Grade Level: Middle School to Early High School; Type: Physical Science
To determine if the material and the tensile strength of different types of skateboard wheels significantly affects the friction co-efficient- and therefore the velocity- of a skateboarder.
- What effect does friction have on velocity?
- What is the molecular composition of urethane?
- In what types of products do you find urethane?
- What is acceleration?
- What is velocity?
- How do hardness and tensile strength affect rebound?
Skateboarding, as a sport, took off in earnest in the 1970’s. It is not a coincidence that this correlated with the invention of the urethane wheel- it gave riders much more control of the skateboard, and provided a much less bone-jarring ride.
The wheel has evolved into many different ‘species’ so to speak, over the last few decades. While the base material is the same- urethane- the wheel now comes in many different strengths, diameters and widths. There has been some standardization in the machining process used to create the wheels, though, and this standardization allows us to isolate single characteristics. ‘Hardness’ – basically how much the wheel squishes - is the variable we will try and isolate here, but this can be substituted with any other characteristic, depending on your interest.
You will obviously need a skateboard- it isn’t suggested that you attempt this project if you have never skateboarded before. Besides this, you will need at least to sets of wheels, with different hardness, but THE SAME diameter, in order to isolate hardness as a single variable. Another option is to choose wheels of the same hardness, but different diameters. You can isolate any variable you choose, as long as you choose only one.
Besides these, you will need a stopwatch, a section of road or pavement that has a slight incline and little or no traffic, measuring tape, and tools to switch wheels- a socket wrench will do the trick.
- Chose a stretch of road or concrete with little or no traffic
- Make sure the area has an incline enough so that while standing on the skateboard, you will start rolling without needing to push off the ground
- Measure off 50 meters (or 20 or 100- enough to get some speed, in a distance that makes the math easy.)
- Starting from 0 meters, allow the skateboarder to step on the skateboard. Once both feet touch the board, start the stopwatch.
- Time how long it takes to complete the track.
- Convert the speed into a figure in meters/second
- Do this at least ten times, so that you can get an average figure for all trials. The more data, the better.
- Switch out the wheels
- Repeat all of the steps for the second set of wheels. If you are using more than one set, do this for all wheels.
- Display your raw data in a chart form.
- After you have collected all data and computed averages, graph the data comparing each wheel. As you are doing average velocity and not adjusting as time progresses, it might be a good idea to use a bar graph rather than a line graph.
- Take photos, display the wheels used and set up an attractive display for the science fair!
Terms/Concepts: Velocity;Friction; Drag; Acceleration; Urethane and Polyurethane; Hardness; Tensile strength; Radius; Rebound