Tag: science & technology

The iris is the colored part of the eye that contains muscles to control the size of the pupil, regulating light entering the eye. The cornea is the clear front surface, the pupil is the black opening in the center, and the lens focuses light behind the pupil.

A catheter is a flexible tube inserted into the body to inject fluids (like medication) or withdraw fluids (like urine or blood). It is commonly used in medical procedures for drainage, administration of treatment, or diagnostic purposes.

Momentum is defined as the product of an object's mass and its velocity (p = mv). This is a fundamental concept in physics describing the quantity of motion. Energy, Force, and Acceleration are related but distinct quantities - Energy is 1/2 mv^2 for kinetic energy, Force equals mass times acceleration (F=ma), and Acceleration is the rate of velocity change.

Albert Einstein developed the Theory of Relativity, published in 1905 (Special Relativity) and 1915 (General Relativity). Isaac Newton developed classical mechanics and gravity, not relativity. Marie Curie discovered radioactivity and polonium/radium. Benjamin Franklin was a statesman and scientist known for electricity experiments, not relativity.

Mercury orbits fastest because it's closest to the Sun (about 58 million km vs Earth's 150 million km). According to Kepler's laws, orbital speed decreases with distance. Mercury's average orbital speed is about 47.9 km/s, compared to Earth's 29.8 km/s. Saturn and Uranus are much farther and slower; Mars averages 24.1 km/s.

The liver is the largest internal organ by weight, averaging 1.4-1.6 kg in adults. It performs vital functions including detoxification, protein synthesis, and bile production. The skin is actually the largest organ overall by weight and surface area, but among internal organs listed, the liver dominates. The brain weighs about 1.3-1.4 kg, making it second among internal organs.

For a nut failing due to thread shear, the shear area is calculated as the circumference of the thread (pi x d) multiplied by the thickness of the nut (t). So A_shear = pi x d x t = 3.14 x 12 x 10 mm^2. This represents the cylindrical surface area of the threads that shears. Options A, C, and D use incorrect formulas.

In bolt grading systems like ISO 898, class 12.9 means: 12 = ultimate tensile strength (1200 MPa minimum, first digit × 100), 9 = yield strength ratio (90% of ultimate tensile strength, second digit × 10%). This is standard mechanical engineering notation for bolt strength properties.