Lab 4 Constant Acceleration by Drew Von Maluski

Transcription

1 Lab 4 Constant Acceleration by Drew Von Maluski Note: Please record all your data and answers on the data sheet. In this lab you will familiarize yourself with using the LoggerPro software, LabPro equipment, and track / cart. You will also explore constant acceleration and become familiar with graphing position vs. time, velocity vs. time, and acceleration vs. time for constant acceleration. Setup: 1. Place the track on top of your table and level it using a level. The track must be leveled so the cart does not roll down the track on its own. 2. From the small table remove the cart, weights, Labpro interface, and optical motion sensor. Place the cart on the track, stop it, and confirm that it does not roll on its own (confirm the track is level). 3. Connect the USB cable from the computer to the Labpro interface. Connect the power cable to the Labpro interface. Connect the motion detector to the Labpro interface. NOTE: The motion detector is connected to the Digital 1 port (if the connector does not fit, do NOT force it). 4. Attach the motion detector to the track end so that the black/white bars line up with the bars on the track. The bars on the cart also have to be in line with the bars on the track. 5. Have someone in your group log on to the computer. Open up LoggerPro (found in the start menu under the Vernier folder). You should see a blank experiment with a position vs. time graph. 6. In LoggerPro, click on the Experiment Menu > Setup Sensors > Show all Sensors. Click the box corresponding to the Digital 1 port, and add sensor > motion encoder cart. Confirm that when the cart is powered on and moved along the track, LoggerPro displays a position value that changes with position. Note: when not taking data please turn the cart off to save battery life. 7. In LoggerPro click on the Experiment Menu, and then click on Data Collection. Adjust the settings so that it runs for a reasonable length of time (20sec) and adjust the sampling rate to 20 samples per second. 8. LoggerPro should now display a position vs. time graph, and a velocity vs. time graph. If you want to view an acceleration vs. time graph you can click the vertical axis of one graph and change it to acceleration. 9. NOTE: Zero the cart when the cart is next to the sensor. You must do this every time before taking data. To do this click on the 0 icon to the left of the start button in LoggerPro. Part 0: Baby steps Place two shims under the track to prop up the 0cm end by 0.5in. Predict the motion of the cart down the ramp when the 0cm side is propped up. Please draw the predicted motion under the graphs in the position vs. time, velocity vs. time, and acceleration vs. time graphs. Once you have predicted the motion run the experiment in LoggerPro. Someone in the group holds the cart at the sensor and another person clicks the start button. Wait until LoggerPro starts collecting data before releasing the cart. When the experiment is running release the cart with 0 initial velocity! As the cart moves Logger Pro should record position and velocity data. Stop the cart before it rolls off the track and stop the experiment. Draw this motion in the graphs (only ever include the relevant motion, not the time before the cart began moving or after it was caught). Part 1: Rolling like the big boys, or how to give your cart an extra 25HP. (vtec just kicked in yo) Now put all 4 shims under the 0cm side of the track to prop it up 1in. Predict the motion of the cart when it is released down the track. Once you sketch your predictions run the experiment and graph the actual motion. 1

2 Part 2: Predict / Measure Acceleration down an inclined plane In this part we predict and measure the acceleration of the cart down the ramp. We need to measure the incline of the ramp. Measure the height of both ends of the track and use trig to determine the angle of incline. Ask if you are unsure. Note: the track has a ruler on it, so you know the length of the track. In class we found the acceleration of a mass moving down an incline (with no friction), a = g sinθ. Calculate the predicted acceleration of the cart moving down the ramp. Now we measure the acceleration down the track. Use LoggerPro to record the position and velocity of the cart down the incline. Perhaps the best way to get the value for average acceleration is to work off the velocity vs. time graph. Highlight the relevant motion by clicking and dragging in the velocity vs. time graph (highlight only the motion after the cart was released but before the cart was stopped). With this portion of the graph highlighted click on the Linear Fit icon. With the linear fit you can read off the acceleration because the slope of the velocity vs. time graph is the acceleration. Do this two more times and find the average acceleration. Is your predicted acceleration within 5% of the actual average acceleration? Part 3: Mass dependence on an inclined plane, or lack thereof hopefully. maybe In this part we will explore if adjusting the cart mass has an effect on its acceleration down the ramp. For each mass you will repeat the measurement 3 times to get an average acceleration. We are interested in the acceleration while the cart is rolling down the track. When adding weight to the cart make sure you place it in the middle of the cart each time. Does adding weight to the cart change its average acceleration by a noticeable amount? Should it? Part 4: Displacement from v vs. t graphs. The area under a velocity vs. time graph equals displacement. Let s see if our equipment agrees. Start the cart at the top of the sensor and have LoggerPro record velocity vs. time as the cart rolls down. Please remember to zero the cart position before collecting data. Stop the cart before it leaves the track. Note: You MUST wait for LoggerPro to start collecting data before you release the cart. Select the appropriate velocity data and click the integrate button to find the area. Record this value on the data sheet as d area. Using the ruler along the track, you can measure the displacement of the cart down the track. Please measure to the same part of the cart each time. Record this value as d measured. Do these two values agree within ±2cm? Part 5: Bridge to Engineering. Negative effect on power reduction. Speed is still increasing. Mr. Spock Now place all 4 shims under the other side of the track to prop up the 100cm side by 1in. With the cart started at the 100cm side predict the new motion. After you predict the motion run the experiment. Make sure you catch the cart before it hits the sensor!!! Part 6: And don't ask for any more warp 9 speeds, Mr. Spock. Our star drive is completely burned out. The only thing we have left is impulse power. --Scott With all 4 shims under the 100cm side predict the motion of the cart when you start the cart at the sensor and give it an initial push up the ramp (so the cart moves up the ramp and then down the ramp). After you predict the motion run the experiment and graph the data. Make sure you catch the cart before it hits the sensor!!! 2

3 Part 0: Lab 4 Data Sheet by Drew Von Maluski Part 1: 3

4 Part 2: θ = a prediction = a 1 = a 2 = a 3 = a avg-measured = Is your predicted acceleration within 5% of the actual average acceleration? Part 3: Mass added (g) A 1 A 2 A 3 A avg Does adding weight to the cart change its average acceleration by a noticeable amount? Should it? Part 4: d area = d measured = Do these two values agree within ±2cm? 4

5 Part 5: Part 6: 5