Title: Forces, Friction and Motion Introduction Today we will learn about how the force put on an object determines how it will move when there is no friction and when there is friction. 1. Click this link: http://phet.colorado.edu/en/simulation/forces-­‐and-­‐motion-­‐basics This is a screen shot of the website: 2. Click the button that says “Run Now”. It might take a few minutes to load. The screen will look like this: 3. All answers will be recorded on your own paper. Option 1 Explore the first three tabs (skip the acceleration tab) at the top of the webpage individually. Manipulate the variables for each (one at a time and then in different combinations) to clarify the concepts being tested. You will want to click on the boxes in the upper right hand corner to see what the quantitative results and vector forces of your experiments turn out to be. Once you understand what the simulation is trying to convey, write a 150 summary for each topic (tab) that includes the following: a definition of the concept; an explanation of the different parameters of the experiment; a conclusive statement(s) about the relationship(s) being investigated (there may be more than one variable demonstrated in each case). It should be clear from your summary that you understand the concept fairly well. Option 2 Follow the instructions below for each investigation. Label each section and answer all the questions that are in bold print on your own paper in complete sentences. You do not need to restate the question. Part 1: Explore a Tug of War How does changing opposing forces, weights and distance affect net force? 1. Place a person on each side of the rope. 2. Hit the “go” button. 3. Hit the “Return” button. Try it again with either the same amount of men on each side or a different amount of men on each side. 4. Hit the “Reset all” button. Click box next to “sum of forces” and “values,” continue putting men on each side. 5. Hit the “Return” button. 1. What are three combinations that result in a win? 2. What are two combinations where you get a tie on both sides? 3. If there were only one man pulling the cart, what would the sum of forces be? Part 2: Forces and Motion. How does applied force and friction affect the speed of an object? 1. Click the tab “Motion” 2. Check the boxes next to “ force, values, masses, and speed” 3. Place a 50kg box on the skateboard. 4. Type 200 in the box for force (200N). The screen should look like this: 5. Press the play button. Count to ten. Describe what happens in this scenario? (Look at the speedometer) 6. Repeat steps 4 and 5 with the refrigerator. Describe what happens in this scenario? (Be sure to look at the speedometer during the experiment) 7. Click the “Reset All” button. 8. Repeat steps 2-­‐4 using different objects and different applied forces. You can also use the people. Remember to only change one variable at a time. 9. What happens to the speed of the skateboard when different objects are added using the same force? 10. What happens to the speed of the skateboard when only the applied force is different? 11. Why do you think this happens? Come up with a rule for the affect mass has on the applied force. 12. Using the information you have collected in your investigations, try to come up with the value in kilograms for the Mystery Box and write your prediction here: ____________. Part 3 -­‐ Friction 1. Click the tab “Friction” 2. Check the boxes next to “ forces and speed” 3. Place the refrigerator on the screen. Type 500 in the box (500N). The screen should look like this: 4. What happened in this scenario? 5. Click the “Reset All” button. 6. Check the boxes next to “values and speed” 7. Place the refrigerator on the screen. Type 500 in the box (500N). Press the play button. 8. Slide the friction tab toward “None”. 9. What happens as you slide the fiction tab closer to “None”? 10. While the refrigerator is moving, slide the friction tab toward “Lots”. 11. What happens as you slide the fiction tab closer to “Lots”? 12. Play around with the “Friction” tab by experimenting with different amounts of force. Choose different objects to experiment with, as well. Try applying forces in both directions. Use the yellow box again and check off “Forces,” “Sum of Forces,” “Values,” “Masses,” and “Speed.” Adjust the “Friction” bar to see what happens when there is more friction or less friction. 13. What do you notice about the sum of forces? Come up with a rule for the sum of forces. 14. Compare data from all experiments and make a conclusive statement about how mass, friction, and speed affect force (be sure to address all three).