Marty Greco, Larry Leung,

Transcription

1 Science on the Move Physics Lab # P2B I. TEACHER NOTES & GUIDELINES TITLE OF LAB - Introduction to Motion DEVELOPERS OF LAB - Adele Rawson, JD736@maristb.marist.edu Marty Greco, JD891@maristb.marist.edu Larry Leung, JD728@maristb.marist.edu ADAPTED FROM A LAB BY - John G. Lane, Rita R. Langva, Taylor A. Pancoast OVERVIEW OF LAB DESCRIPTION: This lab provides the students with the opportunity to explore the interrelationship of position vs. time and velocity vs time graphs and develop the concept of the acceleration vs time graph in comparison to the students expectations. It also exposes the students to the error that can occur in instrumental measurement of motion and analyze a graph that is not correct. CURRICULUM CONSIDERATIONS: This lab will be best applied to the unit of Kinematics where the students are developing the concept of describing and measuring motion after the concept of constant velocity has been studied and before the study of freefall. SAFETY CONSIDERATIONS : 1. Standard Electrical Safety with 120 V Wall Sockets. 2. Food/Drink should not be used near the equipment. 3. Always place the carts upside down when the carts are not in use because the carts can roll off a table and be damaged or cause injury. 4. Do not place equipment ON the track. Damage can occur to the track surface affecting lab results. BACKGROUND INFORMATION A. SCIENTIFIC VIEWPOINT: Interrelationship between position, velocity, acceleration and time. Student skills include measurement of position and time, plotting relationships and relating axes, recognition of direct vs exponential relationships. B. COMMON MISCONCEPTIONS IF Velocity is zero (0), THEN Acceleration is zero (0). IF Velocity is greater than zero (>0), THEN Acceleration is greater than zero (>0). IF Velocity is large, THEN Acceleration is large. Acceleration is ALWAYS 9.8 m/s 2. Acceleration at the peak of a trajectory is 0. The bigger the bounce of the cart, the greater the Acceleration. On a graph the CHANGE of position is ALWAYS positive.

2 NEGATIVE ACCELERATION means the object is moving BACKWARDS. OBJECTIVES - Content - SWBA to graphically describe motion with changing velocity, make distinctions between position/time, velocity/time and acceleration/time graphs, and understanding on independent and dependent variables. Skills - Measurement of position and time using the SOTM/PASCO equipment and then be able to apply these skills on a related student defined situation. Attitudinal - Students will be able to develop confidence in predicting graphs of objects in motion, and discerning valid and invalid data. S's will also develop confidence in using given technology to perform measurement to verify there predictions. EQUIPMENT/MATERIALS PROVIDED BY SOTM: 1. Pasco Scientific Interface Computer 3. Motion Sensor 4. Linear Track 5. Spring cart 6. Ring stand and clamps PROVIDED LOCALLY: 1. Level Lab Tables 2. (2) AC Power Outlets per Lab Group ADVANCE PREPARATION The connections between the interface and both the computer and the motion sensor for each set-up are best done before the lab starts. You will have to tell the students how to turn on the computer (push the white tab on the back left side of the laptop towards the back of the computer). See illustration below.

3 II. PRE-LAB PRE-LAB EXERCISE TO ELICIT STUDENTS' PRIOR KNOWLEDGE AND MISCONCEPTIONS 1. Have students complete pre-lab questionnaire. 2. Model an example of a dynamics cart moving at constant velocity. 3. Have the students describe the motion using descriptive words like; position, initial velocity, final velocity, speed, time, and acceleration. 4. Have students develop a sketch of their impressions of a position-time graph and velocity-time graph, and an acceleration-time graph for the motion of the dynamics cart moving at constant velocity. DISCUSSION OF PRECONCEPTIONS 1. Have students put graphs on the board, followed by a class discussion on whether or not the graphs are correct or incorrect, providing reasons why. During the discussion, the teacher should help the students to identify why the graphs are incorrect, trying at this point to correct any misconceptions. 2. The goal of this exercise is to make students aware of the different ideas held by other students pertaining to motion, velocity and time. This is a time where the teacher can direct the students to develop more appropriate reasoning which will allow them to make correct predictions of motion graphs. 3. Demonstrate the use of the motion detectors and PASCO computer equipment to verify their predictions of the motion graphs. III. EXPLORATION OF SCIENTIFIC PRINCIPLE & INTRODUCTION OF EXPERIMENTAL PROTOCOL PROBLEM Students will be able to predict the graphical outcomes and interrelationships between motion graphs of the one required experiment and at least one student defined example of motion. EXPERIMENT AND TECHNICAL OPERATION OF EQUIPMENT (Student Edition) PROCEDURE: Set up the ramp with the end stop at the lower end and the upper end about 12 cm high, using the ring stand and pivot clamp block. Also mount the motion sensor on the ring clamp so it is just above the level of the ramp and pointing toward the lower end of the ramp. Press the spring plunger all the way into the cart and latch it, placing the cart at the bottom of the ramp with the rod against the end stop. Start. the cart by gently tapping the trigger with another

4 rod or ruler until it unlatches and propels the cart up the ramp. Adjust the ramp height until the cart gets no closer than 40 cm to the motion sensor. In this experiment you will be representing your motion with 3 different types of graphs utilizing a motion sensor connected to a computer. Position vs. Time.- Activity # 1 Position vs. Time graph Before using the motion sensor, predict what the motion should look like by sketching a graph on the position versus time axis provided in Graph Set A. Activity # 2 - Making the position vs. Time graph TO USE THE COMPUTER: Double click on the Science Worksbop icon on the desktop of the computer. Click on the appropriate interface (300, 500 or 700). Click on OK or hit enter. "Click and drag" the digital plug to digital channel 1 (a new screen will pop up). Then click on the motion sensor 'icon. (Both digital channels on the interface picture will now have a white box around them). Click and drag the graph icon to the white to box around channel 1 (a new pop up appears). Select position x and hit. Enter. You will be recording the motion of the cart from the time you trigger the spring plunger until at least three bounces of the cart from the end stop. Science Workshop program,will plot your motion on a position time graph. When you are ready to begin, put the pointer on the REC button, and click (you will hear the motion sensor clicking if all is well.). To stop recording data, put the pointer on STOP and click. With the motion sensor on, perform the cart motion you have predictions for. After the data collection, click on the auto scale icon (top furthest right icon of those icons in the lower left corner of the graph box to properly display the computer graph. Record (draw) the computer generated graph on the Graph set B of position versus time axes provided for each motion on your second data sheet. Activity #3 - Comparing predictions to data. Use the blank space provided on your data sheet to compare your predictions to the computer generated graphs and explain any differences between the two. Velocity vs. Time : Activity #4 - Predicting velocity vs. Time graph. Predict what the velocity versus time graph should look like by sketching a graph on the first velocity versus time axes provided in Graph set A. Activity #5 - Making the velocity vs. time graph

5 To change the type of graph shown by the computer for your motion, on the upper left square of the graph's active window (contains a circle, a triangle and a motion sensor icon). A new screen will pop up, put the cursor on digital 1 and another screen will pop up. Move your mouse to the right and click on Velocity. You now have a graph of velocity versus time for that data. Record that graph on Graph set B of velocity versus time axes provided. Activity #6 - Comparing predictions to data. Use the blank space provided on your data sheet to compare your predictions to the computer generated graphs and explain any differences between the two. Acceleration vs. Time : Activity #7 - Predicting the acceleration time graph. Now predict what the acceleration versus time graph should look like by sketching a graph on the first of the two velocity versus time axes provided Activity #8 - Making the acceleration vs. time graph. To change the type of graph shown by the computer for your motion, click on the upper left square of the graph's active window (contains a triangle and a motion sensor icon). A new screen will pop up, put the cursor on digital 1 and another screen will pop up. Move your mouse to the right and click on acceleration. You now have a graph of acceleration versus time for that data. Record that graph on the Graph set B of acceleration versus time axes provided. Activity #9 - Comparing predictions to data. Use the blank space provided on your data sheet to compare your predictions to the computer generated graphs and explain any differences between the two. See graph sets A and B in appendix. IV. ELABORATION OF SCIENTIFIC PRINCIPLE: INQUIRY-BASED STUDENT INVESTIGATION PROBLEM Students to define a motion experiment that can be measured using the SOTM equipment. Students must make a prediction of their graphs prior to performing their experiment. They must develop and write a procedure for performing their experiment and develop a convenient method of displaying their data. Their graphs and interpretations will be the final results of the experiment. Examples of possible student motion experiments Objects in freefall Differing angles of the Linear Track Changing masses of the Dynamics Cart Bouncing Ball Pendulum

6 HYPOTHESIS OR PREDICTION From the information you have about this topic, develop a hypothesis that could be tested in a controlled experiment that will gather quantitative data. Explain the reasoning behind your hypothesis. EXPERIMENTAL DESIGN The following series of questions will help you define the parameters of the laboratory experiment. You must complete the answers and submit to the teacher before proceeding. 1. What example(s) of motion do you plan to investigate? 2. Which variables are important to what you plan to measure? 3. Are you able to make the measurements indicated in number 2? 4. What factors would you want to control? 5. How will you organize your data? 6. What do you believe your graphs will look like? Checkpoint (Teacher checks students' experimental design for feasibility.) PLAN FOR DATA COLLECTION & ANALYSIS Materials per group: Procedures for your team: Results: Checkpoint (Teacher checks students' plan for feasibility.) CONDUCTING THE EXPERIMENT Teacher supervises and assists if necessary, in operation or use of supplies. Checkpoint (Teacher monitors students' investigations in progress.) ANALYSIS OF DATA Students develop and interpret graphs using data collected in this experiment. Students must qualify and quantify the meanings of graphical slopes, identify appropriate units, and directions of motion. Checkpoint (Teacher checks students' analysis.) DISCUSSION OF RESULTS COMPARE 1. Do the results of the graph(s) of the experiment support your initial hypothesis? 2. If your graphs do not completely agree with your predictions, which parts are similar and which are not similar?

7 3. Give evidence why the predictions did not agree with your results. 4. What other types of errors could have affected your experiment?. PERSUADE 1. Teacher shows a diagram of a position/time graph on the board or on the overhead screen. Students are directed in groups to write on white boards or the computer a description of the motion and why they chose their description. 2. Teacher mediates discussion between students until students arrive at a general consensus on their belief as to an acceptable answer. Teacher can help guide groups through questioning only. RELATE 1. Teacher models a motion of a real life situation. Have student groups predict results. V. EVALUATION POST-LAB SURVEY OF STUDENTS' CONCEPTIONS Have students retake the Pre-Lab Exercise. Compare pre-lab and post-lab responses. TRADITIONAL Select ten short answer or multiple choice questions applicable to content covered throughout the lab to administer after the completion of this lab. ALTERNATIVE Each student will decide on an individual motion and sketch all three graphs, including quantities of the variables. The students will then perform the task in front of the motion detector without seeing the screen. Students will be evaluated as to the accuracy of their motion to their predictions based upon the following scoring rubric. Response Scale 4-Excellent Response: Response would be the student's ability to relate the their motion to all three graphs, meeting all time, distance and velocity parameters. Language expression is clear, addresses the question, and for the most part obeys conventions of punctuation, sentence structure and spelling. 3-Good Response: Student's show the ability to relate motion to three graphs, and does not meet all quantified parameters. Language expression is clear and unambiguous and addresses the question, but may or may not obey conventions of spelling, sentence structure, or punctuation. 2- Adequate Response: Student is able to create and identify the motion, but is unable to relate to the three motion graphs. Language expression may be decipherable, but may be poor.

8 1-Inadequate Response: Student response includes an error in fact about the description of motion of one of the graphs. Student can construct graph axes correctly, but data does not represent the motion. Language expression is not considered in this level. This material is based upon work supported by the National Science Foundation under Grant No. ESI Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.