SOTM LAB: P5R Forces and Motion I. TEACHER NOTES & GUIDELINES TITLE OF LAB. Forces and Motion (with a 1.2m track and smart pulley) DEVELOPERS OF LAB

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1 SOTM LAB: P5R Forces and Motion I. TEACHER NOTES & GUIDELINES TITLE OF LAB Forces and Motion (with a 1.2m track and smart pulley) DEVELOPERS OF LAB Kirk Reinhardt, JD738 Ted Brown, JD806 OVERVIEW OF LAB DESCRIPTION In this exercise students will experiment with a dynamics cart to determine the relationship between the applied force acting on the cart and its resultant motion. Students will be asked to devise procedures that will allow them to correctly predict the acceleration of a cart when a known force is applied. CURRICULUM CONSIDERATIONS This lab is intended as the introduction to Newton s Second Law. Students should have previously studied motion (specifically constant acceleration) and know how to represent motions using graphs of position, velocity and acceleration vs. time. Students should also have been introduced to the concept of force and its measurements. SAFETY CONSIDERATIONS: Students should be cautioned about allowing the cart to fall off the track or to collide with the smart pulley. BACKGROUND INFORMATION: A. SCIENTIFIC VIEWPOINT The underlying concept involved in this lab is Newton s Second Law (F = ma). Students should also know how to determine the acceleration of an object from its graph of velocity vs. time. B. COMMON MISCONCEPTIONS: 1.When a force is applied to an object, it produces motion in the direction of the force. 2.Under the influence of a constant force, the objects move with constant velocity. 3. The velocity of an object, is proportional to the magnitude of the applied force. 4. In the absence of a force, objects are either at rest or, if moving, are slowing down. OBJECTIVES: After completing the lab, students will be able to: 1.predict the acceleration of an object subjected to a single force. 2.Describe the motion of an object acted on by a constant force. 3.State the relationship among the variables force, mass and acceleration (F =ma)

2 EQUIPMENT/MATERIALS *Computer with PASCO 500/750 interface *mass set and hanger *smart pulley, clamp and string *cart and 1.2 m track spring scale reading in Newtons *surge protector *provided by SOTM ADVANCED PREPARATION: It would be helpful for the teacher to have assembled one set of apparatus and to have a way of displaying the software to the whole class. II. PRE-LAB PRE-LAB EXERCISE TO ELICIT STUDENTS PRIOR KNOWLEDGE AND MISCONCEPTIONS The teacher will set up and level the frictionless track with the cart. The teacher will give the cart with an initial push and have the students observe the motion of the cart. Ask the students to write answers to following questions: 1. What type of motion does the cart have? 2. What caused this type of motion? 3. Would the cart continue with this type of motion? 4. How would you graph displacement versus time? 5. How would you graph velocity versus time? DISCUSSION OF PRECONCEPTIONS When the students have completed this, discuss the responses to the first three questions as a class. Important points: The cart is moving with no force acting on it. The speed of the cart in nearly constant. If the idea of friction comes up in the discussion, note that the force acts in the opposite direction of velocity. Second, have different students put a few of the graphs on the board and discuss hese bringing out the misconceptions about uniform motion versus acceleration.(try not to use the word acceleration)

3 III. EXPLORATION OF SCIENTIFIC PRINCIPLE & INTRODUCTION OF EXPERIMENTAL PROTOCOL PROBLEM What will happen to motion of the cart if we apply a constant force at the end of the pulley? EXPERIMENT AND TECHNICAL OPERATION OF EQUIPMENT The teacher will run and describe the lab using the PASCO interface equipment and the smart pulley. The teacher will hook a small mass over the end of the pulley and let the cart move. Ask the following questions: What type of motion does the cart have? What caused this type of motion? Sketch the following graphs: Displacement versus time Velocity versus time. Using the PASCO and laptop, show the students the three graphs( d Vs t, v Vs t & a Vs t) Discuss these graphs and make sure equipment and graphs are clear. Cart Smart Pulley Clamp To interface Mass Newton s Second Law: Acceleration of a Cart (SP) IV. ELABORATION OF SCIENTIFIC PRINCIPLE: INQUIRY-BASED STUDENT INVESTIGATION PROBLEM What would happen to the motion of the cart if the amount of force applied increased? What would happen to the motion of the cart if the mass of the cart increased? HYPOTHESIS OR PREDICTION Could you predict the increase in velocity of the cart by knowing the force applied and the mass of the cart? EXPERIMENTAL DESIGN Can you list the variables that need to be considered. How can you change the variables you have identified to predict the acceleration of the cart?

4 Remember to change only one independent variable at a time when predicting the variable s effect on acceleration. Set up a procedure for your lab and call me over when you would like me to look at it. Checkpoint (Teacher checks students experimental design for feasibility.) tips: Check variables, how many remain constant or change?, Why they chose these? How this design will answer their specific problem? Check to see that both mass and force are being considered. Make sure that only one variable is being changed at a time. What data are the students collecting? PLAN FOR DATA COLLECTION & ANALYSIS When you are setting up your data collection, keep these points in mind. What kind of data will you need for your prediction? What graphs will you need based upon your variables? How will your graphs be able to show the relationship of your prediction? When you believe that you have a scheme for data collection, call me over. Checkpoint (Teacher checks students plan for feasibility.) tips: Check number of trials, what are their expectations for their data, and how will they manipulate their data ( i.e. y = m x + b for linear)? CONDUCTING THE EXPERIMENT Checkpoint (Teacher monitors students investigations in progress). ANALYSIS OF DATA Are students gathering data that will allow them to solve their problem? Are they using correct units for their various quantities? Are their graphs appropriate? Do they understand what the graphs represent physically? Checkpoint (Teacher checks students analysis.) DISCUSSION OF RESULTS COMPARE What factors did change the acceleration of the cart? Who was able to show their prediction? Are there any groups, whose data did not provide enough information to conclude their prediction? How do our prediction that were shown compare with our misconceptions? What misconceptions do we have confidence in dispelling? PERSUADE List predictions on the board that were shown by evidence in the lab. Have students list their reasoning from data why their prediction was shown. Come to a consensus on a prediction leading students to F=ma. (Hopefully already on the board in some form.) Have students in the class argue their point to other students for the correct prediction based on their reasoning. Can this lab lead to any further investigation about motion?(these might allow you to lead this to other labs or upcoming concepts) RELATE Have students come with ways in the real world that the direct relationship between force and acceleration is used. More examples: Launch of the Space Shuttle,Air bags, force to decelerate braking systems in vehicles, car on a curved road & roller coasters

5 V. EVALUATION POST-LAB SURVEY OF STUDENTS CONCEPTIONS Have students retake the Pre-Lab Exercise. Compare pre-lab and post-lab responses. TRADITIONAL Questions: A. A constant force of 0.50 N is applied to a cart with a mass of 600 g (0.6kg): 1. Sketch the following graphs for the motion that takes place. ( d Vs t, v Vs t & a Vs t) 2. What difference in the graph of v Vs t would be seen if a. the mass of the cart was larger? b. the applied force was larger? 3. a. What acceleration would the cart have? (show how you arrived at your answer) b. With your apparatus, measure the actual acceleration for the cart with a 600 g mass and applied force of 0.50 N and compare with your prediction in part a. ALTERNATIVE You may provide an alternative assessment of the content, skill, and attitudinal objectives for this lab with a scoring rubric. 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.