To share with the entire class:

• 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
• LEGO MINDSTORMS Education EV3 Software 1.2.1, free online, you have to register a LEGO account first; at https://www.lego.com/en-us/mindstorms/downloads/download-software
• computer, loaded with EV3 1.2.1 software
• 2 surfaces, each a distance of 10 feet: 1) a rough surface such as carpet or gym mats, 2) a smooth surface such as tile floor, linoleum or glass
• stopwatch
• various materials to serve as alternatives to rubber robot tires, such as tape, string, rubber bands
• Steps to Construct the Trailer
• Friction Force Pre-Assessment, one per person
• Friction Force Data Sheet, one per person
• Friction Force Post-Assessment one per student

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:

• LEGO MINDSTORMS NXT robot, such as the NXT Base Set
• LEGO MINDSTORMS Education NXT Software 2.1