ACCELERATION AND VELOCITY INVESTIGATION

Grade Level: 11th — 12th

TEKS addressed:

¤112.42. Integrated Physics and Chemistry - (c) Knowledge and skills.

(2) Scientific Processes. The student uses scientific inquiry methods during field and laboratory investigations. The student is expected to:

    1. Organize, analyze, evaluate, make inferences, and predict trends from data

(3) Scientific Processes. The student uses critical thinking and scientific problem solving to make informed decisions. The student is expected to:

    1. Express laws symbolically and employ mathematical proceduresÉto solve physical problems

Performance Objectives:

¤       Students will be able to observe and record data from an object moving at constant velocity.

¤       Students will be able to observe and record data from an object moving under constant acceleration.

¤       Students will be able to create, analyze, and interpret graphs of objects in linear motion.

Required materials:

¤       One bowling ball

¤       Track for the bowling ball (metal with a U-shaped cross section would work best)

¤       Video camera that records time (to the nearest second at least) on the video

¤       Meter stick to measure off lengths along the track

¤       TV (preferably with large screen) and VCR

¤       Overhead transparencies (one for each student)

Narrative:

The class will record on video a bowling ball moving at constant velocity, and then moving under constant acceleration. From the video they will take measurements of position at various times to make position vs. time graphs, from which they can create velocity vs. time graphs.

Engage:

Ask the students to come up with examples in everyday life of objects moving at constant velocity. What about examples of constant acceleration? Challenge them on details to make them support their answers. (What about curvature of the Earth? What about air resistance?)

Explore:                              

Set up the track so that it is level. Set up the video camera to record the movement of the bowling ball along the track all in one shot (without panning). Use the meter stick to clearly mark off equal lengths along the track (every decimeter should be sufficient; make sure the markings will be clearly visible on the video tape.) Set the bowling ball rolling along the track and record its motion (make sure it moves for several seconds).

Now play back the recorded motion on the TV, and tell the students they have to make a position vs. time graph and a velocity vs. time graph. They can get data off the TV by taping a transparency to the screen and using "pause" to trace positions and record times.

Now elevate one end of the track a few inches and place the bowling ball at the elevated end and letting it roll to the other end under the effects of gravity alone (donÕt give it a push). Adjust the height of the elevated end to make sure the travel time is several seconds. Again record its motion on video, and play it back to let the students take data. They should make position vs. time graphs, velocity vs. time graphs, and acceleration vs. time graphs.

Elaborate:

Lead a discussion of the results. Ask the students how they determined the velocities for the velocity vs. time graphs. Are these instantaneous velocities or average velocities? How do they determine what time corresponds to each velocity? Can we determine the velocity from a position vs. time graph? Can we determine acceleration from a position vs. time graph? From a velocity vs. time graph? What are the units of the slopes of the various graphs? What are the units of the areas under the various curves?

Evaluate:

Have the students turn in their data and graphs, along with a written explanation of their reasoning in determining velocity and acceleration for the velocity vs. time and acceleration vs. time graphs.