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A gravity racer or soapbox is a motorless vehicle which is raced on a downhill road either against the clock or against another competitor. Although most are built for the purpose of recreation, some gravity racing teams take the sport more seriously and compete to win. They are propelled by
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
and can achieve speeds upwards of 164 km/h (101 mph).


Soapbox cars

Originally, gravity racer cars were built from wooden soap (or apple) crates and rollerskate wheels, but have grown more sophisticated over time, with materials like
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
,
fiberglass Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cloth ...
and even
CFRP CFRP may refer to: * Carbon fiber reinforced polymer Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, ...
being used. In the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
a gravity racer car has been called a buggy, trolley, cart. It is currently popularly called a soapbox. In Scotland and northern England it has also been called a bogie, cartie/cairtie, guider or piler. In Wales it is often referred to as a gambo. In Australia they are called billy-carts, and in Brazil it is known as rolimã. In addition to being built by children, there are organised competitions and races ("soapbox or billycart derby") that often engage the enthusiasm of adults. However, these are usually entered into in a spirit of fun rather than serious competition. Often they will be fund-raisers for
charity Charity may refer to: Giving * Charitable organization or charity, a non-profit organization whose primary objectives are philanthropy and social well-being of persons * Charity (practice), the practice of being benevolent, giving and sharing * Ch ...
. Many, but not all, events impose the following rules: *The car must have no
motor An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...
*The car must have at least 4
wheel A wheel is a circular component that is intended to rotate on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the wheel and axle which is one of the Simple machine, six simple machines. Wheels, in conjunction wi ...
s *The car may have to have some type of
brake A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background ...
s *The driver must wear a
helmet A helmet is a form of protective gear worn to protect the head. More specifically, a helmet complements the skull in protecting the human brain. Ceremonial or symbolic helmets (e.g., a policeman's helmet in the United Kingdom) without protect ...
*A push at the top is allowed for speed Soapbox cars weigh an average of and reach top speeds of . Many cities have permanent tracks where drivers compete for prizes.


Construction

A typical gravity racer cart is usually made of
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
, and has 4
wheel A wheel is a circular component that is intended to rotate on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the wheel and axle which is one of the Simple machine, six simple machines. Wheels, in conjunction wi ...
s, arranged as a fixed rear
axle An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearing ...
, and a steerable front beam axle - usually with a very simple single central
pivot Pivot may refer to: *Pivot, the point of rotation in a lever system *More generally, the center point of any rotational system *Pivot joint, a kind of joint between bones in the body *Pivot turn, a dance move Companies *Incitec Pivot, an Austra ...
. A seat is arranged at the back, and perhaps the seat area is enclosed, as in the original soap-box design. More sophisticated designs might employ a fully enclosed body. The types of wheels employed vary according to what can be obtained easily - wheels from baby carriages, pushchairs, prams, and discarded
bicycle A bicycle, also called a pedal cycle, bike or cycle, is a human-powered or motor-powered assisted, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A is called a cyclist, or bicyclist. Bic ...
s being common. Ready-made wheels are also available from hardware suppliers. Steering is typically actuated using a rope connected to the ends of the steerable beam (which can then double as a useful manual pulling device). More sophisticated steering methods are sometimes seen.
Brake A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background ...
s are also commonly used, and most soap-box cart racing contests require these. Often a simple friction brake operated by a lever which bears on one of the tyres is all that is required under the rules. Gravity racer carts are unpowered, and are either pushed by willing helpers, or are run down a suitable slope. Races will usually take place downhill and the most efficient and skillfully driven cart will win -
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
applying equally to all. Gravity racer carts also make great construction projects for children, requiring only an intuitive sense of
engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad rang ...
, and a few basic construction skills. There are also predesigned kits available, though for many this defeats the purpose of the exercise. Recently, more advanced gravity racers are beginning to emerge. These, intended for competition in the major soapbox races, are sometimes made of
carbon fibre Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
and feature a
monocoque Monocoque ( ), also called structural skin, is a structural system in which loads are supported by an object's external skin, in a manner similar to an egg shell. The word ''monocoque'' is a French term for "single shell". First used for boats, ...
design, although most use a more traditional
chassis A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of an artificial object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpart ...
or
spaceframe In architecture and structural engineering, a space frame or space structure ( 3D truss) is a rigid, lightweight, truss-like structure constructed from interlocking struts in a geometric pattern. Space frames can be used to span large areas with ...
design with bodywork made from materials such as
plywood Plywood is a material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another. It is an engineered wood from the family of manufactured ...
,
corrugated plastic Corrugated plastic or corriboard – also known under the tradenames of Cartonplast, Polyflute, Coroplast, FlutePlast, IntePro, Proplex, Correx, Twinplast, Corriflute or Corflute – refers to a wide range of extruded twinwall plastic-sheet prod ...
or similar. Examples of such soapboxes include the
Lotus 119c Lotus 119 was a box car built by Lotus Cars to compete at the Soapbox Challenge that took place at the 2002 Goodwood Festival of Speed. It is believed to be the fastest box car built, capable of 200 mph (320 km/h) on a 45 degree slope. Several ...
and the
Formula Gravity VXR Nimbus In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
. In Australia billy carts tend to conform, even in the 21st century, to a more traditional or rudimentary specification often being constructed informally by juveniles from found or inexpensive materials with minimal adult input and used without safety equipment. However even when construction of vehicles is more formally organised, such as for the annual Blacktown and District Cub Scout Billy Cart Derby at Rooty Hill, NSW the vehicle is still constructed to a deliberately relatively unsophisticated design, although safety is a consideration. In Indonesia, billy carts are also known as 'gokar'. They are raced in different regions as a community social activity. The form of the cart is similar to the Australian one. However, the wheels are often motor cycle wheel bearings. In
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
, gravity racers are known as "carrinhos de rolimã." Traditional designs are very minimalistic, with an open board-like body and wheels made up of naked
ball bearings A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this ...
(no tyres allowed), usually discarded parts obtained from auto mechanics. Electric soapboxes are a new development and are not, in fact, pure gravity racers since they are electrically powered.


History of gravity racer races

The first recorded gravity race took place in 1904 in
Oberursel (Taunus) Oberursel (Taunus) () is a town in Germany and part of the Frankfurt Rhein-Main urban area. It is located to the north west of Frankfurt, in the Hochtaunuskreis county. It is the 13th largest town in Hesse. In 2011, the town hosted the 51st Hes ...
near
Frankfurt Frankfurt, officially Frankfurt am Main (; Hessian: , "Frank ford on the Main"), is the most populous city in the German state of Hesse. Its 791,000 inhabitants as of 2022 make it the fifth-most populous city in Germany. Located on its na ...
, Germany. It was inspired by major motor sports events like the Gordon Bennett Cup and the
Kaiserpreis The Kaiserpreis (german: Emperor's Prize) auto race, named after Emperor Wilhelm II, was held in 1907. Like his brother's Prinz-Heinrich-Fahrt held from 1908 to 1911, it was a precursor to the German Grand Prix. As Camille Jenatzy had won the Gordo ...
race. In 1933, ''Dayton Daily News'' newspaper photographer Myron Scott of
Dayton Dayton () is the sixth-largest city in the U.S. state of Ohio and the county seat of Montgomery County. A small part of the city extends into Greene County. The 2020 U.S. census estimate put the city population at 137,644, while Greater Da ...
,
Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...
had covered a race of boy-built cars in his home community and was so taken with the idea that he acquired rights to the event; the national-scale
Soap Box Derby The Soap Box Derby is a youth soapbox car racing program which has been run in the United States since 1933. World Championship finals are held each July at Derby Downs in Akron, Ohio. Cars competing in this and related events are unpowered, ...
grew out of this idea. In 1934, Scott had managed to persuade fifty cities across the United States to hold soap box car races and send a champion each to Dayton for a major race, later held in
Akron Akron () is the fifth-largest city in the U.S. state of Ohio and is the county seat of Summit County. It is located on the western edge of the Glaciated Allegheny Plateau, about south of downtown Cleveland. As of the 2020 Census, the city prop ...
. Scott later went on to work for
Chevrolet Chevrolet ( ), colloquially referred to as Chevy and formally the Chevrolet Motor Division of General Motors Company, is an American automobile division of the American manufacturer General Motors (GM). Louis Chevrolet (1878–1941) and ous ...
. In the UK, gravity racer derbies have recently become more popular, brought to the masses by large events such as the Red Bull Soapbox Race and that held between 2000 and 2004 at the
Goodwood Festival of Speed The Goodwood Festival of Speed is an annual motorsports festival featuring modern and historic motor racing vehicles taking part in a hillclimbing, hill climb and other events, held in the grounds of Goodwood House, West Sussex, England, in l ...
. Now, many small hilly communities organize their own races, such as the Catterline Cartie Challenge in Scotland and the Belchford Downhill Challenge in Lincolnshire, and there are now several dozen known races across the UK. An annual Soap Box Derby has taken place in mid-July at
Richard's Castle Richard's Castle is a village, castle and two civil parishes on the border of the counties of Herefordshire and Shropshire in England. The Herefordshire section of the parish had a population of 250 at the 2011 Census. The Shropshire section ...
on the Shropshire/Herefordshire border since 2004. In addition to the local community races, there are a small number of races which attract more serious competitors, such as Cairngorm Soapbox Extreme (held at
Cairn Gorm Cairn Gorm ( gd, An Càrn Gorm) is a mountain in the Scottish Highlands. It is part of the Cairngorms range and wider Grampian Mountains. With a summit elevation of above sea level, Cairn Gorm is classed as a Munro and is the seventh-h ...
from 2009 to 2012) and the Worlaby Downhill Challenge. These races tend to produce higher speeds than the community races. Gravity racers taking part in Cairngorm Soapbox Extreme in 2011 reached speeds of 70 mph.


Physics considerations

A gravity racer obtains its energy solely from the force of gravity (assuming no starting push is permitted), which is effectively equal for any combination of racer design and course. However, performance can be greatly affected by the combined effects of various forms of drag and also the moment of inertia of the wheels, and also of course by the skill of the driver in choosing optimal lines. Drag breaks down into
aerodynamic drag In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fl ...
and
rolling resistance Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. It is mainly caused by non-elastic effects; that is, not all the energy nee ...
. The latter can be minimised by careful attention to the wheel bearings, tyre sizes and pressures, and brakes (to avoid parasitic brake drag). High tyre pressures and narrower tyres will typically lower the tyre contact rolling resistance, usually at the expense of grip. Larger wheels have lower rolling resistance than small ones, and rolling resistance is also proportional to overall weight. If permitted, a 3-wheeler design will have 25% less rotational inertia than a 4-wheeler, all else being equal. Aerodynamic drag can be minimised by designing a fully enclosed body that reduces the
drag coefficient In fluid dynamics, the drag coefficient (commonly denoted as: c_\mathrm, c_x or c_) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water. It is used in the drag e ...
, but given that this can be a highly technical thing to achieve especially for the amateur builder, and given that some aerodynamic drag is inevitable, a heavier cart will always do better than a lighter one with the same drag coefficient - its
terminal velocity Terminal velocity is the maximum velocity (speed) attainable by an object as it falls through a fluid (air is the most common example). It occurs when the sum of the drag force (''Fd'') and the buoyancy is equal to the downward force of gravit ...
will be higher. For this reason there are usually class weight limits in most controlled forms of the sport. Since some of the
potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potentia ...
due to gravity must be converted to the
kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its accele ...
of the rotating wheels, a vehicle with lighter wheels will accelerate faster than one with heavier wheels. If a race is started on some form of ramp, having a tail-heavy car can also improve final acceleration, as the effective height of the centre of gravity of the vehicle is raised.


See also

* Buggy at Carnegie Mellon University * Catterline Cartie Challenge * Cyclekart *
Goodwood Festival of Speed The Goodwood Festival of Speed is an annual motorsports festival featuring modern and historic motor racing vehicles taking part in a hillclimbing, hill climb and other events, held in the grounds of Goodwood House, West Sussex, England, in l ...
(hosted its own soapbox derby between 2000 and 2004) * Lotus 119 * Pinewood Derby *
Pushcart derby The Pushcart derby is a popular sporting event held every August in Jamaica where homemade carts that are used for street vending, to transport items or as a racing cart take part in races like the American soap box races. The carts have been clo ...
in
Jamaica Jamaica (; ) is an island country situated in the Caribbean Sea. Spanning in area, it is the third-largest island of the Greater Antilles and the Caribbean (after Cuba and Hispaniola). Jamaica lies about south of Cuba, and west of His ...
that uses street vending carts. *
Soap Box Derby The Soap Box Derby is a youth soapbox car racing program which has been run in the United States since 1933. World Championship finals are held each July at Derby Downs in Akron, Ohio. Cars competing in this and related events are unpowered, ...
*
Street luge Street luge is an extreme gravity-powered activity that involves riding a street luge board (sometimes referred to as a sled) down a paved road or course. Street luge is also known as land luge or road luge. Like skateboarding, street luge is o ...


References


External links

*
"The Object at Hand," Smithsonian Magazine, May 1995
{{DEFAULTSORT:Gravity Racer Physical activity and dexterity toys Racing vehicles