Author: Sandy Van Natta
The motion of battery powered cars is investigated as the cars move along a level surface. Time and distance data is collected and graphed for cars moving with one battery and cars moving with two batteries. The pattern of data from both cars produces straight lines with positive slopes on the graphs. Analysis of the lines on the graphs indicate that the cars were moving at a constant speed (velocity) and that the car with two batteries moved with a greater overall speed than the car with one battery. Distance and time data is also used to calculate the average speed of the cars. The average speeds are then compared to the slopes of the lines on the respective distance vs time graphs.
For Getting Ready:
For the Engagement:
For the Procedure:
Perform the demonstration in the Engagement section of the Student Activity sheet. Emphasize that motion needs both time and distance data in order to be described accurately. In order to determine distance, a reference point from which distances can be measured must be established.
The participants may say that the wind up toy is moving at changing speeds. However, if you wind up the toy and have the legs of the toy moving before it touches the flat surface, it will have little noticeable acceleration (speeding up) when it starts to move forward. Picking the toy back up off the surface before it seems to "wind down", eliminates any noticeable deceleration (slowing down) of the toy. What your participants will view is a toy moving forward at a fairly constant or steady rate. It is this steady rate that they will be investigating in the module.
Assessment: Encourage all participants to take part in the discussion. The evaluation here is informal.
Place your participants in groups of 7 and follow the procedure directions in the Student Activity.
In Part A: Ask the participants to describe the motion of the car in words as they first release it from the starting line and view its motion without running the stopwatches. You may also ask them if they think the car is moving fast or slow. The participants should say that the car is moving in a straight line at a steady speed. Most of the participants will describe the cars speed as slow. However this answer is relative and will depend somewhat on the type of battery car used for this activity.
After data has been collected and filled into the first data table, ask the participants if the times listed in column 5 are nearly the same, and if so, why? (The times should be nearly the same since the car is traveling at a constant speed. It traveled each 100 cm distance in about the same amount of time.)
In Part B: Ask if the participants think the car will move faster or slower with two batteries and why? Most if not all participants will say that the car will move faster since it has more energy or experiences a greater force.
In Part C: Ask participants to look at the average speeds they placed in column 6. Make sure they realize that these speeds are about the same since the speed of the car stays fairly constant over each 100 cm distance.
Assessment: Monitor the groups work and discussions. Make sure they are completing the data tables and constructing their graphs.
Both graphs show a vehicle moving at a steady rate. Use the information on both the data tables and the graphs to lead into a general discussion on motion. A detailed explanation of the science can be found in the Explanation section of the student activity sheet.
These points need to be covered in the group discussion.
Part A: When analyzing the graph, ask what characteristic of the graph tells the participants that the car is moving with a steady speed. The participants should say that the data points plot on the graph as nearly a straight line. This indicates that both time and distance are changing at a steady rate. Therefore, the car is moving with a constant speed.
Part B: After recording the data, participants should note that the car is moving faster because it is covering the same distances in shorter amounts of time. When the data is graphed from the second car, the slope of the line will be steeper than the line on the first graph.
In Part C: After calculating the average speed for the entire run using the formula vavg = d/t, ask participants to compare this value to the average speeds for each 100 cm distance. Participants should find that this value is nearly the same as the individual 100 cm speed values. This again indicates that the car was moving at a constant speed. If the numerical values for the average speed of the one battery and two battery cars are compared, the two battery car does have a faster average speed than the one battery car.
When the slopes of the lines are computed for both graphs and compared to the respective average speeds computed by the formula vavg = d/t, they should be found to be nearly the same. The slope is the numerical ratio between distance and time and has the units of cm/sec in this activity.
Assessment: Monitor the discussion. Ask participants to give examples from their own teaching experiences relating to the demonstration and understanding of the concept of constant speed their own classes.
If time allows, you may wish to have participants try one of the activities suggested in the Elaboration section of the Student Activity sheet such as running the battery car up an inclined plane or timing another object moving at a relatively constant velocity such as the wind-up toy.
However, make sure you allow time to have participants discuss how they would apply what they have just learned in their classrooms. Give time for participants to complete the lesson implementation sheet as a first step toward moving to classroom implementation.
Assessment: Check the lesson implementation plans for faithfulness to the lesson just experienced. If possible, visit the participants' classes for onsite assessment.
A teacher needs to convey the idea that motion of an object can be described by the objects position, direction, and speed, and that motion can be measured and represented on a graph. This activity is designed to aid in developing these idea. The participants first choose a reference point or location for their cars from which distances can be measured. Once this frame of reference has been established, a change in position in a given direction can be measured. This change in position is called displacement. When the amount of time elapsed during the displacement is recorded, the participants have enough information to calculate the average speed (velocity) of their observed car. They can also graph the motion of their cars and determine that the slope of the line on their graph is the same as the calculated average speed of their car.
Science as Inquiry:
Content Standard A: As a result of activities in grades 5 – 8, all students should develop:
Physical Science Standards:
Content Standard B: as a result of their activities in grades 5-8, all students should develop an understanding of:
NSES PROFESSIONAL DEVELOPMENT STANDARD A: Professional development for teachers of science requires learning essential science content through the perspectives and methods of inquiry.
NSES PROFESSIONAL DEVELOPMENT STANDARD B: Professional development for teachers of science requires integrating knowledge of science, learning, pedagogy, and students; it also requires applying that knowledge to science teaching.
If materials are prepared in advance, this activity should take about 90 minutes to complete.
Purchase the battery powered cars from any toy store or sciece supply catalog. An inexpensive toy ($5.00 to $10.00) usually works as well as a more expensive toy.
No special safety or disposal procedures are required.
Have each group suggest another activity which could be used to teach the basics of motion in their own classrooms.
See the Explanation section of the Student Activity sheet
Participants may wish to tie this activity into a discussion of forces. Since the battery car is moving at a relatively constant rate, balanced forces must be acting on the car. Participants may want to list some of the forces acting on the car such as the mechanical force exerted by the motor on the wheels, gravity, and friction.
Form the groups of teachers with diversity in mind. You may want to place participants with weaker physical science backgrounds in groups having participants with stronger backgrounds.
None available for this module
Physical science activities created for OSCI, summer 2005, in cooperation with Miami University, Center for Chemical Education OSCI Materials are still available at www.terrificscience.org/osci/physical but it is not known how much longer they will be on the web. The Motion of a Battery Powered Car activity is on pages 55 - 64.