Roller derby is a physical sport that involves skating in a track and scoring points by passing other players. Each team has blockers trying to stop the other team's jammer from passing, while the jammer scores points for their team. The basics of motion in roller derby involve a low stance and using edges of the wheels for power and turns. Different surfaces impact friction and the type of wheels used. Momentum is transferred through hits using parts of the body. Injuries can occur from falls or hits at high speeds.

1. Rock-it Science: The
Physics of Roller Derby
Megan K. Pickett
(Deviled Meg, #1701)
Lawrence University
University of Washington
Jet City Roller Girls
Women’s Flat Track Derby Association

2. The Basics of Roller Derby
Rule 1.3.2: The team with the most points at the end of the game
wins.
Watch your Rose City Rollers Defend their Championship here in
Portland Nov 4-6!

3. The Basics of Roller Derby
Tends to be a bit physical.

4. The Basics of Roller Derby
Tends to be a bit physical.

5. Two Jammers:
Jammers score a
point for every
opposing player’s
hip they pass
(legally) once they
get out of the pack
for the first time.
Oh, yeah…

6. Each team has 4 blockers that make your life
miserable

7. Unless you make it miserable for them
Evil Jammer Nice Jammer
Nice Blockers
Nice Blocker
Evil Blocker
(Loredai KillMore)
(Lotta Issues)
(Banana Ramya)
(LuLu Palooza)

9. WTF?

11. Huzzah!
Lead
Jammer

12. My Work
Here is
Done

16. Basic Motion
“Derby Stance”

17. Basic Motion: The Cross Over

18. Basic Motion: The Cross Over
Power and speed
by pushing to the side.
Friction from the wheel
edges = power. Non-
pushing wheels provide
roll.
Turns body toward
center track—falling
around the circle

19. Navigating the Track
148.5 feet on the inside
236.5 feet on the outside.
Every skater must be able
to complete 27 laps/5
minutes = 12 mph
Jammers ~ 33+ = 15 mph
(Fc~400 N ~ 2/3 W)

21. Speaking of Friction: Best Friend and Worst Enemy
Wheels, Cushions, Toe Stops are given “durometer ratings”
20A = rubber band
40A = pencil eraser
70A = Running shoe sole
78A = Outdoor wheels
88A—95A = lighter skaters*
95—101A = heavier skaters*
(100ish = shopping cart wheel)

22. Speaking of Friction: Best Friend and Worst Enemy
…But surface conditions means different wheels (potentially)
for every venue...
Wooden Floor—”grippy”
Sport Court—ranges from grippy to slick with bumps
Painted Cement—grippy to slippery
Hockey floor—slippery
Masonite—I hate you
Why? Friction is a contact force. Does it matter? Sorta.

23. Slippery floor
Excellent for most stops: snow plows, hockey stops, power
slides, T-stops

24. Grippy floor
Excellent for turnaround toe-stops

25. …and general Jammer fun

26. Static, Kinetic, and Rolling Friction

27. Static, Kinetic, and Rolling Friction
Rolling Friction = Drag Force
Additional Dissipation due to
wheel deformation, bearings,
flex in trucks/plates/kingpins
F = CrrN.
=> Torque. Hence the different
wheels. Best estimates are
around Crr ~ 0.01

28. Static, Kinetic, and Rolling Friction
Wheels! Big Wheels,
Little Wheels, Wide,
narrow, cores, urethane
pours.
I = MR2 for each wheel.

29. Momentum Transfer: The Whip
Arm Whips, Hip Whips,
Shirt Whips, Legging
Whips, Leg Whips. All
Newton, All the Time

30. Momentum Transfer: The Whip
Arm Whips, Hip Whips,
Shirt Whips, Legging
Whips, Leg Whips. All
Newton, All the Time

31. Overtime
400,000 N/m2 to break a human femur (not difficult at
15 mph with a 100 kg blocker falling on you.
Concussion rate: 10% players 3+ concussions (average
playing time before a concussion is 3.5 years
League Bacterial Flora

32. Overtime