Grade 8 Reading — Science

Chemical Reactions and the Law of Conservation of Mass

When wood burns in a campfire, ash remains and smoke drifts into the air. It might seem that matter has vanished. Yet chemists know that atoms are rearranged, not destroyed. The law of conservation of mass states that the total mass of reactants equals the total mass of products in a closed system. Understanding this principle helps engineers design safer fuels, factories, and environmental cleanup methods. A chemical reaction occurs when bonds between atoms break and new bonds form. Reactants are the starting substances; products are the new substances created. For example, when hydrogen gas reacts with oxygen gas, water forms. The hydrogen and oxygen atoms still exist—they simply combine in a different arrangement. Because no atoms disappear, the mass before and after the reaction stays the same if nothing escapes. Laboratory demonstrations make this law visible. Students might mix v…

Forces, Motion, and Newton's Laws

Objects move, stop, and change direction because forces act on them. Sir Isaac Newton described three laws of motion that still guide engineers building cars, rockets, and prosthetic limbs. These laws connect measurable quantities—mass, velocity, and acceleration—to everyday experiences such as riding a bus, throwing a ball, or braking a bicycle. Newton's first law states that an object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted on by an unbalanced force. In real life, friction and air resistance often act as unbalanced forces, which is why a sliding book eventually stops. Seat belts apply Newton's first law to safety: when a car suddenly stops, passengers keep moving forward until the belt applies a force to slow them. The second law links force, mass, and acceleration. A small force on a heavy truck produces little acceleration, …