I got this answer from wiki "A free-falling object achieves its terminal velocity when the downward force of gravity (Fg) equals the upward force of drag (Fd). This causes the net force on the object to be zero, resulting in an acceleration of zero"
What i dont understand is if the upward force and downward are equal while falling, then the object should not be moving and should remain stationary!!!
What i dont understand is if the upward force and downward are equal while falling, then the object should not be moving and should remain stationary!!!
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When a object falls from rest it's speed increases as soon as it is released. At the end of the first second its velocity will be 9.81 ms-1 and at the end of the second second it will have increased to 19.6 ms-1. Clearly then, there is a change in velocity and this means that the object has accelerated. If it has accelerated then it must be experiencing a force and this force is mg or your Fg acting downwards.
However, because the object has some shape it will experience a drag force, Fd that acts in the opposite direction to Fg. The thing to remember about this drag force is that the greater the velocity of the falling object then the bigger this drag force will be. So, while the force due to gravity, Fg, remains constant, the drag force does not: as the objects speed increases the drag force also increases.
Eventually, the falling object is moving so fast that the drag force, Fd now equals Fg. So, at this point Fg acts downward and Fd acts upward and they now become equal and opposite. This means that they exactly cancel one another out and the NET force on the object becomes zero.
If the NET force is zero, then this must mean that a, the acceleration, must also be zero (from: F =ma) because the mass of the object can't be zero. So, with zero acceleration It will fall at a constant velocity called the terminal velocity at whatever velocity it had just before it reached the Fg = Fd condition.
So, it will not stop in mid air, but will continue to move at the speed it had just before the two forces become equal and opposite.
However, because the object has some shape it will experience a drag force, Fd that acts in the opposite direction to Fg. The thing to remember about this drag force is that the greater the velocity of the falling object then the bigger this drag force will be. So, while the force due to gravity, Fg, remains constant, the drag force does not: as the objects speed increases the drag force also increases.
Eventually, the falling object is moving so fast that the drag force, Fd now equals Fg. So, at this point Fg acts downward and Fd acts upward and they now become equal and opposite. This means that they exactly cancel one another out and the NET force on the object becomes zero.
If the NET force is zero, then this must mean that a, the acceleration, must also be zero (from: F =ma) because the mass of the object can't be zero. So, with zero acceleration It will fall at a constant velocity called the terminal velocity at whatever velocity it had just before it reached the Fg = Fd condition.
So, it will not stop in mid air, but will continue to move at the speed it had just before the two forces become equal and opposite.
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The forces are equal means that the body cannot ACCELERATE, it is perfectly able to keep moving at a constant velocity, which is what happens at terminal velocity