Problem 3. We learnt in class that surface tension forces enable water striders to walk on water (Fig. 3). Assuming that the body weight of the water strider is supported by its 4 hind legs, and that the average hind leg is 22 mm long, with a superhydrophobic surface that contacts the water at the middle of the leg at a contact angle 0 = 160°: 1. What is the maximum weight a water strider can have without sinking? 2. Unfortunately, our waterways has been continually polluted with urban waste, which contains surfactant molecules such as laundry detergent. This reality means that organ- isms around us need to adapt to survive. How much weight does the water strider need to lose in order to survive in a water body with surfactant concentration C, = 0.1 mM? 75 (a) (b) 70 - 45 · 40 - 0.1 0.001 0.01 10 CJMM Figure 3: (a) Distortion of the water surface generates the surface tension force needed to sup- port the water strider's body weight. (b) Surface tension of water as a function of surfactant concentration. Surface tension/mN m-1
Problem 3. We learnt in class that surface tension forces enable water striders to walk on water (Fig. 3). Assuming that the body weight of the water strider is supported by its 4 hind legs, and that the average hind leg is 22 mm long, with a superhydrophobic surface that contacts the water at the middle of the leg at a contact angle 0 = 160°: 1. What is the maximum weight a water strider can have without sinking? 2. Unfortunately, our waterways has been continually polluted with urban waste, which contains surfactant molecules such as laundry detergent. This reality means that organ- isms around us need to adapt to survive. How much weight does the water strider need to lose in order to survive in a water body with surfactant concentration C, = 0.1 mM? 75 (a) (b) 70 - 45 · 40 - 0.1 0.001 0.01 10 CJMM Figure 3: (a) Distortion of the water surface generates the surface tension force needed to sup- port the water strider's body weight. (b) Surface tension of water as a function of surfactant concentration. Surface tension/mN m-1
Chapter2: Loads On Structures
Section: Chapter Questions
Problem 1P
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Transcribed Image Text:Problem 3. We learnt in class that surface tension forces enable water striders to walk on
water (Fig. 3). Assuming that the body weight of the water strider is supported by its 4
hind legs, and that the average hind leg is 22 mm long, with a superhydrophobic surface
that contacts the water at the middle of the leg at a contact angle 0 = 160°:
1. What is the maximum weight a water strider can have without sinking?
2. Unfortunately, our waterways has been continually polluted with urban waste, which
contains surfactant molecules such as laundry detergent. This reality means that organ-
isms around us need to adapt to survive. How much weight does the water strider need
to lose in order to survive in a water body with surfactant concentration C,
= 0.1 mM?
75
(a)
(b)
70 -
45 ·
40 -
0.1
0.001
0.01
10
CJMM
Figure 3: (a) Distortion of the water surface generates the surface tension force needed to sup-
port the water strider's body weight. (b) Surface tension of water as a function of surfactant
concentration.
Surface tension/mN m-1
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