To share with the entire class:

• 2 LEGO MINDSTORMS EV3 robots (instructions to build and program basic robots are included with LEGO EV3 kits); LEGO MINDSTORMS EV3 robot, such as EV3 Core Set (5003400) at https://education.lego.com/en-us/products/lego-mindstorms-education-ev3-core-set/5003400#lego-mindstorms-education-ev3
• 2 pieces of a brightly colored yarn, each ~1.5 feet (.5 m) in length
• 2 pieces of a brightly colored yarn, each ~6 feet (2 m) in length
• chalk or dry erase marker to use with the classroom board
• Pre-Activity Quiz, one per student
• Post-Activity Quiz, one per student

Alternative: LEGO MINDSTORMS NXT Set:

Note: This activity can also be conducted with the older (and no longer sold) LEGO MINDSTORMS NXT set instead of EV3; see below for those supplies:

• 2 LEGO MINDSTORMS NXT robots

Note: As an alternative to using the LEGO robots, provide much longer lengths of yarn and have students walk along the two tracks to see if they "collide" with each other. Make it a fun "game," by dividing the class into teams with a representative from each team acting out each track scenario. Then give teams some time to quietly discuss the answers to the questions posed in the Procedure section before coming back together as a class. Then, call on teams to share their answers to the questions and see which teams got them right.