ACT Aspire Science (Grade 8)

PASSAGE Sound is a series of vibrations moving through a medium such as air or water. Sound travels as longitudinal waves that transmit kinetic energy through the medium. This energy is transmitted particle to particle in a series of compression and rarefaction pulses. Sound can travel through solids, liquids, and gases, but cannot travel through a vacuum. The speed of sound through a material depends on specific factors, including the state of matter of the material, the elasticity of the material, and the density of the material. Sound generally travels faster through solids than liquids and gases, because the particles are much closer together in a solid than in a liquid or gas. Sound generally travels faster in a more elastic medium, because the particles are better able to return to their original positions, making them available to transmit the energy of the next pulse. Sound generally travels slower in a medium of higher density, because high-density materials typically have larger and heavier particles that move slower. See Table 1.

Which of the following statements is not true?

• The elasticity of a medium affects the speed of sound.

• Sound travels faster through sea water than water.

• The temperature of air has no effect on the speed of sound.

• The speed of sound is greater in solids than liquids.

PASSAGE Sound is a series of vibrations moving through a medium such as air or water. Sound travels as longitudinal waves that transmit kinetic energy through the medium. This energy is transmitted particle to particle in a series of compression and rarefaction pulses. Sound can travel through solids, liquids, and gases, but cannot travel through a vacuum. The speed of sound through a material depends on specific factors, including the state of matter of the material, the elasticity of the material, and the density of the material. Sound generally travels faster through solids than liquids and gases, because the particles are much closer together in a solid than in a liquid or gas. Sound generally travels faster in a more elastic medium, because the particles are better able to return to their original positions, making them available to transmit the energy of the next pulse. Sound generally travels slower in a medium of higher density, because high-density materials typically have larger and heavier particles that move slower. See Table 1.

Which of the following best describes sound waves?

• Sound is a series of longitudinal waves traveling through an elastic medium.

• Sound is a series of transverse waves traveling through an elastic medium.

• Sound is a series of longitudinal waves traveling through a vacuum.

• Sound is a series of transverse waves traveling through a vacuum.

PASSAGE Sound is a series of vibrations moving through a medium such as air or water. Sound travels as longitudinal waves that transmit kinetic energy through the medium. This energy is transmitted particle to particle in a series of compression and rarefaction pulses. Sound can travel through solids, liquids, and gases, but cannot travel through a vacuum. The speed of sound through a material depends on specific factors, including the state of matter of the material, the elasticity of the material, and the density of the material. Sound generally travels faster through solids than liquids and gases, because the particles are much closer together in a solid than in a liquid or gas. Sound generally travels faster in a more elastic medium, because the particles are better able to return to their original positions, making them available to transmit the energy of the next pulse. Sound generally travels slower in a medium of higher density, because high-density materials typically have larger and heavier particles that move slower. See Table 1.

Which of the following statements is generally true?

• Sound travels at the same speed in all states of matter.

• Sound travels faster in gases than in liquids and solids.

• Sound travels faster in liquids than in solids and gases.

• Sound travels faster in solids than in liquids and gases.

EXPERIMENT Students studied the effect of the density of sound barriers on the transmission of sound. Students built a plywood box with a removable front. Students made fronts of plywood, plastic, glass, and marble tile. The fronts all had the same thickness. The densities of these materials were recorded in Table 2. Students measured the decibel level of a siren at a distance of 40.0 cm at 90 decibels. Students then placed the siren inside the box. The decibel meter was placed in front of the box at distance of 40.0 cm from the siren that was located inside the box. The decibel level was measured for each box front, and the data was recorded in Table 2.

How loud was the siren when tested before it was placed in the box?

• 100 dB

• 200 dB

• 40 dB

• 90 dB

In the savannas of South Africa, a black rhinoceros and a parasite-eating bird called the oxpecker share an interesting relationship. The oxpecker eats the horsefly larvae, ticks, and other parasites embedded in the rhinoceros's hide, and warn the rhino of danger.

What type of feeding relationship do the rhinoceros and oxpecker share?

• Competition

• Parasitism

• Commensalism

• Mutualism

The great blue heron is a huge wading bird found in Florida. Great blue herons usually eat small fish but may eat shrimp, crabs, and many types of other organism. What is the feeding relationship between the great blue heron and the fish it eats?

• Competition

• Parasitism

• Predator and prey

• Commensalism

Passage

Electric current flows through some materials more readily than others. Materials that conduct electricity are called conductors. Materials which do not conduct electricity are insulators. Good conductors include copper, gold, silver, and aluminum. Good insulators include air, plastic, rubber, and wood. In metal conductors, the electrons are free to flow down the center of the lattice structure of the metal. But even in a good conductor, there is a small resistance. The resistance of a material is the amount of hindrance to electron flow. Resistance in conductors depends on factors such as type of material, the diameter of the conductor, the length of the conductor, and the temperature. Superconductors are materials that have no electrical resistance at extremely low temperatures. Electrical conductivity is the ability of a material to conduct current. Electrical conductivity and resistance are inversely related. The greater the resistance of a material, the lower the electrical conductivity of the material. Ohm's law states the mathematical relationship between voltage, current, and resistance. According to Ohm's Law, voltage is the product of current and resistance. The units of voltage, current, and resistance are volts, amperes, and ohms, respectively. Multimeters (see Figure 1) have multiple settings that can measure the voltage, current in a circuit, and resistance of a conductor. The voltmeter setting measures voltage in volts. The ammeter measures current in amperes. The ohmmeter measures resistance in ohms.

According to this passage, which of the following does not affect the resistance of a wire?

• Diameter of the wire

• Length of the wire

• Temperature

• Atmospheric pressure

According to the results in Table 1, what is the effect of temperature on the current flowing through the copper wire?

• As the temperature of the wire increased, the current of the wire increased.

• As the temperature of the wire increased, the current of the wire decreased.

• As the temperature of the wire increased, the current of the wire remained the same.

• As the temperature of the wire increased, the current of the wire fluctuated.

According to the results in Table 1, what is the effect of temperature on the resistance of a copper wire?

• As the temperature of the wire increased, the resistance of the wire increased.

• As the temperature of the wire increased, the resistance of the wire decreased.

• As the temperature of the wire increased, the resistance of the wire remained the same.

• As the temperature of the wire increased, the resistance of the wire fluctuated.

Which planet has the shortest period?

• Earth

• Jupiter

• Mercury

• Neptune