Class 9 Science - BIHAR
How Forces Affect Motion
The chapter 'How Forces Affect Motion' in Class 9 Science builds the foundation of classical mechanics as per the Bihar (BSEB) curriculum. It explores Newton's Laws of Motion, the concept of inertia, and the relationship between mass, force, and acceleration. Students also learn about momentum and the law of conservation of momentum. This chapter is vital for board exams as it carries high weightage and forms the base for numerical problems and conceptual questions in physics that frequently appear in the BSEB Class 9 and annual examinations.
Start Learning FreeKey Concepts
Balanced and Unbalanced Forces
Balanced forces do not change the state of motion of an object, whereas unbalanced forces act on an object to change its speed or direction of motion.
Newton's First Law of Motion and Inertia
An object remains in a state of rest or uniform motion in a straight line unless compelled by an external force to change that state. Inertia is the natural tendency of objects to resist a change in their state of motion.
Momentum
Momentum is the product of an object's mass and its velocity, representing the power of motion contained in the body.
Newton's Second Law of Motion
The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force.
Newton's Third Law of Motion
To every action, there is an equal and opposite reaction, and they act on two different bodies.
Law of Conservation of Momentum
The total momentum of two objects before collision is equal to the total momentum after collision, provided no external unbalanced force acts on them.
Important Formulas
Board Exam Info
In the Bihar (BSEB) Class 9 science examination, this chapter typically carries around 6 to 8 marks. Questions usually include a mix of objective (MCQs), short-answer conceptual questions based on inertia or Newton's laws, and simple numerical problems based on force and momentum.
Frequently Asked Questions
Why do we fall forward when a moving bus suddenly stops?
Due to inertia of motion, our lower body stops with the bus, but our upper body continues to move forward until an external force acts on it.
What is the SI unit of force and momentum?
The SI unit of force is Newton (N) and the SI unit of momentum is kilogram meter per second (kg·m/s).
Do action and reaction forces cancel each other out?
No, action and reaction forces do not cancel each other because they act on two different bodies, not on the same body.
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