General Science MCQs – Page 8 (Q71-80)

A spring balance is commonly used to measure weight or force, working on the principle that the extension or compression of a spring is proportional to the force applied to it, as described by Hooke's law. Because it measures force directly, a spring balance would give different readings for the same object on Earth versus the Moon, since weight depends on local gravity, unlike mass. Spring balances are widely used in simple laboratory experiments, fishing scales, and some kitchen and luggage scales.

A beam balance, also called an equal-arm balance, is commonly used to compare and measure mass by balancing an unknown mass against known standard masses on opposite sides of a pivoting beam. Because it compares two masses against each other rather than measuring force directly, a beam balance gives the same reading for an object's mass regardless of location, whether on Earth or the Moon, unlike a spring balance which measures weight. This makes beam balances the preferred instrument in chemistry and precision laboratory work where accurate mass measurement is essential.

Galileo Galilei is credited with early, groundbreaking experiments on the law of falling bodies, demonstrating that objects of different masses fall at the same rate in the absence of air resistance, contradicting the earlier Aristotelian belief that heavier objects fall faster. He reportedly used rolling balls down inclined planes to slow motion enough for careful measurement, since accurate timing devices for free fall did not yet exist. Galileo's work laid essential groundwork for Isaac Newton's later, more comprehensive laws of motion and universal gravitation, earning him recognition as a father of modern experimental science.

Isaac Newton is credited with formulating the three fundamental laws of motion, published in his 1687 masterwork Philosophiae Naturalis Principia Mathematica, which also introduced his law of universal gravitation. These laws, covering inertia, the relationship between force, mass and acceleration, and action-reaction pairs, became the foundation of classical mechanics for over two centuries until refined by Einstein's relativity for extreme speeds and scales. Newton was also a pioneer in optics and mathematics, co-inventing calculus independently alongside Gottfried Leibniz, making him one of history's most influential scientists.

Archimedes' principle states that the buoyant force on a submerged or floating object equals the weight of the fluid it displaces, explaining why objects float, sink, or hang suspended depending on how their density compares to the surrounding fluid. According to legend, Archimedes discovered this principle while stepping into a bath and noticing the water level rise, then famously ran through the streets shouting Eureka. This principle explains why massive steel ships float, since their overall shape displaces enough water to equal their weight, and it underlies the design of submarines, hot air balloons, and hydrometers.

An object floats in a fluid when its overall density is less than the density of the fluid, allowing the buoyant force to fully support its weight before it becomes completely submerged. This relationship follows directly from Archimedes' principle, which states that the upward buoyant force equals the weight of fluid displaced by the object. Wood floats on water because it is less dense, while a steel nail sinks despite steel ships floating, since a ship's hull shape displaces enough water to give it a low overall density. Submarines adjust their average density using ballast tanks to control whether they float, sink, or hover.

Pascal's law correctly states that pressure applied to an enclosed, incompressible fluid is transmitted undiminished and equally in all directions throughout the fluid. This principle, discovered by French scientist Blaise Pascal in the seventeenth century, explains why hydraulic systems can multiply force: a small force on a small piston creates pressure that also acts over a much larger piston, producing a much larger output force. Hydraulic brakes, jacks, and lifts all rely on this principle to move heavy loads with modest input force. Liquids are used rather than gases in such systems because liquids are essentially incompressible.

Hydraulic presses and hydraulic brake systems operate on Pascal's law, which states that pressure applied anywhere in an enclosed incompressible fluid is transmitted equally throughout the fluid. In a hydraulic press, a small force applied to a narrow piston creates pressure that acts equally on a much wider piston, producing a greatly amplified output force, since force equals pressure multiplied by area. Car brake systems apply the same principle, letting a light push on the brake pedal generate enough force at each wheel to stop a heavy vehicle. This differs from Bernoulli's principle, which concerns fluids in motion rather than pressure transmission in static fluids.

Bernoulli's principle describes the inverse relationship between the speed of a moving fluid and the pressure it exerts, meaning that as a fluid's velocity increases, its pressure decreases, and vice versa. Formulated by Swiss mathematician Daniel Bernoulli in the eighteenth century, the principle stems from the conservation of energy within a flowing fluid. It explains how airplane wings generate lift, since air moving faster over the curved upper surface exerts less pressure than the slower air beneath. Bernoulli's principle also explains why shower curtains billow inward and why perfume atomizers draw liquid upward into a fast air stream.

According to Bernoulli's principle, a faster-moving fluid exerts lower pressure than a slower-moving one, since the fluid's kinetic energy increases at the expense of its pressure energy when total mechanical energy along a streamline stays constant. This inverse relationship explains numerous everyday phenomena, from the lift generated on an airplane wing to why a shower curtain gets pulled inward when water starts flowing. It also explains the venturi effect, where fluid speeds up and pressure drops while passing through a narrowed section of pipe, a principle used in carburetors and flow meters. Aerodynamic design relies heavily on this pressure-speed relationship.