Editing Surfing (section)

== The physics of surfing{{anchor|Physics_of_surfing}} ==
{{Multiple image
|align=right |direction=vertical |width=
|image1=Nazaré, Portugal (Unsplash 7bt4ngmSu9Y).jpg |caption1=[[Tow-in surfing]] in [[Nazaré, Portugal]]
|image2=Praia do Norte, Nazaré, Portugal (33830450815).jpg |caption2=Giant [[breaking wave]]s in [[Praia do Norte (Nazaré)|Praia do Norte]]
|image3=Can you see the surfer? (33988985575).jpg |caption3=The [[Praia do Norte (Nazaré)|Praia do Norte, Nazaré]] (''North Beach'') was listed in the [[Guinness World Records]] for the biggest waves ever surfed.
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The physics of surfing involves the physical oceanographic properties of wave creation in the surf zone, the characteristics of the surfboard, and the surfer's interaction with the water and the board.

=== Wave formation ===
[[Ocean wave]]s are defined as a collection of dislocated water parcels that undergo a cycle of being forced past their normal position and being restored back to their normal position.<ref name=Talley2011 /> Wind causes ripples and [[Eddy (fluid dynamics)|eddies]] to form waves that gradually gain speed and distance (fetch). Waves increase in energy and speed and then become longer and stronger.<ref name=Scarfe2009 /> The fully-developed sea has the strongest wave action that experiences storms lasting 10-hours and creates {{Convert|15|m|ft|abbr=on|sigfig=3}} wave heights in the open ocean.<ref name=Talley2011 />

The waves created in the open ocean are classified as deep-water waves. Deep-water waves have no bottom interaction and the orbits of these water molecules are circular; their wavelength is short relative to water depth and the velocity decays before reaching the bottom of the water basin.<ref name=Talley2011 /> Deep water waves are waves in water depths greater than half their wavelengths.<ref>{{cite web |title=Wave Energy and Wave Changes with Depth |url=https://manoa.hawaii.edu/exploringourfluidearth/physical/waves/wave-energy-and-wave-changes-depth#:~:text=Deep%2Dwater%20waves%20are%20waves,%3E%201%2F2%20L). |access-date=21 September 2024}}</ref> Wind forces waves to break in the deep sea.{{clarify|date=February 2021}}

Deep-water waves travel to shore and become shallow-water waves when the water depth is less than half of their wavelength, and the wave motion becomes constrained by the bottom, causing the orbit paths to be flattened to [[ellipse]]s. The bottom exerts a frictional [[Drag (physics)|drag]] on the bottom of the wave, which decreases the celerity (or the speed of the waveform), and causes refraction. Slowing the wave forces it to shorten which increases the height and steepness, and the top (crest) falls because the velocity of the top of the wave becomes greater than the velocity of the bottom of the wave where the drag occurs.<ref name=Talley2011>{{cite book|last=Talley |first=Lynne D. |title=Descriptive Physical Oceanography: An Introduction |date=2011 |publisher=Academic Press |isbn=978-0-08-093911-7 |pages=223–244 |chapter=Chapter 8. Gravity Waves, Tides, and Coastal Oceanography }}</ref>

The surf zone is the place of convergence of multiple waves types creating complex wave patterns. A wave suitable for surfing results from maximum speeds of {{Convert|5|m/s|ft/s}}. This speed is relative because local onshore winds can cause waves to break.<ref name=Scarfe2009 /> In the surf zone, shallow water waves are carried by global winds to the beach and interact with local winds to make surfing waves.<ref name=Scarfe2009 /><ref name=Madsen1997 />

Different onshore and off-shore wind patterns in the surf zone create different types of waves. Onshore winds cause random wave breaking patterns and are more suitable for experienced surfers.<ref name=Scarfe2009 /><ref name=Madsen1997>{{cite journal |last1=Madsen |first1=P.A. |author2=O.R. Sørensen, and H.A. Schäffer |date=1997 |title=Surf zone dynamics simulated by a Boussinesq type model. Part I. Model description of cross-shore motion of regular waves |journal=Coastal Engineering |volume=32 |issue=4 |pages=255–287 |doi=10.1016/S0378-3839(97)00028-8|bibcode=1997CoasE..32..255M |issn = 0378-3839}}</ref> Light offshore winds create smoother waves, while strong direct offshore winds cause plunging or large barrel waves.<ref name=Scarfe2009 /> Barrel waves are large because the water depth is small when the wave breaks. Thus, the breaker intensity (or force) increases, and the wave speed and height increase.<ref name=Scarfe2009 /> Off-shore winds produce non-surfable conditions by flattening a weak swell. Weak swell is made from surface gravity forces and has long wavelengths.<ref name=Scarfe2009 /><ref name=Edge2001>{{cite journal |last=Edge |first=Ronald |date=2001 |title=Surf Physics |journal=The Physics Teacher |volume=39 |issue=5 |pages=272–277 |doi=10.1119/1.1375464|bibcode=2001PhTea..39..272E }}</ref>

=== Wave conditions for surfing ===
Surfing waves can be analyzed using the following parameters: breaking wave height, wave peel angle (α), wave breaking intensity, and wave section length. The breaking wave height has two measurements, the relative heights estimated by surfers and the exact measurements done by physical oceanographers. Measurements done by surfers were 1.36 to 2.58 times higher than the measurements done by scientists. The scientifically concluded wave heights that are physically possible to surf are {{Convert|1 to 20|m|ft|abbr=on|sigfig=2}}.<ref name=Scarfe2009 />

The wave peel angle is one of the main constituents of a potential surfing wave. Wave peel angle measures the distance between the peel-line and the line tangent to the breaking crest line. This angle controls the speed of the wave crest. The speed of the wave is an addition of the propagation velocity vector (Vw) and peel velocity vector (Vp), which results in the overall velocity of the wave (Vs).<ref name=Scarfe2009 />

Wave breaking intensity measures the force of the wave as it breaks, spills, or plunges (a plunging wave is termed by surfers as a "barrel wave"). Wave section length is the distance between two breaking crests in a wave set. Wave section length can be hard to measure because local winds, non-linear wave interactions, island sheltering, and swell interactions can cause multifarious wave configurations in the surf zone.<ref name=Scarfe2009 />

The parameters breaking wave height, wave peel angle (α), and wave breaking intensity, and wave section length are important because they are standardized by past oceanographers who researched surfing; these parameters have been used to create a guide that matches the type of wave formed and the skill level of surfer.<ref name=Scarfe2009>{{cite journal |last1=Scarfe |first1=Bradley E. |author2=Terry R. Healy, and Hamish G. Rennie |date=2009 |title=Research-Based Surfing Literature for Coastal Management and the Science of Surfing—A Review |url=http://www.jcronline.org/doi/full/10.2112/07-0932.1 |journal=Journal of Coastal Research |volume=25 |issue=3 |pages=539–557 |doi=10.2112/07-0958.1|s2cid=145159559 |doi-access=free }}</ref>

{| class="wikitable"
|+ Table 1: Wave type and surfer skill level<ref name=Scarfe2009 />
! Skill level !! Peel angle (degrees) !! Wave height (meters) !! Section speed (meters/second) !! Section length (meters) !! General locations of waves
|-
| Beginner|| 60-70 || 2.5 || 10|| 25 || Low Gradient Breaks;{{citation needed|date=May 2019}} [[Atlantic Beach, Florida]]
|-
| Intermediate || 55 || 2.5|| 20 || 40 || [[Bells Beach, Victoria|Bells Beach]]; [[Australia]]{{citation needed|date=May 2019}}
|-
| Competent|| 40-50 || 3 || 20 || 40-60 || [[Kirra, Queensland|Kirra Point]]; [[Burleigh Heads, Queensland|Burleigh Heads]]
|-
| Top Amateur || 30 || 3 || 20 || 60 || [[Pecatu#Bingin Beach|Bingin Beach]]; [[Pecatu#Padang Padang Beach|Padang Padang Beach]]
|-
| Top World Surfer || >27 || 3 || 20 || 60 || [[Banzai Pipeline]]; [[Shark Island (Cronulla Beach)|Shark Island]]
|}

Table 1 shows a relationship of smaller peel angles correlating with a higher skill level of the surfer. Smaller wave peel angles increase the velocities of waves. A surfer must know how to react and paddle quickly to match the speed of the wave to catch it. Therefore, more experience is required to catch low peel angle waves. More experienced surfers can handle longer section lengths, increased velocities, and higher wave heights.<ref name=Scarfe2009 /> Different locations offer different types of surfing conditions for each skill level.

=== Surf breaks ===
A [[surf break]] is an area with an obstruction or an object that causes a wave to break. Surf breaks entail multiple scale phenomena. Wave section creation has microscale factors of peel angle and wave breaking intensity. The micro-scale components influence wave height and variations on wave crests. The mesoscale components of surf breaks are the ramp, platform, wedge, or ledge that may be present at a surf break. Macro-scale processes are the global winds that initially produce offshore waves. Types of surf breaks are headlands (point break), beach break, river/estuary entrance bar, reef breaks, and ledge breaks.<ref name=Scarfe2009 />

==== Headland (point break) ====
A [[headland]] or point break interacts with the water by causing refraction around the point or headland. The point absorbs the high-frequency waves and long-period waves persist, which are easier to surf. Examples of locations that have headland or point break-induced surf breaks are Dunedin (New Zealand), Raglan (New Zealand), Malibu (California), Rincon (California), and Kirra (Australia).<ref name=Scarfe2009 />

==== Beach break ====
A beach break is an area of open coastline where the waves break over a sand-bottom. They are the most common, yet also the most volatile of surf breaks. Wave breaks happen successively at beach breaks, as in there are multiple peaks to surf at a single beach break location. Example locations are Tairua and Aramoana Beach (New Zealand) and the Gold Coast (Australia).<ref name=Scarfe2009 />
<gallery>
JunoBeachBeachBreak.jpg|A group of surfers surfing a beach break in [[Juno Beach, Florida]].
</gallery>

==== River or estuary entrance bar ====
A river or estuary entrance bar creates waves from the ebb-tidal delta, sediment outflow, and tidal currents. An ideal estuary entrance bar exists in Whangamata Bar, New Zealand.<ref name=Scarfe2009 />

==== Reef break ====
A reef break is conducive to surfing because large waves consistently break over the reef. The reef is usually made of coral, and because of this, many injuries occur while surfing reef breaks. However, the waves that are produced by reef breaks are some of the best in the world. Famous reef breaks are present in Padang Padang (Indonesia), Pipeline (Hawaii), Uluwatu (Bali), and Teahupo'o (Tahiti).<ref name=Scarfe2009 /><ref>{{cite web|last1=Hurt|first1=Garek|title=The differences between beach breaks, point breaks, and reef breaks |url=https://www.degree33surfboards.com/blogs/gettin-pitted/14071029-the-differences-between-beach-breaks-point-breaks-and-reef-breaks|website=Degree 33 Surfboards|access-date=26 November 2017}}</ref>

==== Ledge break ====
A ledge break is formed by steep rocks ledges that make intense waves because the waves travel through deeper water then abruptly reach shallower water at the ledge. Shark Island, Australia is a location with a ledge break. Ledge breaks create difficult surfing conditions, sometimes only allowing body surfing as the only feasible way to confront the waves.<ref name=Scarfe2009 />

=== Jetties and their impacts on wave formation in the surf zone ===
{{expert needed|1=Limnology and Oceanography|reason=Contents of this section are incomprehensible. Source is paywalled |date=February 2021}} 
[[Jetty|Jetties]] are added to bodies of water to regulate erosion, preserve navigation channels, and make harbors. Jetties are classified into four different types and have two main controlling variables: the type of delta{{clarify|What is the delta in this context?|date=February 2021}} and the size of the jetty.<ref name=Scarfe2003>{{cite journal |last1= Scarfe |first1=B.E. |author2=M.H.S. Elwany, K.P. Black, and S.T. Mead |title=Categorizing the Types of Surfing Breaks around Jetty Structures |url=http://escholarship.org/uc/item/09f405bq |journal=Scripps Institution of Oceanography Technical Report |date=7 March 2003 |pages=1–8}}</ref>

==== Type 1 jetty ====
The first classification is a type 1 jetty. This type of jetty is significantly longer than the surf zone width and the waves break at the shore end of the jetty. The effect of a Type 1 jetty is sediment accumulation in a wedge formation on the jetty. These waves are large and increase in size as they pass over the sediment wedge formation. An example of a Type 1 jetty is Mission Beach, San Diego, California. This 1000-meter jetty was installed in 1950 at the mouth of Mission Bay. The surf waves happen north of the jetty, are longer waves, and are powerful. The bathymetry of the sea bottom in Mission Bay has a wedge shape formation that causes the waves to refract as they become closer to the jetty.<ref name=Scarfe2003 /> The waves converge constructively after they refract and increase the sizes of the waves.

==== Type 2 jetty ====
A type 2 jetty occurs in an ebb-tidal delta, a delta transitioning between high and low tide. This area has shallow water, refraction, and distinctive seabed shapes that create large wave heights.<ref name=Scarfe2003 />

An example of a type 2 jetty is called "The Poles" in Atlantic Beach, Florida. Atlantic Beach is known to have flat waves, with exceptions during major storms. However, "The Poles" has larger than normal waves due to a 500-meter jetty that was installed on the south side of St. Johns. This jetty was built to make a deep channel in the river. It formed a delta at "The Poles". This is a special area because the jetty increases wave size for surfing when comparing pre-conditions and post-conditions of the southern St. Johns River mouth area.<ref name=Scarfe2003 />

The wave size at "The Poles" depends on the direction of the incoming water. When easterly waters (from 55°) interact with the jetty, they create waves larger than southern waters (from 100°). When southern waves (from 100°) move toward "The Poles", one of the waves breaks north of the southern jetty and the other breaks south of the jetty. This does not allow for merging to make larger waves. Easterly waves, from 55°, converge north of the jetty and unite to make bigger waves.<ref name=Scarfe2003 />

==== Type 3 jetty ====
A type 3 jetty is in an ebb-tidal area with an unchanging seabed that has naturally created waves. Examples of a Type 3 jetty occurs in “Southside” Tamarack, Carlsbad, California.<ref name=Scarfe2003 />

==== Type 4 jetty ====
A type 4 jetty is one that no longer functions nor traps sediment. The waves are created from reefs in the surf zone. A type 4 jetty can be found in Tamarack, Carlsbad, California.<ref name=Scarfe2003 />

=== Rip currents ===
{{main|Rip current}} 
[[Rip current]]s are fast, narrow currents that are caused by onshore transport within the surf zone and the successive return of the water seaward.<ref name=Dalrymple1978 /><ref name=Smith1995 />  The wedge bathymetry makes a convenient and consistent rip current of 5–10 meters that brings the surfers to the “take-off point” then out to the beach.<ref name=Scarfe2003 />

Oceanographers have two theories on rip current formation. The wave interaction model assumes that two edges of waves interact, create differing wave heights, and cause longshore transport of nearshore currents. The Boundary Interaction Model assumes that the topography of the sea bottom causes nearshore circulation and longshore transport; the result of both models is a rip current.<ref name=Dalrymple1978>{{cite journal |last=Dalrymple |first=Robert A. |date=1978 |title=Rip Currents and Their Causes |url=https://journals.tdl.org/icce/index.php/icce/article/viewArticle/3345 |journal=Coastal Engineering |volume=1 |issue=16 |pages=1414–1427|doi=10.1061/9780872621909.085 |isbn=9780872621909 }}</ref>

Rip currents can be extremely strong and narrow as they extend out of the surf zone into deeper water, reaching speeds from {{convert|0.5|m/s|ft/s||abbr=on|sigfig=2}} and up to {{convert|2.5|m/s|ft/s||abbr=on|sigfig=2}},<ref name=Smith1995 /><ref name=Bowen1969 /> which is faster than any human can swim. The water in the jet is sediment rich, bubble rich, and moves rapidly.<ref name=Smith1995 /> The rip head of the rip current has long shore movement. Rip currents are common on beaches with mild slopes that experience sizeable and frequent oceanic swell.<ref name="Bowen1969">{{cite journal |last=Bowen |first=Anthony J. |date=1969 |title=Rip Currents: Theoretical Investigations |journal=Journal of Geophysical Research |volume=74 |issue=23 |pages=5467–5477 |doi=10.1029/JC074i023p05467 |bibcode=1969JGR....74.5467B |url=http://chinacat.coastal.udel.edu/cieg682/protect/bowen-jgr69.pdf |url-status=dead |archive-url=https://web.archive.org/web/20100612115232/http://chinacat.coastal.udel.edu/cieg682/protect/bowen-jgr69.pdf |archive-date=12 June 2010 |df=dmy-all |citeseerx=10.1.1.463.6097 }}</ref>

=== On the surfboard ===
A longer [[surfboard]] of {{convert|300|cm|ft|abbr=on|sigfig=1}} causes more friction with the water; therefore, it will be slower than a smaller and lighter board with a length of {{convert|180|cm|ft|abbr=on|sigfig=1}}. Longer boards are good for beginners who need help balancing. Smaller boards are good for more experienced surfers who want to have more control and maneuverability.<ref name=Edge2001 />

When practicing the sport of surfing, the surfer paddles out past the wave break to wait for a wave. When a surfable wave arrives, the surfer must paddle extremely fast to match the velocity of the wave so the wave can accelerate him or her.<ref name=Edge2001 />

When the surfer is at wave speed, the surfer must quickly pop up, stay low, and stay toward the front of the wave to become stable and prevent falling as the wave steepens. The acceleration is less toward the front than toward the back. The physics behind the surfing of the wave involves the horizontal acceleration force (F·sinθ) and the vertical force (F·cosθ=mg). Therefore, the surfer should lean forward to gain speed, and lean on the back foot to brake. Also, to increase the length of the ride of the wave, the surfer should travel parallel to the wave crest.<ref name=Edge2001 />