Class 9 Science - HARYANA
How Forces Affect Motion
The chapter 'How Forces Affect Motion' in Class 9 Science for the Haryana Board (BSEH) builds upon the foundational concepts of motion by introducing the causes behind it—forces. Students learn about balanced and unbalanced forces, inertia, and Isaac Newton's three laws of motion, which explain how objects behave at rest and in motion. A major focus is placed on the Conservation of Momentum, complete with numerical problems. This chapter is extremely crucial for board exams as it carries significant weightage, frequently featuring both conceptual reasoning questions based on everyday observations and numericals that test problem-solving skills.
Start Learning FreeKey Concepts
Balanced and Unbalanced Forces
Balanced forces are equal in magnitude and opposite in direction, resulting in zero net force and no change in motion. Unbalanced forces result in a net non-zero force that changes the speed or direction of an object's motion.
Newton's First Law of Motion and Inertia
An object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force. Inertia is the natural tendency of objects to resist a change in their state of motion.
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. It provides the quantitative definition of force through the famous equation F equals m times a.
Newton's Third Law of Motion
To every action, there is an equal and opposite reaction. These forces always act on two different bodies simultaneously and never cancel each other out.
Law of Conservation of Momentum
The total momentum of two objects before collision is equal to the total momentum after collision, provided there is no external unbalanced force acting on them.
Important Formulas
Board Exam Info
This chapter typically carries around 6 to 8 marks in the BSEH Class 9 Science examination. Common question types include numerical problems on momentum and force, conceptual reasoning questions based on daily life examples (like passengers falling forward when a bus stops suddenly), and direct statements or applications of Newton's laws of motion.
Frequently Asked Questions
Why do we fall forward when a moving bus suddenly applies brakes?
Due to inertia of motion, our upper body continues to remain in forward motion even when the bus and our feet stop suddenly.
What is the SI unit of momentum?
Kilogram meter per second (kg·m/s).
Do action and reaction forces cancel each other?
No, because action and reaction forces act on two different bodies, not on the same body.
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