History & Physics of Skateboarding

Early Origins: Scooters Crate Scooters Began 1920s Used roller skate wheels Little to no ability to turn Wood box or crate with handle

Early Origins Other Modifications of standard roller skates – with metal wheels Similar to a dolly

Skateboarding Demographics 2002: 18 million skateboarders worldwide 85% under the age of 18 74% Male

Parts of a Skateboard Wheels/Bearings Trucks (base plate & Cushions) Deck (grip tape) Accessories (rail guard, nose guard, tail guard)

The Truck

The Wheel

Popularity Skateboarding popularity has waxed and waned over the last several decades. Popular: Late 1970s-mid 1980s Not Popular: Late 1980s to mid 1990s Popular : Late 1990s to 2003 Popularity Related to: Technologically changes in the board, cultural changes, and inventiveness of riding

History – Timeline of the Skateboard 1940s -1958: Southern California – Winter time surfers want to practice and created Skateboards. 1960s Clay Wheels 1973: Steerable truck Fiberglass, plastic & aluminum decks 1973: First Polyurethane wheel (open ball bearings) 1976: First Skate parks (200 skate parks by 1982) California drought –empty pools 1978: Sealed ball bearings 1979: Grip tape 1980s: Laminated wood for decks

History – Timeline of the Skateboard – The Moves 1950s: Street and sidewalk riding - practice surfing 1965: First Skateboard Competition 1970s: Freestyle & Street Slalom 1976: first skateboard parks 1977-1984: The First Vertical Revolution 1985: Age of the half -pipe 1992: 2nd Street Revolution 1995: The Second Vertical Revolution .

History – The Pioneers Alan Gelfan Tony Alva Mike Mcgill Rodney Mullen Steve Caballero Tony Hawk

The 1980’s Skaters made their own wooden ramps in their backyards to skate on. Street skating became more popular also. The Ollie: 80% Street tricks 60% Vertical tricks

1990’s The X-Games came out in the 1990s and made skateboarding even more popular. Large media coverage on skateboarding has moved it from an Skate parks have also gave boost to the skating community in many towns. The many different ramps, pipes and bowls present at these parks have led to a change in equipment.

Modern Types of Skateboards Street: (small, hard wheels & small decks) The wheel sizes are relatively small so that the boards are lighter, and the wheel's inertia is overcome quicker, thus making tricks more manageable. Vertical: Downhill: hard, large wheels, long decks Luge:

Forces of Skateboarding Use of forces: gravity, friction, momentum, rotational, and more – to complete a variety of moves Gravity: Gives speed to the skater – related to slope Friction: used by wheels to grip, grip tape to help hold rider to board, bearings lower friction in the wheels to increase speed

Forces of Skateboarding Momentum: Linear Momentum allows riders to reach a high vertical height – Height increased by thrusting. Flat part of a half-pipe allows for thrusting Momentum: Rotational aka Angular Momentum. Control allows to complete of a variety of moves.

Physics of some moves The 360 Angular momentum is conserved by controlling the arms – pulling them in makes you go faster.

Physics of some moves Vertical Vertical riding is maintained by centrifugal force. Rider stays vertical due to the circular motion imparted on rider/board. “g-forces” both positive and negative are experience by the rider. Heavy during vertical – weightless during the “air” portion of the ride.

Physics of some moves The Ollie Distribution of weight quickly changes from the back of the board to the front. Rebound (Newton’s Third Law) helps board and rider achieve altitude

Physics of some moves Luge & Downhill Riding Large wheels – good for speed High quality bearings for speed Hardness of wheel varies Decrease cross-sectional area to decrease air resistance. (ex. Luge – completely laying down.

The Ollie -Flat Press downward on front foot Release front foot as the back foot kicks down. Front foot controls the board through a parabolic path First done by Rodney Mullen

Downhill Nightmares Wobbles caused by resonance Resonance – the positive feedback loop of over compensation. Loss of balance Too much speed for a turn Gravel/rock: sudden impact

Videos http://www.youtube.com/watch?v=gwKCnk5y0gk http://www.youtube.com/watch?v=aexsHFhBT48 http://www.exploratorium.edu/skateboarding/trick.html http://www.youtube.com/watch?v=1CUWOCAiNc8