Class 9th · Physics · Chapter 4
Chapter 4: Turning Effects of Force
Chapter 4 of the Punjab Board Class 9th Physics textbook runs from page 80 to 104 and covers 10 topics. Its exercise has multiple choice questions, short / constructed response questions, comprehensive questions and numerical problems. Open any of those pages in GenZ Books, tap a question, and the answer is worked from this chapter.
Open Chapter 4 of Physics in GenZ Books
The same Class 9th textbook, page for page. Tap any question and get the answer worked from that chapter — English and Urdu.
Topics in this chapter
- 4.1Like and Unlike Parallel Forcesp. 81
- 4.2Addition of Forcesp. 81
- 4.3Turning Effect of a Forcep. 82
- 4.4Resolution of Vectorsp. 84
- 4.7Centre of Gravity and Centre of Massp. 88
- 4.8Equilibriump. 90
- 4.10States of Equilibriump. 94
- 4.11Improvement of Stabilityp. 95
- 4.12Application of Stability in Real Lifep. 96
- 4.13Centripetal Forcep. 98
Exercise
- Multiple Choice Questionsp. 101
- Short / Constructed Response Questionsp. 102
- Comprehensive Questionsp. 103
- Numerical Problemsp. 103
GenZ Books has 90 questions from this chapter catalogued, each answered from the pages above.
A sample answer from GenZ Books
Explain · page 81: 4.1 Like and Unlike Parallel Forces If the parallel forces are acting in the same direction, then they are called like parallel forces and if their directions are opposite to one another, they are called unlike parallel forces. Three forces F,, F, and F, are shown in Fig. 4.1 acting on a rigid body at different points. Here, the forces F, and F, are like parallel forces but F, and F, are unlike parallel forces.
Core idea When two or more forces act along the same straight line, we look at the direction they point. If they point the same way they are like parallel forces; if they point opposite ways they are unlike parallel forces.
What to remember
- Parallel forces – forces whose lines of action are parallel (متوازی قوتیں).
- Like parallel forces – all act in the same direction (e.g., $F_1$ and $F_2$ both to the right).
- Unlike parallel forces – act in opposite directions (e.g., $F_2$ to the right, $F_3$ to the left).
- The forces may be applied at different points on the rigid body, but the direction rule still decides “like” or “unlike”.
Everyday example (Pakistan) When a rickshaw is being pulled forward by the driver’s hand on the handle ($F_{\text{hand}}$) and at the same time the wind pushes it backward ($F_{\text{wind}}$), the two forces are unlike parallel forces because they act along the same line (the rickshaw’s length) but in opposite directions. If two people push a cart from behind in the same direction, their pushes are like parallel forces.
Common mistake Students often think that only forces applied at the same point can be compared as “like” or “unlike”. The rule depends only on the direction of the forces, not on where they act.
Deeper idea (optional) Both kinds of parallel forces can be combined vectorially to give a single resultant force that determines the motion of the body.
In short: Like parallel forces point the same way; unlike parallel forces point opposite ways, regardless of where they act on the body.
AI-generated from the chapter text by GenZ Books. It can make mistakes — check it against your textbook and your teacher.