is zero, then if the body is at rest will remain at rest and if the body is in motion, it will continue moving with a uniform velocity. This condition of the body is called equilibrium.

Define unstable equilibrium?

Ans. If a body does not return to its previous position where sets after the slightest tilt are said to be in unstable equilibrium.

Define neutral equilibrium?

Ans. If a body remains in its new position when disturbed from its previous position, it is said to be in a state of neutral equilibrium.

What is the rigid body?

Ans. A body is composed of a large number of particles. If the distance between all these pairs of particles of the body does not change by applying a force then it is called a rigid body.

Define axis of rotation?

Ans. During rotation, the particles of the rigid body move in circles with their centers all lying on a line. This straight line is called the axis of rotation of the body.

What is meant by the principle of moments?

Ans. In a balanced body, if the sum of clockwise moments acting on the body is equal to the sum of anti-clockwise moments acting on it.

What do you mean by a line of action of a force?

Ans. The line along which a force act is called the line of action of the force.

Define moment arm?

Ans. The perpendicular distance between the axis rotation and the line of action of the force is called the moment arm of the force. It is represented by the distance L.

What do you mean by newton-meter (Nm)?

Ans. A torque of 1 Nm is caused by a force of 1N acting perpendicular to the moment arm 1m long.

What is trigonometry?

Ans. Trigonometry is that branch of mathematics that deals with the properties of a right-angled triangle.

Define Terminal Velocity?

Ans. The maximum and constant velocity of an object falling vertically downwards is called terminal velocity.

Can the nut of the axle of a bike be loosened with a hand why we use a spanner for this purpose?

Ans. No, we cannot loosen the nut of the axel of a bike. Normally we use a spanner because a spanner increases the turning effect of the force which easily loosened the nut of the axel of a bike.

Why it is easy to open and close the door by pulling it as it handles?

Ans. We open or close a door by pushing or pulling it. Here push or pull turn the door about its hinge or axis of rotation. The door is opened or closed due to the turning effect of the force acting on it.

On what factors rotation produce in a body depend?

Ans. i. The magnitude of the force
ii. The perpendicular distance between the line of action of the force and the axis of rotation.

How can we increase torque by keeping the force constant?

Ans. We can increase the torque by increasing the perpendicular distance from the line of action of force to the point of rotation that is moment arm by keeping the force constant, according to the relation
τ = r x F

Can a body move in equilibrium? Explain.

Ans. Yes, if a body is moving with uniform velocity then the body is in equilibrium because neither linear nor rotational acceleration is produced in the body.

Will a body be in equilibrium under the action of a single force?

Ans. No, the body will not be in equilibrium because the first condition of equilibrium will not be fulfilled. Since a single force can never be zero and linear acceleration will be produced. Therefore we can say that a body cannot be equilibrium under the action of a single force.

Can a body be in equilibrium if it is revolving clockwise under the action of a single force?

Ans. No, the body will not be in equilibrium because the second condition of the equilibrium will not be fulfilled. Since single torque can never be zero and rotational acceleration will be produced. Therefore we can say that a body cannot be equilibrium under the action of a single torque.

Give an example of a case when the resultant force is zero but resultant torque is not zero.

Ans. In the case of a couple, two equal and opposite forces are acting on the same body but even then the body rotates. In this case, the resultant force is zero but the resultant torque is not zero. E.g. while turning a car, the forces applied on the steering wheel by hands produce rotation in the steering wheel.

How do we know whether a body is in a stable or unstable equilibrium due to the position of its center of gravity?

Ans. If after disturbance, the center of gravity of the body is raised as compared to the initial position then the body will be in the state of stable equilibrium and if after disturbance, the center of gravity of the body is lowered down as compared to the initial position then the body will be in the state of unstable equilibrium.

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