1.
Part 1: Reading for Main Idea
Purpose: What causes a pendulum to move? What factors affect the motion of a pendulum?
A few definitions before you start:
Oscillation – a motion of moving back and forth at a regular interval
Period – the amount of time needed for one full oscillation; the time for an oscillating object to return to its start
Pendulum Measurements
Another method by which we can measure the acceleration due to gravity is to observe the oscillation of a pendulum, such as that found on a grandfather clock. Contrary to popular belief, Galileo Galilei made his famous gravity observations using a pendulum, not by dropping objects from the Leaning Tower of Pisa.
If we were to construct a simple pendulum by hanging a mass from a rod and then displace the mass from vertical, the pendulum would begin to oscillate about the vertical in a regular fashion. The relevant parameter that describes this oscillation is known as the period (time to make one full swing) of oscillation.
The reason that the pendulum oscillates about the vertical is that if the pendulum is displaced, the force of gravity pulls down on the pendulum. The pendulum begins to move downward. When the pendulum reaches vertical it can't stop instantaneously. The pendulum continues past the vertical and upward in the opposite direction. The force of gravity slows it down until it eventually stops and begins to fall again. If there is no friction where the pendulum is attached to the ceiling and there is no wind resistance to the motion of the pendulum, this would continue forever.
Because it is the force of gravity that produces the oscillation, one might expect the period of oscillation to differ for differing values of gravity. In particular, if the force of gravity is small, there is less force pulling the pendulum downward, the pendulum moves more slowly toward vertical, and the observed period of oscillation becomes longer. Thus, by measuring the period of oscillation of a pendulum, we can estimate the gravitational force or acceleration.
It can be shown that the period of oscillation of the pendulum, T, is proportional to one over the square root of the gravitational acceleration, g. The constant of proportionality, k, depends on the physical characteristics of the pendulum such as its length and the distribution of mass about the pendulum's pivot point (see equation to the right)
The small variations in pendulum period that we need to observe can be estimated by allowing the pendulum to oscillate for a long time, counting the number of oscillations, and dividing the time of oscillation by the number of oscillations. The longer you allow the pendulum to oscillate, the more accurate your estimate of pendulum period will be. This is essentially a form of averaging. The longer the pendulum oscillates, the more periods over which you are averaging to get your estimate of pendulum period, and the better your estimate of the average period of pendulum oscillation.
2.
What causes a pendulum's oscillating motion?
Correct Answer
C. The pendulum can't stop instantaneously, and once it does stop, it is pulled down by gravity, thus keeping it oscillating.
Explanation
The correct answer is that the pendulum can't stop instantaneously, and once it does stop, it is pulled down by gravity, thus keeping it oscillating. This explanation highlights the fact that a pendulum's oscillating motion is due to the combination of its inertia and the force of gravity. When the pendulum swings to one side, it has momentum that carries it to the other side, and gravity then pulls it back, causing it to continue oscillating back and forth. The force of friction and the amount of forces acting on the horizontal axis are not directly responsible for the pendulum's oscillating motion.
3.
What does oscillation mean?
Correct Answer
B. A motion of moving back and forth at a regular interval
Explanation
Oscillation refers to a motion of moving back and forth at a regular interval. It involves repetitive movement between two points, where an object or system continuously alternates between two extreme positions or states. This regular pattern of motion can be observed in various phenomena, such as pendulums swinging, sound waves, or the vibration of particles. The key characteristic of oscillation is the predictable and periodic nature of the back-and-forth motion.
4.
Which of the following best describes the behavior of a pendulum?
Correct Answer
D. If there is not friction nor air resistance acting on the pendulum, then it could swing forever.
Explanation
The correct answer states that if there is no friction or air resistance acting on the pendulum, then it could swing forever. This is because in the absence of external forces, such as friction or air resistance, the pendulum will continue to oscillate back and forth without any loss of energy. This is in accordance with the principle of conservation of mechanical energy, which states that in a closed system, the total mechanical energy remains constant. Therefore, the pendulum will continue to swing indefinitely without slowing down or stopping.
5.
How could you use the period (time for a full swing) of a pendulum to gather information?
Correct Answer
A. You could estimate the gravitational force or acceleration acting on the pendulum.
Explanation
The period of a pendulum is directly related to the gravitational force or acceleration acting on it. By measuring the time it takes for a full swing (period), you can use the equation T=2π√(L/g) to estimate the gravitational force or acceleration (g) acting on the pendulum. The length of the pendulum (L) can be measured, and by rearranging the equation, you can solve for g. Therefore, by using the period of a pendulum, you can gather information about the gravitational force or acceleration acting on it.
6.
Here is the formula for Period of oscillation (T). T describes the amount of time it takes to make a full swing. Look back in the text to answer the following question: Which of the following does play a role in the period of a pendulum?
Correct Answer
F. A, B & C
Explanation
The period of a pendulum is affected by the length of the pendulum, the distribution of mass in the pendulum, and the gravitational acceleration. These factors determine the time it takes for the pendulum to complete one full swing.
7.
By increasing the number of oscillations we are actually increasing our....
Correct Answer
B. Accuracy
Explanation
By increasing the number of oscillations, we are actually increasing the accuracy of our measurements. Accuracy refers to how close the measured value is to the true value. By increasing the number of oscillations, we are reducing the effects of random errors and improving the precision of our measurements. This means that the measured values will cluster closely around the true value, leading to a higher level of accuracy. Therefore, increasing the number of oscillations improves the accuracy of our measurements.
8.
The image above shows the graph received by physics students after allowing a pendulum to oscillate for some time. Using information gained from the passage, which of the following answers best identifies the likely IV and DV of this graph.
Correct Answer
D. IV = time, DV = distance from starting point
Explanation
As the x moves along (this is time), we see that there is an increase and then decrease in Y. We are seeing the movement of the bob as it falls towards y = 0 (meaning it is at the low point) and then rises (meaning it is moving to the high point of the swing) and then falls back down again.