Contributed by: Council of Chief State School Officers (CCSSO/SCASS)
Item Description:
This event asks the students to determine the average speed of a
toy car as it travels six different distances set up by the student.
Three trials are to be done for each distance. The only requirement
is the longest distance must be at least three times longer than
the shortest distance.
Question 1 asks the students to explain why their data may be
more accurate for long distances or for short distances. The question
is attempting to help the students see that in a very short distance
the accuracy of their measurements was limited by the short time
interval. If they had difficulty starting and stopping the stopwatch
over the specified distance they were actually measuring the instantaneous
speed rather than the average speed.
A good response will show the student can interpret the results
they obtained. The speed of the toy car should have been approximately
the same for the three trials at the longer distances than it was
at the shorter distances. The precision of their instruments may
also have limited their ability to measure the time over a very
short distance.
Question 2 asks the students to describe an experiment to determine
if cars that pass by the school are speeding. The question is really
asking them to apply the concept they learned and used in the experiment,
that the average speed of an object is the distance traveled divided
by the time it takes to travel this distance.
A good response will show the student can apply this concept to
an actual situation. The experiment should include measurement of
the distance between two points that the car will pass by and a
method to determine the time it takes to travel that distance.
Comment: Many students answered question 2 by stating a policeman
should use a radar gun to see which cars are speeding. To eliminate
this problem, the question could have begun with "You are given
a stop watch and a measuring tape."
Summary Table
Criterion
1


Long distance with or without explanation (Q1)
OR
short distances with explanation based on experiment (Q1) 
2


An experiment is described. (Q2) 
3


Experiment includes at least one of these: (Q2)
 time, distance, accuracy (repeated observations) 
4


Experiment includes time and distance (Q2) and
accuracy is understood (Q1 or Q2). 
Rubric:
Criterion 1:
It is stated that the data is more accurate for long distances with
or without an explanation.
OR
it is stated the data is more accurate for short distances with
an explanation that is based on problems with the experimental design.
(Q1) For example:
a. Short because the car spins and turns over long distances.
b. Short because the car didn't travel in a straight
line all the time.
The following do not meet this criterion:
a. Short because we could time it better.
b. Short because the car would slow down when it went
far.
Criterion 2:
An experiment of some type is described to determine if cars passing
the school are speeding. (Q2) For example:
a. Use a radar gun from the police.
b. Drive a car by at 25 mph and see how many cars pass
it.
Criterion 3:
The experiment includes at least one of the following: (question
2)
A. The experiment includes measurement of time.
B. The experiment includes setting up a distance
to observe the cars traveling by the school.
C. The student recognizes that to achieve more accurate
results the experiment should be repeated (more than one car must
be observed).
Criterion 4:
Both of the following are met (from criteria 3):
A. The experiment includes measurement of time
(question 2).
B. The experiment includes setting up a distance
to observe the cars traveling by the school (question 2).
AND
C. The student recognizes that to achieve more accurate
results the experiment should be repeated (more than one car must
be observed. (question 2).
OR
D. The student stated and explained in question 1 why
longer distances increased the accuracy of their experiment.
For example:
a. There is more room if you make an error if you use
a longer distance.
b. The watch we used only could measure in seconds and
for some short distances it looked like 1.5 seconds. So the data
is more accurate for long distances (or any response that addresses
precision of the measurement tools).
