ASVAB Science And Tech Practice Questions

Explanation
The correct answer is Neuron. The unit of the nervous system is a neuron. Neurons are specialized cells that transmit information through electrical and chemical signals. They are responsible for the processing and transmission of information in the nervous system, allowing for communication between different parts of the body.

Explanation
Adrenaline is known as the emergency hormone because it is released in response to stress or danger. It prepares the body for a "fight or flight" response by increasing heart rate, blood pressure, and energy levels. This hormone helps to mobilize the body's resources and enhance physical performance in stressful situations. Cortisol also plays a role in stress response, but adrenaline is specifically associated with the immediate physiological changes that occur during an emergency situation. Insulin and thyroxine are not directly related to the body's emergency response.

Explanation
Scissors is not a type of teeth because it is a tool used for cutting, while the other options (premolar, molar, incisor) are types of teeth found in the human mouth.

Explanation
A wind vane is a device used to measure wind direction. It consists of a freely rotating arrow or vane that aligns itself with the direction of the wind. The vane is usually mounted on a vertical rod or spindle, allowing it to rotate easily. By observing the direction in which the vane points, one can determine the wind direction. Anemometer, barometer, and hygrometer are instruments used to measure wind speed, atmospheric pressure, and humidity respectively, but not wind direction.

Explanation
Sublimation is the process in which a solid directly changes into a gas without passing through the liquid phase. This occurs when the pressure and temperature conditions are such that the solid's vapor pressure exceeds its surrounding pressure. During sublimation, the solid particles gain enough energy to overcome the intermolecular forces and escape into the gas phase. Examples of substances that undergo sublimation include dry ice (solid carbon dioxide) and mothballs (naphthalene).

Explanation
Glass is not considered a simple machine because it does not possess any mechanical advantage or help in the transfer of energy. Simple machines are typically defined as devices that make work easier by either changing the direction or magnitude of a force. Pulley, wedge, and inclined plane are all examples of simple machines as they are designed to reduce the effort needed to perform tasks. However, glass is a material and not a mechanical device, thus it does not fall under the category of simple machines.

Explanation
Calcium is the correct answer because it is a vital nutrient that plays a crucial role in bone health and proper formation. It is a major component of bone tissue and helps to build and maintain strong bones. Calcium is necessary for the development and maintenance of healthy teeth as well. It also plays a role in muscle function, nerve transmission, and blood clotting. Therefore, consuming an adequate amount of calcium through diet or supplements is essential for promoting bone health and preventing conditions like osteoporosis.

Explanation
Friction is the force that opposes the motion of objects in contact with each other. When two surfaces rub against each other, it creates friction, which causes wear and tear in machines over time. The constant rubbing and sliding of machine parts against each other leads to the erosion of materials, loss of efficiency, and eventual breakdown of the machine. Therefore, friction is the primary cause of wear and tear in machines.

Explanation
Mass is a scalar quantity because it only has magnitude and no direction. Scalar quantities are described by a single numerical value, such as mass, temperature, or time. In contrast, velocity, momentum, and impulse are vector quantities because they have both magnitude and direction.

Explanation
The first generation of computers made use of vacuum tubes. Vacuum tubes were electronic components that controlled the flow of electricity in early computers. They were large, fragile, and generated a lot of heat, requiring frequent maintenance. Despite their limitations, vacuum tubes were a major breakthrough in computer technology and allowed for the development of the first electronic digital computers.