1 Speed and Gravitational Force Lesson Created by Carlos Irizarry, George B. Swift Specialty School (CPS), Chicago, Illinois Purpose The concepts of speed, acceleration, and gravitational energy are a few of the most fundamental principles of physical science. For most students, exploration of these dynamics is the beginning of their understanding of the greater world of physics. Much of their future success in this field is determined by the students ability to grasp the relationships between forces and their effects, such as the relationship between an object s speed, acceleration, and the gravitational forced acted upon it. Overview Students will use a toy car, track, and ramp to measure the amount of time it takes the car to travel 1 meter when released from different heights on the ramp. Through free experimentation, students should grasp the relationships between height, incline, starting position, and gravitational force. Using the photo gate, students are able to obtain very accurate data sets which they will then organize and present in graph and table form. Student Outcomes Illinois State Standards: 12.D.3a: Explain and demonstrate how forces affect motion. 12.D.3b: Explain the factors that affect the gravitational forces on objects (e.g., changes in mass, distance). National Science Education Standards: 8ASI1.3: Use appropriate tools and techniques to gather, analyze, and interpret data. The use of tools and techniques, including mathematics, will be guided by the question asked and the investigations students design. The use of computers for the collection, summary, and display of evidence is part of this standard. Students should be able to access, gather, store, retrieve, and organize data, using hardware and software designed for these purposes. 8ASI2.1: Different kinds of questions suggest different kinds of scientific investigations. Some investigations involve observing and describing objects, organisms, or events; some involve collecting specimens; some involve experiments; some involve seeking more information; some involve discovery of new objects and phenomena; and some involve making models. 8ASI2.4: Technology used to gather data enhances accuracy and allows scientists to analyze and quantify results of investigations. Speed & Gravitational Force - - Teacher Overview - - 3 pages
2 8BPS2.1: The motion of an object can be described by its position, direction of motion, and speed. That motion can be measured and represented on a graph. Time This activity can cover the span of two class periods (45 min. each) with the first period being dedicated to experimentation and data gathering. The second period may be spent interpreting and formally publishing data sets through graphs and tables. Level 8 th grade Physical Science Materials and Tools (for each student group) HP tablet computer HP 39gs graphing calculator emulator software Fourier photo gate sensor (DT137) HP StreamSmart 400 2 track pieces 1 cart (toy car) 1 ramp Masking tape meter stick Preparation Test all photo gates and HP tablets and make certain they are operational. Ensure that there are enough materials available to students to support student autonomy. Prerequisites This activity is best used just after students have grasped a working understanding of Speed, Acceleration, and Gravitational Force. Students must understand that these are separate, although related, concepts. Background Students should also be well trained in using the photo gate and gathering data on the HP tablets. Students should also have considerable experience in transferring data to graph and table form. Experience in formally publishing data is needed. Speed & Gravitational Force - - Teacher Overview - - 3 pages
Teaching Notes For this activity, any other free rolling object may be used in lieu of the toy car. A toy car race set may be used for the activity but any other controlled ramp and path apparatus can suffice. This activity can also be done on a larger scale using a skateboard and skate ramp, although it may make using the photo gate difficult. 3 This work is supported by a grant from Hewlett- Packard under the HP Catalyst Initiative. However, any opinions, findings, conclusions and/or recommendations are those of the investigators and do not necessarily reflect the views of the funders. Speed & Gravitational Force - - Teacher Overview - - 3 pages
1 Review: Speed and Gravitational Force Speed is the measure of how much distance is covered within a certain amount of time. The simple formula used is Speed = Distance/Time. Remember that while we may be most familiar with measuring speed in miles per hour, sometimes we need to measure in smaller units of distance and time as needed. Look at the teacher s track and ramp setup. With which units do you think we ll be using? Kilometers and hours? Centimeters and seconds? Remember that Gravitational Potential Energy is the energy an object possesses because of its position relative to the earth. We learned that the amount of work used to place the object in its position (Weight) is multiplied by the distance the object moves/falls (Height). Gravitational Potential Energy = Weight x Height. Would you rather trip and fall down one stair or trip and fall over the side of a two- story building? Why? From which would you have greater G.P.E. before beginning the fall? Challenge: Using the photo gate sensors, your group will record the time it takes a cart to travel 100cm. You will conduct 15 timed trials, five at each of the three pre- set starting points of the ramp. Each starting point will be at a different height. Think aloud with your group Does a marble move faster across the floor if pushed with more force? Which is more exciting when sledding, the low hill or the high hill? Why? Procedure: 1. In your science notebook, make a table like the one below. 2. Set up your ramp and track just like the teacher setup on display. 3. Measure out and label 100cm from each starting point along the ramp. Understand that you will have three finish lines because you have three different starting points. 4. Assign your group members the roles of cart releaser, data recorder, sensor expert, and quality control manager. Be sure to swap jobs as needed throughout the activity! Speed & Gravitational Force Student Guide 2 pages
2 5. Setup your photo gate sensors with their ring stands. One should be placed at starting point A and the second photo gate sensor should be placed at the corresponding finish line. 6. Hold the cart so that its front end is just before starting point A (before the photo gate). 7. Release the cart and observe. 8. The sensor expert should share the time elapsed from when the cart passed through the first photo gate to when it passed through the second photo gate. 9. Repeat steps 6-8 four more times for a total of five trials with starting point A. 10. Repeat steps 6-9 for starting point B. 11. Predict and discuss with your group: What kind of results can you expect from the trials using starting point C? Why do you think so? Record your group s thoughts and predictions in your science notebook. 12. Repeats steps 6-9 for starting point C. Analysis How did the starting position height of the cart affect the speed of the cart? From which starting point do you think the cart had the most force? How does the photo gate help improve accuracy? Why is human error a large problem for scientists when conducting trials? What real world experiences seem to coincide with our findings? Data Table Template: Cart Starting Position Point A (Highest) Point B Speed Traveled (cm/s) Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Average Speed (cm/s) Point C (Lowest) Speed & Gravitational Force Student Guide 2 pages