Pull-Back Car
Study Group (3 to 5 ppl): Mr Kremer, Ms Moore, Tesla D. Dragon
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★★ Use video analysis to a) build a velocity graph and b) make a claim about an object experiencing constant acceleration.
CLAIM: When the toy car is pulled back just 10cm, it increases speed with an acceleration of 0.5m/s/s to the right, then decreases speed at 0.3m/s/s to the left.
EVIDENCE:
EVIDENCE:
Figure 1: This velocity-time graph shows the toy car increasing speed, then decreasing speed immediately afterward. Right is positive, and the car is moving to the right for the entire time interval shown.
Figure 1: This velocity-time graph shows the toy car increasing speed, then decreasing speed immediately afterward. Right is positive, and the car is moving to the right for the entire time interval shown.
Figure 2: We used a toy pick up truck, took video with our phone and loaded into Logger Pro for video analysis.
Figure 2: We used a toy pick up truck, took video with our phone and loaded into Logger Pro for video analysis.
REASONING:
REASONING:
We decided to analyze the video of the car pulled back just 10cm, because we wanted to see it speed up a bit, then run out of juice. We wanted to show both increasing and decreasing speed in the same video.
As shown in the graph in Figure 1, for the first 1.5s the car is increasing speed at a roughly constant acceleration of 0.5m/s/s. The uncertainty in the graph is significant, especially around t = 2.8s, where the acceleration changes briefly. This uncertainty could be because the car is more difficult to see as it's moving faster. At about 3.5s, the car's acceleration immediately changes to about -0.3m/s/s, but there was a lot of uncertainty for these points.
I can conclude that the speed of the car after t - 3.5s is decreasing, because the acceleration points left but the velocity of the car points right. This is probably because the spring inside the car is completely unwound, and there is some friction between the car and the table.
I find it interesting that the increase in speed had a greater magnitude of acceleration than the decrease in speed. I imagine that if we pulled the car back even more we would see an even greater magnitude of acceleration, but we would have to compare our results with another situation to see for sure.
Use the rubrics below to guide your own work:
Use the rubrics below to guide your own work:
SPOILER ALERT!
SPOILER ALERT!
Try assessing the work on your own before reading the example below...
Try assessing the work on your own before reading the example below...
Example Assessment:
Selecting Relevant Sources: 5-6 The graph and the motion map are both strong data, but the connection between the motion map and the graph could be clearer, and the limitations of the graph should be discussed.
Patterns and Relationships: 5 -6 Both trend lines are analyzed, and the analysis is valid. But uncertainty should be discussed in more detail, and the break in the pattern at 2.7s should at least be mentioned.
Argumentative Claim: 5-6 The main claim is clear, and two subclaims are made in the last paragraph, but these subclaims could be explored in greater detail, either by expanding the experiment or the discussion to include another layer of analysis.
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