### Hot Wheels Stopping Distance

Resource:
Science Reasoning Center: Hot Wheels Stopping Distance

Description:
This passage describes an experiment in which students release a Hot Wheels car from various locations along an inclined track and measure its speed at the bottom and the distance it slides upon hitting a box. Data is presented in the form of two figures and a data table. Questions target a student's ability to understand an experimental design, to identify the effect (both qualitatively and quantitatively) of one variable upon another variable, to combine information from two figures or a figure and a table to make predictions and draw conclusions, to extrapolate from data in a table or a figure, and to use provided data to evaluate a claim.

Performance Expectation:
HS-PS3-1  Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.

This activity aligns with the three dimensions of the Next Generation Science Standards in the manner described below:

Disciplinary Core Ideas
 Definitions of Energy (HS-PS3.A.1): Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system's total energy is conserved, even as, within the system, energy is continually transferred from one object to another and between its various forms. As students consider an experiment in which a car is released from different heights along an angled track, they determine that the greater the release height the greater the car’s speed at the bottom of the ramp.  Although not explicitly stated in the passage, this observation is clearly the result of energy conservation.  Furthermore, as each car hits a box and eventually comes to rest, students see that the greater the speed just before hitting the box the greater the distance the box is pushed.  And while these results are not surprising, the data is once again entirely consistent with the concept that the work done by friction in bringing the car to rest is equal to the initial kinetic energy of car.  Conservation of energy surfaces once again! Conservation of Energy and Energy Transfer  (HS-PS3.B.1):  Conservation of energy means that the total change of energy in any system is always equal to the total energy transferred into or out of the system. Students analyze the relationship between the stopping distance of the car and the intiial speed of the car prior to hitting the box. The relationship is based on the idea that the kinetic energy of the car is dissipated from the system as thermal energy. The work done upon the car is what causes this dissipated energy and the subsequent heating of the wheels and track.

Crosscutting Concepts
 ContentCause and Effect: Cause and effect relationships can be suggested and predicted for natural and designed systems by examining what is known about smaller-scale mechanisms within the system. At least two cause and effect relationships are suggested by students as they consider the questions at the close of this passage.  First, a greater release height causes a greater car speed at the bottom of the ramp.  Second, a greater speed at the bottom of the ramp causes the car to push the box a greater distance.  Each of these relationships suggests a transfer of energy that is once again entirely consistent with the principle of conservation of energy. Energy and Matter: Changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system. Although energy is not explicitly stated in this data presentation, this passage serves as a rich data presentation that clearly illustrates the conservation of energy.  As a car is lifted to a greater release height on the ramp, more energy is put into the car system.  Upon release, the car’s potential energy is transferred to kinetic energy as the car rolls downhill.  Finally, as the car collides with the box, frictional forces do work on the car and box as they lose kinetic energy and eventually come to rest.

Practices
 Analyzing and Interpreting Data:  Analyze data using computational models in order to make valid and reliable scientific claims. After carefully analyzing this passage and the data representations found here, students are asked to make several claims that come as a result of conservation of energy.   And while conservation of energy is an underlying principle in all the data presented, because it is not explicitly stated, students are able to uncover this important concept as the reason behind the results they find. Engaging in Argument from Evidence: Apply scientific principles and evidence to provide an explanation of phenomena and solve design problems, taking into account possible unanticipated effects. When students are presented with new situations in the last several questions at the close of this passage, they are required to use the evidence that they had previously uncovered to predict the results of a trial not yet performed.  In doing so, they are engaging in argument from evidence to provide a hypothesis for a new scenario. Using Mathematical and Computational Thinking: Use mathematical and/or computational representations of phenomena or design solutions to support explanations. The ability to use mathematical reasoning is an important skill for all science students. Questions 4 and 5 in this passage are examples of such reasoning where students are asked to predict the effect on one quantity (such as speed) when another quantity (such as release height) is doubled.  As not all relationships in physics are directly proportional, students must wrestle with the relationship that does exist between quantities and then apply this relationship to support an explanation.

Associated Reading from The Physics Classroom

Other Supporting Pages at The Physics Classroom:

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