View and Download the solved questions, solved numerical problems or 9th Class Physics notes of Chapter 4 “Turning Effect of Forces” of Punjab Textbook Board. These 9th class physics notes of 4th Chapter are according to the new syllabus (2013) of Punjab Boards including Lahore Board, Gujranwala Board, Sahiwal Board, Rawalpindi Board, Faisalabad Board, Multan Board, Bahawalpur Board, Federal Board, DG Khan Board and Sargodha Board. Students of 9th Class of all these board can facilitate from the physics notes given below. You can also download 9th Class Physics Chapter 4 Solved Questions and Numericals Problems.

### Unit 4: Turning Effect of Forces

By studying this chapter students will be able to: Define like and unlike parallel forces. State head to tail rule of vector addition of forces/vectors. Describe how a force is resolved into its perpendicular components. Determine the magnitude and direction of a force from its perpendicular components. Define moment of force or torque as moment = force x perpendicular distance from pivot to the line of action of force. Explain the turning effect of force by relating it to everyday life. State the principle of moments. Define the centre of mass and centre of gravity of a body. Define couple as a pair of forces tending to produce rotation. Prove that the couple has the same moments about all points. Define equilibrium and classify its types by quoting examples from everyday life. State the two conditions ‘ for equilibrium of a body. Solve problems on simple balance systems when bodies are supported by one pivot only. Describe the states of equilibrium and classify them with common examples. Explain effect of position of the centre of mass on the stability of simple objects.