Kate and Christopher use the Races applet to explore how to make the red car go slower than the blue car when both cars travel the same distance of 15 miles.
For use in a classroom, pause the video and ask these questions:
1. [Pause video at 1:08] Christopher says that the number of minutes is the “time it takes” — the time it takes for what?
2. [Pause video at 4:15] How can you tell that the red car is slower than the blue car? Come up to the video display and point to what you are looking at in the video.
Support students’ ability to build on an argument by asking students to attend to and build on Kate and Christopher’s argument:
1. Kate says [1:55] that whichever car takes longer is the slower car. Talk with your neighbor on how to build on her explanation. Be ready to share with the class.
2. Christopher says that changing the number of minutes to 6 will make the red car go the same speed as the blue car [4:55]. With your neighbor, write a conjecture for how to choose an amount of time to make the red car go slower than the blue car when they both travel the same distance. Be ready to share your conjecture with the class.