Physics Ninja: Torque and Equilibrium of Rigid Bodies

Name: Physics Ninja: Torque and Equilibrium of Rigid Bodies
Rating: 4.8 (47 reviews)

Comprehensive course covering the topics of torque, equilibrium and center of mass and stability.

Created byEric Meloche, Ph.D.

Last updated 6/2025

English

What you'll learn

How to calculate torque, center of mass, and solve equilibrium problems

Course content

6 sections • 52 lectures • 5h 5m total length

Introduction1:00

Introduction: Force vs Torque3:46
Torque Definition: F and r are perpendicular2:43
Torque: Magnitude and Direction6:04
Calculating the Net Torque5:17
General Definition of Torque: Part 13:11
Define torque for rigid bodies using RF sin theta, the shortest distance to the line of action, and the perpendicular component of the force.
General Definition of Torque: Part 21:34
Explore torque behavior: zero torque for angles 0 or 180 degrees, maximum torque for 90 or 270 degrees; equal magnitudes arise with equal forces, emphasizing the angle theta.
Understanding Sin(theta)2:31
Example Problem: Comparing Torques6:37
Example Problem: Swinging Door4:47

Introduction: Center of Mass2:37
Explore the center of mass and how torque determines equilibrium, using a baseball bat and pivot examples to demonstrate balancing and calculating center of mass in varied shapes.
Where is the Center of Mass?2:10
Determine the center of mass for symmetric shapes on planes of symmetry under constant density to assess balance. Note it may lie inside or outside the object.
Center of Mass for 2 particles3:26
Example: Calculate the position of the center of mass3:49
Example 2: Center of mass of sphere and rod system4:04
Center of Mass in 2 and 3 Dimensions2:44
Example: Masses on an Equilateral Triangle5:27
Calculate the center of mass for three masses 1.2, 2.5, and 3.4 kg at the vertices of an equal lateral triangle, edge 140 cm, using a two-dimensional coordinate system.
Example Problem: Rectangular Metal Frame8:48

Introduction to Static Equilibrium3:02
Explore static equilibrium by applying free body diagrams to ensure net force and net torque equal zero, using center of mass, weight, and normal force to analyze pivots.
Examples of Static Equilibrium1:54
Delve into static equilibrium by balancing forces and torques to keep objects at rest and not rotating, with examples like a book, a hanging sign, and a ladder.
Example: Concept Check3:06
Analyze a light rod with equal opposite forces to confirm force equilibrium but not torque equilibrium, illustrating how net torque depends on pivot placement.
Example Problem: Seesaw Father and Daughter6:24
Choice of pivot point2:14
Center of Gravity3:25
Compute torque on a beam by using the center of gravity (center of mass) or by summing small-mass torques; torque equals total mass times g times distance to the pivot.
Center of Gravity (cont)3:05
Example: Torque on a Ladder due to Gravity4:05
Problem Solving Strategy3:31
Draw sketches and free body diagrams, place forces at their points of application, resolve into components in a convenient coordinate system, and apply torque and equilibrium equations.
Which Free Body Diagram is Correct?3:48
Example Problem: Ladder Against a Wall0:57
Example Problem Solution: Ladder Against a Wall9:28
Example: Student Center of Mass Problem3:29
Example Problem: Tension in the Spring Scale4:43
Illustrates torque and equilibrium for a horizontal rigid bar weighing 100 N, hinged at the wall and held by a ceiling spring scale at 30 degrees, finding tension.
Example: Three Spoke Wheel4:09
Example: Horizontal Beam Problem10:49

Problem 1: Finding the net torque3:33
Problem 2: Comparing torques2:49
Problem 3: Center of Mass of Rectangle with Missing Piece18:39
Problem 4: Torque and the square6:05
Problem 5a: Finding Tension and Reaction Forces10:57
Problem 5b: Finding Tension and Reaction Forces11:39
Problem 6: Physics Ninja Walking on a Beam20:05
Problem 7: Reaction Forces of Beam against a Wall8:40
Problem 8: Claw Hammer Pulling a Nail5:04
Problem 9: Pulling a Wheel Onto a Curb12:37
Problem 10: The Book Stacking Problem19:27
Problem 11: Forces Acting on 2 Marbles in a Jar16:07
Problem 12: Designing of a Decorative Mobile7:58
Problem 13: Center of Mass of a Square Plate with a Cut Out12:39
Treat the square with a circular cutout as two masses using the negative-mass method to compute center of mass and show the shift toward the top diagonal of 0.061 a.

Requirements

Basic understanding of Forces, Vectors, and Newton's Laws

Description

This course covers torque, center of mass, rigid bodies in equilibrium, and the stability of objects. The course is a mix of lectures and problem solving tutorials. Students will learn to how to calculate torque, how to evaluate the center of mass of systems of particles and objects with uniform density. I will teach you how to approach problems and help you develop your own problem solving strategies to become a better problem solver.

Part 1: Torque

What is torque?
Understand how torque is different from forces
Calculate torque using 3 different techniques (standard methods, force components, and moment arms)
Several example problems to practice

Part 2: Center of Mass

Learn how to find the center of mass of symmetric objects
Calculating the center of mass of systems of particles in 1D, 2D, and 3D.
Practice problems

Part 3: Static Equilibrium

Conditions for Static Equilibrium
Problem solving strategies
Picking the right pivot location
Several example problems to practice the problem solving techniques.

Part 4: Various Problem Section

Practice solving Torque and center of mass problems and compare your answers to those of Physics Ninja
Section contains conceptual questions and algebraic questions ranging from easy to very challenging.

If at any point you don't understand something in my videos please feel free to reach out. I'm always willing to help someone learn. Physics Ninja always has your back!

Happy Learning

Dr. E., Physics Ninja and Expert Physics and Math Teacher.

Who this course is for:

AP physics students, first year undergraduate physics, MCAT physics prep and anyone
Students studying for physics exams

Physics Ninja: Torque and Equilibrium of Rigid Bodies

What you'll learn

Explore related topics

Course content

Introduction1 lecture • 1min

Torque9 lectures • 37min

Center of Mass8 lectures • 33min

Static Equilibrium16 lectures • 1hr 8min

Stability4 lectures • 11min

Problems and Solutions14 lectures • 2hr 36min

Requirements

Description

Who this course is for: