Purpose: The purpose of this lab will is to simulate a laboratory exercise using a program known as "Interactive Physics." Such simulations are becoming increasingly common, as they allow dynamic models to be constructed and the effects of individual parameters to be isolated--particularly where this would not be convenient when working with the mechanical system. Equipment: Computer, Interactive Physics Paper, Pencil Experiment: 1. On one of the laboratory computers, locate and open the program entitled Interactive Physics. 2. On the right hand side of the window a toolbar should be visible. Select the rectangle tool by clicking on it, and draw a long narrow rectangle. Make it as long as the window, and less than a cm wide. This will act as a floor. Place it near the bottom of the window. 3. Next select the anchor tool from the right hand side of the tool bar. Place it anywhere on the rectangle, and click to "anchor" the rectangle in place. Now the floor will not "fall" under the influence of gravity when you activate the program. 4. Select the circle tool (above the anchor). Draw a small circle and place near the upper left-hand side of the window. 5. Double click on the circle (or click rapidly two or three times) until the attributes window appears. In this window you can select x and y coordinates for the circle, as well as x and y velocity components for the initial velocity. Set x = -3.5, y = 1.5, 1 of 6
V x = 5, V y = 0. Also click on the rectangle, and set its y position to -1.5 m (so that the ball is 3 meters above the floor). 6. Click "Run" on the upper left. Observe where the ball strikes, and then reset the simulation (also in the upper left). Press "Run" again and observe where the ball strikes a second time. Note: If the ball doesn t bounce off the rectangle, you need to increase the width of the rectangle. 7. Now Measure the position where the ball struck the platform. To do this, simply move the cursor along the floor. The x position is read out in the lower left. Note: You may find it easier to measure if you step the simulation frame by frame (see the VCR-like arrows under Lower left-hand side of the window). Once the simulation has run once, it creates a movie that can be stepped through, frame by frame. 8. Under the World pull-down menu, select gravity. Make sure that Vertical gravity of 9.8 is selected. With the precision of measurements in this simulation, greater accuracy is not needed. 9. Calculate how far the ball should travel from basic relations in projectile motion. Note that you are given the height and the initial velocity in the x direction. Enter your results in Table 1. Calculate the percent difference with the value entered in Step 6. 10. Repeat the simulation, but this time, change the velocity components of the ball so that V x = V y = 5 m/s. Also change the y component of position to approximately -1.5, so that the ball is fired from the ground. Run the simulation and measure the distance the ball actually traveled. Enter your results in Table 2. Note: If you get a message about bodies overlapping, you will need to start the ball slightly above the rectangle--you can manually adjust its position by dragging it. 11. Calculate how far the ball should actually travel from basic relations in projectile motion, and the initial conditions in Step 8. Enter your results in Table 2, and calculate the percent difference from the measured value. Results: Write at least one paragraph describing the following: what you expected to learn about the lab (i.e. what was the reason for conducting the experiment?) your results, and what you learned from them Think of at least one other experiment might you perform to verify these results 2 of 6
Think of at least one new question or problem that could be answered with the physics you have learned in this laboratory, or be extrapolated from the ideas in this laboratory. 3 of 6
Clean-Up: Before you can leave the classroom, you must clean up your equipment, and have your instructor sign below. How you divide clean-up duties between lab members is up to you. Clean-up involves: Completely dismantling the experimental setup Removing tape from anything you put tape on Drying-off any wet equipment Putting away equipment in proper boxes (if applicable) Returning equipment to proper cabinets, or to the cart at the front of the room Throwing away pieces of string, paper, and other detritus (i.e. your water bottles) Shutting down the computer Anything else that needs to be done to return the room to its pristine, pre lab form. I certify that the equipment used by has been cleaned up. (student s name),. (instructor s name) (date) 4 of 6
Data Table for "Exploring Projectile Motion" Name: Date: Lab partners Table 1: horizontal projectile motion distance (from simulation) distance from calculation % difference Calculations for Table 1: Table 2: Projectile fired at a 45 degree angle distance (from simulation) distance from calculation % difference Calculations for Table 2: 5 of 6
Challenge question: At what initial velocity would an object fired from the ground at a 45 degree angle travel the same distance as an object fired horizontally from a height of 3 m above the ground? Calculate the answer, and then use the simulation to verify the result. Enter the results in table 3. Note: you might have to zoom out to see the result... Table 3: Equal Range Determination velocity from calculation distance from simulation-- when fired horizontally distance from simulation-- when fired at a 45 degree angle Calculations for Table 3: 6 of 6