![]() The most important physical factors affecting the shape of raindrops are the surface tension, gravitational force, drag and buoyant forces. The values of terminal velocities of different types of rain are summarized in Tables 3.3 and 3.4. In above equation, the parameters A and C D are not constant, are the functions of mass and velocity of the drop. It can be presented by the following expression:Ī = reference area used in the drag-force equation. In brief, the rain drops attain terminal velocity when gravitational, drag and buoyant forces acting on the drop become in balanced form. At terminal velocity stale the raindrop experiences no further acceleration and therefore rain drops fall at a constant velocity. By terminal velocity the raindrop hits the ground surface. The two forces, i.e., the drag force and gravitational force becomes in balance mode, when air resistance becomes equal to the weight of the raindrop.Īt this condition the drop attains an equilibrium speed, called terminal velocity. Simultaneously, the drag force of the surrounding air slows the drop’s speed. At high speeds the air resistance varies as the square of the velocity.įrom the cloud mass a falling raindrop picks up the speed because of gravity force. The smaller drops are spherical, while larger drops are flat from the bottom because of airflow. In general, most of the raindrops are fairly round. The air resistance depends on the shape of raindrop, the cross-sectional area of drop and the speed of raindrop. The air resistance that comes in contact with the water droplets as they fall, causes the drag force. ![]() The drag force retards the downward acceleration of raindrop. The gravity force increases the speed of falling raindrop. A stationary raindrop initially experiences the force due to acceleration due to gravity 9.8 m/s 2. When a raindrop falls to the ground surface, two forces, i.e., the gravity and drag forces act on it. Drizzle which drop size is less than 0.5mm falls at the speed of 2 m/s (0.5 mph). A large raindrop of about 5 mm size falls at the rate of 9 m/s (20 miles per hour). The heavier the drop, the greater will be the falling speed. The falling velocity of raindrop depends on its size and weight. The average size of raindrop is 6mm in diameter, i.e., the size of housefly. The water droplets falling from the cloud are the condensed water. And one of the components of the hydrologic cycle that begins from the water evaporation, formation of clouds in the atmosphere and ultimately falling on the ground surface. ![]() Rain is the liquid form of precipitation on the ground surface. This is most popular technique and is widely used. He also developed a calibration chart between the size of pellet and the size of raindrop, by which the average raindrop size can be obtained. The dried Hour globules are known as pellet. Several such wet globules of flour are formed during the rainfall, which are separated from each other and are dried.
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