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7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonisha 1/15
Physics of SurfingEnergetics of a Surfer
David T. Sandwell(http://topex.ucsd.edu)
Four styles of surfing
Waves Big swell coming? (storms) What makes sets? (dispersion)
Why is Blacks Beach good for surfing?(refraction)
Riding waves catching the wave (speed)
dropping-in (energy conservation)
tube riding (tapping wave energy) need more speed (surfboard drag)
1 2 kg 1 kg
Which ball is going faster when it reaches the bottom?
(a) (b)
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonisha 2/15
Which ball is going faster when it reaches the bottom?
(a) (b) (c)
conservation of energy(assume no friction)
kinetic energy + potential energy = constant
mgH=1
2mv
2m
m
v
H
mv
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonisha 3/15
optimal skateboard ramp(The brachistochrone problem)
What is the best ramp shape for the minimum time down?
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonisha 4/15
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonisha 5/15
60 ft
35 mph
24 ft22 mph15 ft
18 mph4.5 ft10 mph
ocean depth and breaker height - empirical
Hb- height of breaker
db- depth where wave
breaks
db
=1.28Hb
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonisha 6/15
Mavericks video
shallow water waves
cs = gd
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonisha 7/15
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonisha 8/15
breaking waves
db
surfers
empirical relation
Hb- height of breakerdb- depth where wave
breaks
db
=1.28Hb
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonisha 9/15
catching the wave
db
surfers
paddle speed
Hb- height of breakerdb- depth where wave
breaks
cb = 1.28gHb
paddle speed
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonish 10/15
dropping in
Hb
top of wave
bottom of wave
KEbottom= KEtop+ PE
1
2mvd
2=
1
2mcb
2+mgHb
vd2=cb
2+2gHb = 3.28gHb
g - acc. Gravity
cb- wave speedvd- surfer speed after drop
dropping in
59.827.217.023tow-in
35.216.010.08tube
27.912.77.95fun
15.26.94.31.5longboard
vd
(mph)
vd
(m/s)
cb
(m/s)
Hb
(m)
style
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonish 11/15
correction for surfer height
H' Hb
H'= Hb- 1/2 Hs
effective height = breaker height - 1/2 surfer height
- overhead waves are good- waist high waves are bad- short surfers and heavy boards have an advantage in small waves
Pipeline video
dropping in
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonish 12/15
dropping in
Hb
top of wave
bottom of wave
KEbottom= KEtop+ PE
1
2mvd
2=
1
2mcb
2+mgHb
vd2=cb
2+2gHb = 3.28gHb
g - acc. Gravity
cb- wave speedvd- surfer speed after drop
dropping in
59.827.217.023tow-in
35.216.010.08tube
27.912.77.95fun
15.26.94.31.5longboard
vd
(mph)
vd
(m/s)
cb
(m/s)
Hb
(m)
style
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonish 13/15
cutting across
back of wave
front of wave
vd !
cb
cb
2
vd
2=
1.28
3.28=cos
2!
!=~ 50
topview
This angle is independent ofwave height or wave speed!
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
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riding the wave
Suppose the surfer remains on the steepest part of the wave having
a slope s. What is the rate of potential energy increase supplied tothe surfer?
cb s
P E = sgcbside view
v(t)2=vd
2+ sgcb
o
t
! dt
v(t)2=3.28gHb +tsg 1.28gHb
How does speed increase
with time?
speed video
7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f
http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonish 15/15
the drag
v(t)2 = 3.28gHb + 1.13g
3 / 2 s Hb
1/ 2 t ! drag
total
velocity
= paddle
drop in+
-
slope of
the curlbreakerheight
duration
of ride
energy
dissipation
Future Research Are the best surf spots in areas of narrow continental margin?
Are sets real? What are the statistical properties of sets? Do setsbecome amplified when they reach shallow water?
How does the shape of the bottom translate into the perfect wave?
What is the terminal velocity for a given breaker height? (Can we establishthe magnitude of the drag term?)
Need to instrument surfers with intertial sensors.