Lab - Mechanics, Heat, and Sound (102M) - Experiment 1: Kinematics PDF

Lab - Mechanics, Heat, and Sound (102M) NAME: ______________________________________________ Experiment 1: Kinematics We encourage you to complete...

Lab - Mechanics, Heat, and Sound (102M) NAME: ______________________________________________ Experiment 1: Kinematics We encourage you to complete this lab using whatever equipment is available to you. There is no penalty for inaccurate measurements. Your grade is based on your reasoning about data that is collected and the rubric in the Assessment section of this Lab. If you are unable to set up the experiment and analyze data using available equipment, please contact your HS Instructor. Abstract The goal of this lab is to determine if the constant acceleration model accurately describes the motion of a falling object. A detailed procedure is provided, along with a worksheet to record your data and findings. Background In our first lab, we will be conducting an investigation of kinematic motion. Recall that kinematics is defined in the OpenStax College Physics textbook as “The study of motion without considering its causes.” Kinematic models are all the descriptions, equations, diagrams, etc. that we have used so far. These models relate a series of variables, like displacement, velocity, acceleration, and time, but do not say anything about why objects move. Later in this course, we will build other models to explore the various pushes and pulls that cause objects’ motion to change. Before we get to the investigation part of the lab, we will review motion with constant acceleration. Note that all models have limitations, and when you actually conduct your experiment they may or may not apply. Head’s up! Motion with Constant Acceleration In many physical situations, we find that objects move with a constant acceleration: that is to say, an acceleration which does not vary in time. Under this assumption of constant acceleration, here are four equations which relate the kinematic variables: v = v! + at. (L1.1a) 1 x = x! + v! t + at " (L1.1b) 2 v " = v!" + 2a (x − x! ) (L1.1c) Lab – Mechanics, Heat, and Sound (102M) | 1  Lab - Mechanics, Heat, and Sound (102M) NAME: ______________________________________________ 1 x = x! + (v! + v)t, (L1.1d) 2 where a is the acceleration, and x! and v! are defined as the initial position and initial velocity, respectively. In this lab, we will use this “constant acceleration” model to consider the motion of an object in free fall. While objects may possibly move in any direction with a constant acceleration, the easiest way to observe this in ordinary life is to study something moving vertically under only the influence of gravity. In this case, we take a = ±g, where g = 9.81 m/s" , and is a symbol representing the acceleration due to gravity at or near Earth’s surface. The plus or minus sign is needed to reflect a choice of a positive direction for a coordinate system. Materials List Quantity Lab Item Quantity Lab Item 1 Motion Detector 1 Ball 1 Ring Stand 1 Meter Stick Procedure The Procedure section describes the lab activity. Questions posed within this section should be addressed in the corresponding space on the worksheets at the end of this document. Be sure to record any thoughts, sketches, or data in the appropriate locations on the worksheets. For Experiment 1, you should expect to spend approximately 70-90 minutes to complete the investigation outlined below. Note: If motion detectors are not being used, you do not need to complete Part 1. Post-Lab questions may ask about the need for calibrating a motion detector, so please read and consider the purpose for calibration regardless of whether you need to do it. The questions on page 6 are not graded. Lab – Mechanics, Heat, and Sound (102M) | 2  Lab - Mechanics, Heat, and Sound (102M) NAME: ______________________________________________ Part 1: Get comfortable with the equipment For this experiment, you may be using the motion detector that you encountered in a previous activity. If so, your first task is to explore the characteristics and limits of your motion detector. If you are using a video recorder and the Tracker app, the calibration process described below does not apply. Typical motion detectors emit ultrasonic waves, which are sounds with frequencies higher than a human can hear. The detector uses the echo of the waves off an object to detect the position of the object in front of it, as shown in Figure 1. Often these detectors have multiple settings, such as a wide or narrow range, for detecting the motion of an object, as well as limits for how close or far away an object can be for an accurate measurement to be made. Figure 1. A motion detector is depicted as a speaker on the left, emitting sound waves, which are the red arcs moving towards the ball on the right. The dotted gray arcs are the waves bouncing off the ball and moving towards the detector. To ensure that the motion detector is recording accurate measurements, you are going to perform a calibration. This means that you will determine if the detector is recording accurate measurements (by verifying with a second, reliable instrument) and through observation. Complete the following steps: 1) Set up your motion detector to record distance and place it on a level surface. 2) Place some object in front of the detector and measure the distance from the object to the detector with a meter stick. 3) Turn on the detector and check the distance it is recording for the object. 4) Move the object closer to or further away from the detector and check its distance with both the motion detector and meter stick once more. 5) Now switch the settings of your motion detector to record velocity. 6) Use the meter stick to indicate a distance of one meter. 7) Try to move the object towards and away from the detector at a steady speed. Using a timer or simply counting, estimate the time that it takes to move the object one meter. If you count 2 seconds to move the object 1 meter, then you would expect to see a velocity of 0.5 m/s. Verify that the velocity displayed is sensible. Consult with your instructor if you are unsure whether the detector is providing accurate readings. Lab – Mechanics, Heat, and Sound (102M) | 3  Lab - Mechanics, Heat, and Sound (102M) NAME: ______________________________________________ Part 2: Constant acceleration? You will be exploring if the constant acceleration model accurately describes the motion of a falling object. If you are using a motion detector, set it up similar to what is shown in Figure 2A, so that its detector face is oriented vertically (give yourself as much vertical distance for dropping objects as you can). If you experience difficulty in recording position versus time as the ball falls, check the settings on your motion detector (consult your instructor before doing this). If you are not using a motion detector, set up your video recorder similar to what is shown in Figure 2B so that it can record the entire motion of the object from a stationary position. Figure 2. A) A motion detector is positioned above a ball being dropped. The detector emits ultrasonic waves in the direction of the ball. B) A smartphone camera is positioned to record the changing position of a ball being dropped from a particular height. Using a ball or other object that is unlikely to break when dropped, complete the following steps: 1) Predict whether you think the free fall (constant acceleration) model will accurately describe the motion of this particular object when dropped. 2) Hold the object as high as possible, in line with your detector or in view of your video recorder. 3) Release the object from rest, and let it fall until it hits the ground. Your motion detector or video recorder should be collecting data for the span of time from the release of the object until it strikes the ground. 4) Determine the time interval for which the object is freely falling. 5) Using either the motion detector output or a video analysis app (see materials for suggestions), record 10 data points (position and time) during this interval. 6) Repeat this process, recording data each time, for up to four more trials. As a group, examine the data you collected and determine whether the free fall constant acceleration model accurately describes the motion of the object that you dropped. Record your conclusions in the space provided on the data sheet. Lab – Mechanics, Heat, and Sound (102M) | 4  Lab - Mechanics, Heat, and Sound (102M) NAME: ______________________________________________ Assessment This section summarizes information regarding the assessment of Post- Lab 1. The worksheets for this lab should be scanned or photographed and uploaded as part of the post-lab assignment in the college Canvas course. Please make sure that you are familiar with each scientific ability that we are looking for, and check that your work addresses them. For question 1, refer to Part 1: Getting comfortable with the equipment. Question 1 (NOT GRADED) 1. In measuring the distance between the motion detector and an object, what do you observe about how accurate the distance displayed on the motion detector is? 2. In measuring the velocity of an object, what do you observe about how accurate the velocity displayed on the motion detector is? 3. What could (or did) you do to improve the accuracy of the motion detector? For questions 2-6, refer to Part 2: Constant acceleration. Question 2 (10 pts) Identify the type of object that your group dropped (brief description and size) and predict whether the free fall constant acceleration model will accurately describe its motion. Lab – Mechanics, Heat, and Sound (102M) | 5  Lab - Mechanics, Heat, and Sound (102M) NAME: ______________________________________________ The tables below are assessed using the following rubrics. Needs some Scientific Ability Adequate (10) Inadequate (3) Missing (0) improvement (7) There are There are sufficient There are There are no measurements for measurements of measurements for repeated Repeats the same set of all parameters for different, measurements for measurements conditions, but the the same set of unrelated sets of the same set of number is conditions. conditions. conditions. insufficient. Needs some Scientific Ability Adequate Inadequate Missing improvement The description of Communicates Clearly and The findings are the findings is findings of the accurately discussed, but No discussion of communicated, experiment describes what vaguely or with the findings is but incomplete or completely and happens in the major inaccuracies present. inaccurate in clearly. experiments. or omissions. places. Question 3 Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 t (s) y (m) t (s) y (m) t (s) y (m) t (s) y (m) t (s) y (m) 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 6 6 6 6 6 7 7 7 7 7 8 8 8 8 8 9 9 9 9 9 10 10 10 10 10 Lab – Mechanics, Heat, and Sound (102M) | 6  Lab - Mechanics, Heat, and Sound (102M) NAME: ______________________________________________ In later labs, we may ask you to analyze all of your data trials, but in the questions below we will ask you to just focus on one trial. Question 4 (5 pts). Analyze your data to determine if acceleration is constant for one of your data trials. Complete calculations for at least three time intervals within that trial. We will assume that the results from these three time intervals are representative of the entire trial. One way to do this is to use the kinematics equations in the Background, but there are other methods possible. Question 5 (5 pts) Create a graph of one data trial. You may create your graph in one of many ways. You may: 1) plot your data points by hand using the graphing space below; 2) create a graph using graphing software, such as Excel or Google Sheets; or 3) take a screenshot of your graph created by data collection software, such as Vernier. Regardless of how you create your graph, it must include a title to indicate which Trial is graphed, properly labeled axes, and individual data points must be shown. For instructions and best practices in hand graphing or using Excel and Google Sheets, please reference the Graphing Resources in your College Canvas Lab course, which is under Lab Resources in the first tile. Lab – Mechanics, Heat, and Sound (102M) | 7  Lab - Mechanics, Heat, and Sound (102M) NAME: ______________________________________________ Title: Position (meters) Time (seconds) Question 6 (5 pts). In a few sentences describe observations about your graph and what conclusions can be drawn. Include observations about the shape of the graph. For example, is it linear or does it curve? Is the slope positive or negative? Then, consider what this might mean about the motion of the object. Does it indicate increasing, decreasing, or constant acceleration? How do you know this? Lab – Mechanics, Heat, and Sound (102M) | 8