General Science MCQs – Page 1 (Q1-10)

Force is measured in newtons (N) in the SI system, honoring Sir Isaac Newton for his laws of motion. One newton is the force needed to accelerate a 1 kg mass at 1 m/s squared, so 1 N equals 1 kg·m/s squared. Related SI units include the joule for energy, the watt for power, and the pascal for pressure, all named after pioneering physicists. Force is a vector quantity, meaning it has both magnitude and direction, unlike scalar quantities such as mass or speed.

Work and energy are both measured in joules (J), named after James Prescott Joule, who demonstrated the mechanical equivalent of heat in the nineteenth century. One joule equals the work done when a force of one newton moves an object one meter in the direction of the force. Common multiples include the kilojoule used in nutrition labels and the kilowatt-hour used for electricity billing. Power, by contrast, measures how quickly work is done and is expressed in watts, where one watt equals one joule per second.

Power, the rate of doing work or transferring energy, is measured in watts (W), named after Scottish engineer James Watt, who improved the steam engine. One watt equals one joule of energy transferred per second, and larger amounts are often expressed in kilowatts or megawatts. Watt’s work was so influential that the horsepower unit he popularized to market his engines is still used informally today, with one horsepower roughly equal to 746 watts. Electrical appliances typically display their power rating in watts.

Pressure is measured in pascals (Pa), named after French scientist Blaise Pascal, and is defined as one newton of force applied per square meter of area. Atmospheric pressure at sea level is about 101,325 pascals, often expressed as 101.3 kilopascals or one atmosphere. Other common pressure units include the bar, torr, and pounds per square inch (psi), frequently used in tire gauges and weather reports. Pascal also contributed to probability theory and built one of the earliest mechanical calculators.

Newton’s first law, often called the law of inertia, 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 external force. This concept was first hinted at by Galileo before Newton formalized it in his 1687 work Principia Mathematica. Inertia explains why passengers lurch forward when a car brakes suddenly and why a spinning top eventually slows only due to friction and air resistance. Newton’s three laws together form the foundation of classical mechanics.

Newton’s second law states that force equals mass times acceleration (F = ma), directly linking how hard something is pushed to how quickly its motion changes. This means a given force produces greater acceleration on a lighter object than on a heavier one, which is why a soccer ball accelerates faster than a bowling ball under the same kick. The law allows engineers to calculate the forces needed to launch rockets, stop vehicles, or design safe structures. It builds directly on the first law’s concept of inertia.

Newton’s third law states that for every action there is an equal and opposite reaction, meaning forces always occur in pairs acting on different objects. This principle explains how rockets propel themselves forward by expelling gas backward, and why swimmers push water behind them to move ahead. It also explains recoil in firearms and why walking is possible: your foot pushes backward on the ground, and the ground pushes you forward with equal force. Together with the first two laws, it completes Newton’s framework for classical mechanics.

Mass, a measure of the amount of matter in an object, is measured in kilograms (kg) in the SI system, making it the only base unit still historically tied to a physical artifact before 2019. Since 2019, the kilogram has been redefined using the Planck constant rather than a physical prototype kept in France. Mass should not be confused with weight, which is the force of gravity on an object and is measured in newtons, meaning your mass stays constant even though your weight changes on the Moon.

Length is measured in meters (m), originally defined in 1793 as one ten-millionth of the distance from the North Pole to the equator through Paris. Today the meter is defined precisely using the speed of light, as the distance light travels in a vacuum in 1/299,792,458 of a second. Common related units include the kilometer for large distances and the millimeter for small, precise measurements used in engineering and manufacturing. The meter is one of the seven fundamental SI base units.

Time is measured in seconds (s), currently defined using the extremely stable oscillations of cesium-133 atoms in atomic clocks rather than any astronomical event. This atomic definition, adopted in 1967, allows scientists to measure time far more precisely than using Earth’s rotation, which actually varies slightly. Seconds combine into minutes, hours, and days for everyday use, while GPS satellites rely on atomic clock precision to calculate location accurately. The second is one of the seven base units in the SI system.