Teacher S Version for Activity 4A: Newton S Second Law Part 1
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Newton’s Second Law with the PASCO 750’s
Purpose What happens to an object when you apply a net force to it? What happens to the motion when you change the magnitude of that net force? What happens to the motion of an object if you change the mass of the object but keep the net force constant?
Materials Equipment Needed Equipment Needed 750, USB & power cord Braided Physics String Mass and Hanger Set Super Pulley with Clamp Dynamic cart and track Procedure
You can use the same equipment setup for both Part 1 and Part 2 of Newton's Second Law. Part 1 1. Plug the USB Link from the 750 into the computer’s USB port and plug in the power cord. 2. Open Data Studio and choose Create an Experiment 3. A picture of 750 will be on the screen. Click on the number 1. A list of probes will appear. Choose Motion Sensor. Note it will show the motion sensor with the cords in the order they must be plugged into port one and two (I believe it is yellow in 1 and black in 2) 4. Place the Motion Sensor on the end of the track closest to the computer. The other end of the track will be at the end of the table. 5. Attach the Pulley to the end of the track (near the edge of the table). If you have a piece of wood you can place this in front of the pulley to stop the cart. Of tape a piece of bunched up paper to the track (no tape on the track surface) 6. Level the track. 7. Attach a piece of string about 1.2 m long to one end of the cart. 8. Add a 20-g mass to the 5-g mass hanger. Record the mass. 9. Put two 20-g masses into the accessory tray on top of the cart. 10. Weigh the cart. 11. Attach the mass hanger to the other end of the string, and put the string in the pulley's groove. 12. Adjust the pulley up or down so the string is parallel to the track as shown in the diagram. 13. Hold the cart in front of the Motion Sensor but no closer than 15 cm from the sensor.
Note: Catch the cart before it hits the pulley or you could damage the pulley. 14. Click Start. Release the cart. Stop the cart before it hits the pulley and click Stop. 15. For Run #2, move a 20-g mass from the cart to the hanger Record data as outlined in step 14. 16. For Run #3, move the remaining 20-g mass from the cart to the hanger Record data as outlined in step 14.
Analysis 1. On the left side of the screen, Drag “Run 1” from the top data section onto “Graph” found in the Displays below. 2. Highlight the initial linear part of the graph. Choose Display from the menu and the pick “Scale”. 3. Click the Fit menu which is right above the graph (not up with the menu bar) and choose Linear.
The slope "m" of the best-fit line is the acceleration. 4. After recording the slope for Run #1, re-do the above for run 2 and 3.
This example shows the highlighted area and the Linear Fit information box.
Procedure Part 2 17. Add a 20-g mass to the mass hanger. 18. Click Start. Release the cart. Stop the cart before it hits the pulley and click Stop. 19. For Run #2, add 250-g of mass to the cart. Record the total mass of the cart plus the extra mass. Record data as before. 20. For Run #3, add a second 250-g mass to the cart. Record the total mass of the cart plus the extra mass. Record data as before.
Analysis Do the analysis exactly the same as in part 1. To put your graphs into your lab report: From the Menu bar choose “Display”/”export picture”. Save it to the desk top. Open it from the desktop and save it as either a jpg or bmp – this you can paste into Word. If you are a PC person, and you cut and paste the graph into your Word document today on the Mac, when you go home, it will not be visible. You must do it the following way: from the menu bar, choose “Insert”/”picture”/”from file” and find your file name. Otherwise, it saves your picture in a compressed format that PC’s cannot read.
Conclusion questions (answer for both part 1 and part 2) What variable(s) did you keep the same from one run to the next? What variable(s) did you control? How did this affect the acceleration of the cart?