![]() ![]() ![]() Torrential downpours in tropical regions can produce very large raindrops of even 2 ml or Ø 8 mm equivalent diameter. Newton's First Law beautifully says this.While rain drop size varies based on rain intensity and rainfall speed, one standardized laboratory drop of H2O is defined as 0.05 ml or about Ø 2.3 mm (1 ml = 20 drops), Rain drop sizes found in nature vary widely as shown below:ĭrizzle raindrop sizes can be very small, 0.00004 ml or Ø 0.2 to 0.5 mm, where they are not able to produce any measurable readings in most rain gauges. This is what happens in the case of raindrop, it continues to fall because the two forces acting on it cancels out and some other force must stop it, since there isn't any other force it continues to fall. ![]() We can certainly say that if it were to stop, it is due to some kind of force, we aren't giving any force, so it must move. So there is no new force (ie) only two forces are acting Drag and Gravity.Ĭonsider a space where there is no atmosphere and no gravity due to any planet, if we throw a ball does it stop or does it move continuously? Ĭonsider the moment when the net force becomes zero, at that moment, it is falling, if it was to stay put at that moment, then a huge force must act in the direction opposite to which it is falling ,but there is no such force, drag doesn't achieves this, because it has an important job of tackling the gravity. So at one point, the net force acting is zero, it won't accelerate, it's falling, it's velocity doesn't change. ![]() $\rho$ is the density of the medium through which rain drop is moving.Īs the body starts from rest ,it's velocity increases due to $F_g=mg$ (Gravitational Force)Īs the velocity increases, Drag force increases as a square term. Mathematically, the movement of a drop can be described as Thus, this is a particular case of the Newton's second law (not to be confused with the Newton's first law, which defines the intertial reference frames.) If the forces on an object add to zero (in an inertial reference frame) it experiences zero acceleration and hence moves with a constant velocity (but not necessarily zero velocity). So how come the rain drop keeps falling when net force acting on it becomes zero? How the air resistance and other forces stops the rain drop from acquiring accelerated downward motion? My confusion regarding the matter is that if the net force acting on a body (here the rain drop) is zero then it should remain suspended in air rather than falling towards the earth. The falling drop increases speed until the resistance of the air equals the pull of gravity, at which point the drop begins to fall at a constant speed, its terminal velocity. I was not satisfied by the explanation So I searched the internet which too had similar explanations: Thus the net force on the drop is zero so it falls down with a constant velocity. Rain drop falls with a constant velocity because the weight(which is the force of gravity acting on body) of the drop is balanced by the sum of the buoyant force and force due to friction(or viscosity )of air. ![]()
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