ACT Science Practice Test 9

Metals differ in their relative abilities to conduct electricity. Resistance is a measurement in ohms (Ω) of how much a metal opposes electric current at a particular voltage.

A scientist performed 3 experiments using the circuit shown in Figure 1.

Figure 1

The metal resistor consisted of a coil of metallic wire with a known cross-sectional area and length (see Figure 2).

Figure 2

At the outset, the switch was open and no current flowed through the circuit. A 9-volt battery was used, and the black and red test leads of the circuit were attached to a metal resistor. When the switch was closed, electrons (negatively charged) flowed away from the negative battery terminal, through the circuit, and back to the positive battery terminal. The magnitude of current (charge per unit time) from this electron flow was measured by an ammeter, and was 1.0 × 10^-3 coulombs/second for the first trial of each experiment. The resistance (R) of the metal resistor was calculated in ohms (?) from the resulting values for voltage (V) and current (I).

Experiment 1

Three nickel resistor coils, each with a cross-sectional area of 7.61×× 10^-10 m² but with different lengths, were attached separately to the circuit. Results were recorded in Table 1.

Experiment 2

Three gold resistor coils of varying cross-sectional areas were tested. Each resistor coil had a measured length of 100 m. The results were recorded in Table 2.

Experiment 3

Three coils made of different metals were tested. Each resistor had a cross-sectional area of 2.67 × 10^-10 m² and a length of 100 m. The value ρ is related to each metal's inherent resistivity to current flow. Results were recorded in Table 3.

Pressure, temperature, volume, and amount of reactant are four variables that affect the rate at which a reaction in the gas phase occurs. A change in any of these variables changes the likelihood of particles running into each other and reacting: Increasing any one increases reaction rate; decreasing any one decreases reaction rate.

Pressure is measured in atmospheres, atm, where 1 atm is the sea level pressure of earth's atmosphere. Volume is measured in liters, L. The amount of reactant is measured in moles, where 1 mole is 6.02 × 10²³ molecules.

Figure 1 shows how temperature and pressure affect the gaseous reactants in an experiment. Figures 2 and 3 show how the rate of Reaction A is affected by pressure and temperature, respectively.

Figure 1

Figure 2

Figure 3

An experiment is set up to look at the physics of bouncing a ball, as shown in Figure 1.

Figure 1

When the ball is dropped, its initial velocity is 0 m/s. Velocity will increase until impact with the ground, at which point the ball's velocity immediately drops to 0 m/s again. After impact, velocity almost immediately increases to maximum post-impact velocity, and then begins to fall again as gravity works against it, slowing it down. The ball's velocity returns to 0 m/s when the ball is at its apex, or highest vertical point, post impact.

When a ball bounces, it deforms and becomes flatter. This is called elasticity. The more elasticity a material has, the better it is able to act like a spring and absorb force by being compressed, then use this force to "spring" back into the air. Post-impact velocity and the amount of time between velocity of 0 m/s at impact and velocity of 0 m/s at post-impact apex are affected by elasticity. Figure 2 shows the velocity of a ball versus time for balls with various elasticities and weights dropped from 1 meter height. Because gravity causes all objects to fall at the same speed regardless of weight, pre-impact velocities are identical for all balls.

Figure 2

A group of students studied the frictional forces involved on stationary objects.

In a series of experiments, the students used rectangular shaped objects of various materials that all had identical masses. One end of a plastic board coated with a polymer film was fastened to a table surface by a hinge so the angle θ between the board and table could be changed, as shown in Figure 1.

Objects were placed on the opposite end of the board, and the angle θ at which the object started to slide was recorded. The tangent of this angle represents the coefficient of static friction between the object and the polymer surface. This coefficient is proportional to the force required to move a stationary object. Higher coefficients mean that greater forces of friction must be overcome to initiate movement.

The dimensions of the objects gave them 3 distinct faces of unequal area as shown in Figure 2. Unless otherwise stated, the objects were placed on the ramp with Face A down.

Experiment 1

Four objects made of different materials were placed on the ramp at a temperature of 25°C. The ramp was gradually raised and as soon as the object started to move, the angle θ of the ramp was recorded in Table 1.

Experiment 2

The procedure for Experiment 1 was repeated with the wooden object, varying which face was placed down on the ramp. Results were recorded in Table 2.

Experiment 3

The procedure for Experiment 1 was repeated with the wooden object, varying the temperature of the polymer ramp. Results for 5 temperatures were recorded in Table 3.

Experiment 4

The procedure for Experiment 1 was repeated with multiple wooden objects. For each trial, the objects were stacked on top of each other before raising the ramp. The angle θ where the stack started to slide was recorded in Table 4.