9th Class Physics Chapter 4 Notes

Complete Notes of 9th Class Physics Chapter 4 Notes Turning Effect of Forces notes of 9th Class Physics English Medium written by Professor Tayyab Shahzad. These computerized notes are very helpful in the preparation of Turning Effect of Forces Notes for students of the 9th Class Physics Chapter 4 Notes these are according to the paper patterns of all Punjab boards.

• Here are the detailed Class 9 Physics Notes Chapter 4 to help you prepare for your exams.
• Turning Effect of Forces Exercise Multiple Choice Questions ( MCQs ) with correct Answers
• Turning Effect of Forces Exercise Short Questions with Answers
• Define the following: (a) Resultant vector (b) Torque (c) Centre of mass (d) Centre of gravity
• How head to head-to-tail rule helps to find the resultant forces?
• When a body is said to be in equilibrium?
• How can a force be resolved into its rectangular components?
• Differentiate the following: (a) Like and unlike parallel forces. (b) Torque and couple. (c) Stable and neutral equilibrium.
• What is the second condition for equilibrium?
• Why there is a need for the second condition for equilibrium if a body satisfies the first condition for equilibrium?
• You can also download the Class 9 Physics Chapter 4 Notes pdf for free.
• Give an example of a moving body that is in equilibrium.
• Why a body cannot be in equilibrium due to a single force acting on it?
• Think of a body which is at rest but not in equilibrium.
• Why the height of vehicles is kept as low as possible?
• Explain what is meant by stable, unstable, and neutral equilibrium. Give one example in each case.
• Important Conversion and Important Formulas
• Turning Effect of Forces Exercise Numericals with Solutions
• AXIS OF ROTATION: Consider a rigid body rotating about a line. The particles of the body move in circles with their centres all lying on this line. This line is called the axis of rotation of the body. Forces that produce turning effect are very common. Turning pencil in a sharpener, turning stopcock of a water tap, turning doorknob and so on are some of the examples where a force produces turning effect. 
• If you're looking for comprehensive Physics Notes for Class 9th Chapter 4, you've come to the right place.
• "The turning effect of a force is called torque or moment of the force".
• LINE OF ACTION OF A FORCE: The line along which a force acts is called the line of action of the force. line BC is the line of action of force F.
• MOMENT ARM: The perpendicular distance between the axis of rotation and the line of action of the force is called the moment arm of the force. It is represented by the distance L.
• Principle of moments class 9: "A body is balanced if the sum of clockwise moments acting on the body is equal to the sum of anticlockwise moments acting on it".
• CENTRE OF MASS: It is observed that the centre of mass of a system moves as if its entire mass is confined at that point. A force applied at such a point in the body does not produce any torque in it i.e. the body moves in the direction of net force F without rotation.
• "Centre of mass of a system is such a point where an applied force causes the system to move without rotation".
• CENTRE OF GRAVITY: A body is made up of a large number of particles as illustrated. Earth attracts each of these particles vertically downward towards its centre. The pull of the Earth acting on a particle is equal to its weight. These forces acting on the particles of a body are almost parallel. The resultant of all these parallel forces is a single force equal to the weight of the body. A point where this resultant force acts vertically towards the centre of the Earth is called the centre of gravity G of the body.
• "A point where the whole weight of the body appears to act vertically downward is called centre of gravity of a body".