Unseen passage for Class 9 - Passage 10

Unseen passage - A chemical reaction involves the rearrangement or alteration of the molecular structure of a substance. Such reactions occur in various everyday situations, including food digestion, photosynthesis, metal rusting, wood burning, and battery functioning.

The speed at which a chemical reaction occurs can vary widely, ranging from rapid explosions to slow processes like metal rusting. The duration required for a chemical reaction to reach completion is referred to as its reaction rate.

Several types of chemical reactions exist. A synthesis reaction combines two substances to create a new compound. The substances being combined, known as reactants, may be individual elements or compounds. The result, or product, of a synthesis reaction is always a compound, and it can be represented by the equation A + B = AB. Conversely, a decomposition reaction involves the breakdown of a complex substance into simpler substances and is expressed by the equation AB → A + B.

In a combustion reaction, oxygen reacts with another compound to produce water and carbon dioxide, releasing energy in the form of heat and often light or flame. Combustion reactions, commonly known as burning, play a significant role in various processes.

A displacement reaction occurs when one compound takes a substance from another. In a single displacement reaction, a more reactive element replaces a less reactive one, and it is represented by the equation A + BC → AC + B. In a double displacement reaction, compounds on the left side of the equation exchange substances, as seen in the form AB + CD → AD + CB. Double displacement reactions typically involve interactions between a metal and a nonmetal or between acids and bases.

Unseen passage - Isaac Newton, a seventeenth-century scientist, provided explanations for the motion of objects in the physical universe. These explanations, known as Newton's Laws of Motion, universally apply to all objects on Earth, regardless of the time or circumstances.

Newton's laws revolve around key concepts, starting with force, which can push or pull an object, causing it to move, stop, accelerate, decelerate, or change its shape. Forces, present everywhere, act on all objects. Gravity, a pervasive force on Earth, pulls objects toward its center, keeping them grounded.

Direction determines how an object moves when subjected to force, while strength indicates the force's exertion. Greater force strength results in more significant object displacement. Acceleration, involving a change in velocity (speed and direction), leads to an object speeding up when both acceleration and velocity align, and slowing down when they oppose each other.

Newton's First Law of Motion, known as the Law of Inertia, asserts that objects at rest tend to stay at rest, and objects in motion tend to remain in motion due to resistance to a change in motion.

Newton's Second Law of Motion states that the greater an object's mass, the more force is required to accelerate it.

Newton’s Third Law of Motion posits that for every force acting on an object (action), there is an equal and opposite reaction.