What is the relationship between absolute pressure, gauge pressure, and atmospheric pressure?
ACS code: AM.I.J
Correct answer: Absolute pressure equals gauge pressure plus atmospheric pressure
Rationale: Gauge pressure is measured relative to ambient atmospheric pressure (a gauge reads zero when open to the atmosphere). To obtain absolute pressure, which is measured from a perfect vacuum, you add the atmospheric pressure to the gauge reading. The handbook's physics chapter defines absolute pressure as gauge pressure plus atmospheric pressure.
According to Boyle's law, if the volume of a confined gas is decreased while temperature is held constant, the pressure of the gas will
ACS code: AM.I.J
Correct answer: increase
Rationale: Boyle's law states that, at constant temperature, the pressure of a confined gas is inversely proportional to its volume (P x V = constant). Reducing the volume forces the same number of gas molecules into a smaller space, so they strike the container walls more often, raising the pressure.
Which statement correctly describes the heat transfer method known as convection?
ACS code: AM.I.J
Correct answer: Heat transfer by the circulation of a heated fluid or gas
Rationale: Convection is the transfer of heat by the movement of a heated fluid or gas; warmer, less dense fluid rises and cooler fluid moves in to replace it, creating circulation. Conduction is transfer through direct contact, and radiation is transfer by electromagnetic waves, so those describe the other two heat-transfer methods.
A first-class lever provides a mechanical advantage when the
ACS code: AM.I.J
Correct answer: effort arm is longer than the resistance arm
Rationale: Mechanical advantage of a lever equals the length of the effort arm divided by the length of the resistance arm. When the effort (force) arm is longer than the resistance arm, the ratio exceeds one, so a smaller applied force can move a larger resistance. Equal arms give a ratio of one (no advantage), and a shorter effort arm gives a ratio less than one.
What does the specific gravity of a substance compare?
ACS code: AM.I.J
Correct answer: The density of the substance to the density of water
Rationale: Specific gravity is the ratio of the density of a substance to the density of pure water, which is the standard reference. Because it is a ratio of two densities, it is a dimensionless number; a value greater than one means the substance is denser than water. Weight divided by volume defines density itself, not specific gravity.
According to Bernoulli's principle, as the velocity of a fluid moving through a tube increases, the static pressure of that fluid
ACS code: AM.I.J
Correct answer: decreases
Rationale: Bernoulli's principle states that within a flowing fluid, an increase in velocity is accompanied by a decrease in static pressure, because the total energy of the flow is conserved. As fluid speeds up through a constriction (a venturi), more of its energy is kinetic and less is in the form of static pressure.
Newton's first law of motion states that a body at rest tends to remain at rest, and a body in motion tends to remain in motion, unless acted upon by
ACS code: AM.I.J
Correct answer: an external force
Rationale: Newton's first law, the law of inertia, states that an object will not change its state of motion unless an unbalanced external force acts on it. Inertia is the property by which the body resists this change; it is not something that is lost, and mass does not spontaneously change, so the external force is the only correct cause.