- Computers are needed for lab this week
- Video Analysis using Logger Pro:
Measure the initial kinetic energy, and final potential energy of a ball dropped vertically
- Why aren't we doing an actual experiment? Energy is conserved when only conservative forces (e.g. gravity) act on the system. Non-conservative forces (e.g. friction) cause a lot of problems. In the past, we've done three different conservation of energy experiments, and none have consistently shown that energy is conserved!
- Data uncertainty: The image of the ball gets blurry near the end of the video as the velocity increases, resulting in error in marking the true position of the ball. Need a better video!
- Remind students to "undo" immediately if they plot a point in the wrong position. It can't be corrected later!
- Here's a scan of my results, with associated calculations of acceleration and energy. Students are now told to use the point closest to t = 0.2 s, which should be point #13
- Graph: If the total energy curve closely follows the potential energy curve, have students check the frame rate under Movie options (see step 5 in the Experiment section of the instructions). The frame rate is likely incorrect; it should be 60 fps. Correcting this setting fixes the graph
- Biggest difficulties?
- They can't follow directions
- Lack of fine motor skills
- Small screen laptops? My results for g (961 cm/s2, 2% low) were created on a large screen display. Students using our laptops will typically get around 900 to 940 cm/s2
- Historical note: This procedure may no longer be necessary, but computer behavior varies from year to year, so who knows? The screen brightness needs to be turned up when running the laptops on battery power; it's difficult to mark points precisely when the screen is dim. Frequently, the function keys for screen brightness didn't work. The following steps to increase screen brightness will be written on the board:
- Right-click on desktop
- Choose Display Settings
- Drag Adjust Brightness Level slider all the way to the right
|
