Equilibrium Of Forces


Welcome to the comprehensive course material on the topic of Equilibrium of Forces in Physics. This topic delves into the intricate balance of forces acting on objects, ensuring they remain at rest or move with a constant velocity.

One of the fundamental objectives of this course is to equip you with the ability to apply the conditions for the equilibrium of coplanar forces to tackle various problem-solving scenarios. Understanding how forces interact and cancel each other out within the same plane is crucial in determining stability.

Furthermore, we will explore the triangle and polygon laws of forces, which provide valuable insights into how multiple forces interact simultaneously. By utilizing these laws, you will learn how to analyze and solve equilibrium problems efficiently.

Another essential aspect we will cover is Lami’s Theorem, a powerful tool that aids in understanding the equilibrium of forces acting on an object. This theorem will enhance your problem-solving skills and enable you to tackle complex scenarios with ease.

Delving deeper into the topic, we will delve into moment of a force and couple, shedding light on how these concepts influence the equilibrium of objects. By grasping the significance of moments, you will be able to analyze forces' rotational effects more effectively.

Moreover, we will discuss applications of moment of a force and couple, illustrating real-world examples where these principles play a crucial role. Understanding these applications will broaden your understanding and highlight the practical significance of equilibrium in various scenarios.

Additionally, we will explore the conditions for the equilibrium of rigid bodies when subjected to both parallel and non-parallel forces. This section will provide you with the necessary tools to analyze and solve equilibrium problems involving complex force systems.

By mastering resolution and composition of forces in two perpendicular directions, you will develop a solid foundation in analyzing forces' components. This skill is vital in determining the resultant and equilibrant forces acting on an object.

Finally, we will delve into the concept of centre of gravity and stability, distinguishing between stable, unstable, and neutral equilibria. Understanding these equilibrium states will enrich your knowledge of how objects maintain balance under varying conditions.


  1. Determine The Resultant And Equilibrant Of Forces
  2. Differentiate Between Stable, Unstable And Neutral Equilibra
  3. Use Triangle And Polygon Laws Of Forces To Solve Equilibrium Problems
  4. Use Lami’s Theorem To Solve Problems
  5. Resolve Forces Into Two Perpendicular Directions
  6. Determine Moment Of A Force And Couple
  7. Describe Some Applications Of Moment Of A Force And Couple
  8. Apply The Conditions For The Equilibrium Of Coplanar Forces To Solve Problems
  9. Apply The Conditions For The Equilibrium Of Rigid Bodies To Solve Problems

Lesson Note

In Physics, the concept of equilibrium of forces is fundamental in understanding how different forces acting on an object interact to produce either a state of rest or uniform motion. Equilibrium can be classified into two categories: static equilibrium, where the object remains at rest, and dynamic equilibrium, where the object moves with uniform velocity. This topic is crucial for solving a variety of real-world problems, from engineering structures to everyday items.

Lesson Evaluation

Congratulations on completing the lesson on Equilibrium Of Forces. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

  1. A block is in equilibrium under the action of three forces as shown in the diagram. What is the magnitude of F3? A. F1 B. F2 C. F1 + F2 D. F1 - F2 Answer: B. F2
  2. Which of the following is NOT a condition for equilibrium of coplanar forces? A. Net force is zero B. Net torque is zero C. Sum of all vertical forces is zero D. Sum of all horizontal forces is zero Answer: B. Net torque is zero
  3. In the equilibrium of coplanar forces, what is the likely result if forces are not in the same plane? A. Stable equilibrium B. Unstable equilibrium C. Neutral equilibrium D. No equilibrium can be achieved Answer: D. No equilibrium can be achieved
  4. Forces acting on an object are in equilibrium when: A. Only the magnitude of forces are equal B. Only the directions of forces are equal C. Both the magnitudes and directions of forces are equal D. Forces are not equal in any aspect Answer: C. Both the magnitudes and directions of forces are equal
  5. According to Lami's theorem, what is the relationship between three concurrent forces in equilibrium? A. They are proportional to each other B. They form a right angle triangle C. They are inversely proportional to each other D. Their internal angles are equal Answer: A. They are proportional to each other
  6. The turning effect of a force about an axis is known as its: A. Torque B. Momentum C. Acceleration D. Velocity Answer: A. Torque
  7. A couple is formed by two forces that are: A. Parallel, same magnitude, opposite direction B. Parallel, same direction, same magnitude C. Parallel, opposite direction, unequal magnitude D. Non-parallel, same magnitude, opposite direction Answer: A. Parallel, same magnitude, opposite direction
  8. When a body is in neutral equilibrium, it tends to: A. Return to its original position B. Remain in its new position C. Move away from its original position D. Oscillate between positions Answer: D. Oscillate between positions
  9. What is the center of gravity of an object? A. The point where weight is zero B. The point where net force is maximum C. The point where all forces are in equilibrium D. The point where entire weight can be considered to act Answer: D. The point where entire weight can be considered to act

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Past Questions

Wondering what past questions for this topic looks like? Here are a number of questions about Equilibrium Of Forces from previous years

Question 1 Report

The basic principle of operation of a beam balance is------------------

Question 1 Report

Which of the following liquids has the highest surface tension?

Question 1 Report

Two forces forming a couple are separated by a distance of 25cm. If one of the forces equals 40N, what is the moment of the couple?

Practice a number of Equilibrium Of Forces past questions