Unravelling the secrets of swing in cricket with physics (GS Paper 3, Science and Technology)
Context:
- Cricket matches under day-night conditions are associated with shifts in humidity and moisture.
- Most captains winning the toss in day-night matches prefer to bowl first and bat second.
Dew factor:
- The water vapour condenses on the ground in the evening, creating a slippery surface. As a result, spinners have a harder time getting the ball to grip and fast bowlers have more trouble producing swing and seam. Fielding on a slippery ground is also obviously harder.
- As a result of these changes in ground conditions, batters appear to have an advantage under dew, as they face less swing, less spin, and less lateral movement of the ball.
- Sometimes, fast bowlers release the ball at a certain angle into its flight path. As a result, air flow is turbulent on one side of the ball and streamlined on the other. This causes a sudden pressure difference that causes the ball to deviate from its path in a motion called its swing.)
- Batters also expect the ball to skid off the bat under dew, and expect opportunities to maintain a higher run rate with less effort.
Friction & dew:
- A closer analysis of the physics of friction suggests that the belief that dew always increases slipperiness is scientifically flawed.
- Friction is reduced only when the water film in between is thick enough to reduce the amount of physical contact between two surfaces.
- When the thickness is below a certain threshold, it increases the overall friction because the water molecules interact more strongly with the two surfaces due to adhesive forces.
- A recent study led by Liang Peng of the University of Amsterdam found that the coefficient of friction doubled when humidity was increased by 20% and decreased only thereafter. The scientists attributed this to hydrogen bonds that formed as a result of electrostatic forces.
- Thus, in moist weather, the coefficient of friction increases, advantaging the bowler. This may have been why India’s batters lost three early wickets in the match against Australia in Chennai.
Impact on bowling speed:
- The work of German physicist Richard Stribeck on friction has shown that for a given layer of lubricant, friction increases when the speed of interaction between two surfaces is higher than a threshold value.
- So in wet conditions, fast bowlers can use this feature to force the ball to grip more by launching it at a higher speed.
Effects of weather conditions:
- Cricketers have also displayed the belief that the dew content negatively influences swing.
- In specific weather conditions, there is one optimum bowling speed, one optimum seam angle, and one desirable spin rate. If the delivery speed is less than the optimal value, the spin will need to be increased to generate a certain amount of swing.
- The ball’s trajectory through the air also creates an asymmetric flow field around its surface, which produces the so-called Magnus force. The strength of the force increases when the temperature is lower and there is more moisture in the air. That is, changes in air density have a strong influence on the swing.
- For example, if the temperature drops from 25º C to 15° C, the air density will increase by 4%, and the ball’s deviation due to swing can increase by an inch. The effect is minor but the outcomes can be significant.
- When the air temperature drops, sunlight causes less turbulence in the air above the pitch, giving bowlers more control. The success of Indian bowlers Mohammed Shami and Jasprit Bumrah in the ongoing ICC Men’s Cricket World Cup may well be due to this effect.
- A misunderstanding of the impact of dew can leave batters overconfident, and cause them to get out caught when trying to hit what they believe to be ‘easy’ balls for boundaries.
- Instead, their chances can improve if they maintain a particular level of moisture content on their gloves and soles, while avoiding six-hitting.
DLS method:
- Cricketers playing a game in wet weather also need to contend with the peculiarities of the Duckworth-Lewis-Stern (DLS) method.
- The prospect of rain forces captains to prefer risk-free play that preserves wickets. This is because the DLS method works with the ratio of runs scored to resources used, and the resources are the number of overs and wickets available.
- According to the DLS method, when setting a target, Team A’s score per unit resource is multiplied by Team B’s resources. The ‘worth’ of a ball and wicket in percentage terms are derived from data in a sliding four-year window.
- Key drawbacks of the DLS method are that it can’t factor in the quantitative values of each team and that it favours teams that maintain a low run-rate and keep wickets in hand.
- In addition, the method also neglects the fact that, when after rain, Team B will have to play with a very damp pitch, which will influence its run-making abilities even while advantaging Team A, which can reap more gains if it knows how to use friction to achieve its goals.
Way Forward:
- For these reasons, cricketers must be made fully aware of the intricacies of playing with dew and moisture, and ensure future wins.
Deforestation in Maritime Continent may make El Nino events more complex and harder to predict
(GS Paper 1, Geography)
Why in news?
- Deforestation in the Maritime Continent (MC) can strengthen subtropical El Nino-Southern Oscillation (ENSO) dynamics, causing more Central Pacific and multi-year ENSOs, according to a new climate modelling study.
- The archipelagos of Indonesia, Borneo, New Guinea, the Philippine Islands, the Malay Peninsula and the surrounding seas are part of the MC region.
How deforestation alters ENSO?
- Deforestation in the region has the potential to alter ENSO’s complexity, making El Nino more complex and less predictable.
- ENSO is an important climate phenomenon on Earth due to its ability to change the global atmospheric circulation, which in turn influences temperature and precipitation across the globe.
- Logging trees is a common land-use change, especially in tropical regions like the MC. However, deforestation reduces evapotranspiration and alters surface albedo, which measures how much sunlight the Earth's surface reflects.
- As surface albedo warms the ambient environment, this further impacts land-atmosphere-ocean interactions to modify the local climate.
- These local effects have the ability to affect land-atmosphere interactions, such as the land-sea breeze.
Basis of research:
- Researchers used the community Earth system model to simulate hypothetical future deforestation over 100 years, converting native broadleaf evergreen and deciduous trees to warm-season grasses.
- When compared to control experiments, the deforestation model increased the occurrence of the Central Pacific and multi-year types of ENSO.
- This change in the complexity of the climate phenomenon can be attributed to the MC’s intensification of subtropical ENSO dynamics.
More complex El Nino:
- The likelihood of Central Pacific type El Nino events occurring increased by 11.7 per cent as a result of deforestation compared to background levels in the models, while La Nina events were exacerbated by 14.6 per cent in the same simulations.
- Further, if deforestation continues, more multi-year La Nina events are likely to occur in the coming decades. Simulations suggest a 13.8 per cent increase in La Nina events. Multi-year El Nino events may increases from 40.2-44.7 per cent after deforestation.
- A study has found that five out of six La Nina events since 1998 have lasted two to three years. Ten multi-year La Nina events over the past century had an accelerated trend, with eight of these occurring after 1970.
- The two types of multiyear La Nina events over this time period followed either a super El Nino or a central Pacific El Nino.
Global carbon stack:
- The United Nations’ Food and Agriculture Organization (FAO) estimated that around 420 million hectares (ha) of forest were lost between 1990 and 2020. Even though the rate of deforestation has declined, it was still 10 million ha per year in 2015–2020.
- Forests contain 662 billion tonnes of carbon, which is more than half the global carbon stock in soils and vegetation.
- Despite a continued reduction in area, forests absorbed more carbon than they emitted in 2011–2020 due to reforestation, improved forest management and other factors, stated State of the World’s Forests 2022 by FAO.
