Terminal Velocity
Question:

Terminal velocity is the term addressed to the maximal velocity of an object falling in any gas or liquid medium. The terminal velocity is a constant, specific for each object in a specific medium. Terminal velocity is a constant velocity, which means that the object is falling in a state of equilibrium. The forces that are applied to the object are:
Downward force – usually it is gravity

Buoyancy – acts as an upward force

Drag – this force is proportional to the velocity, and acts in the opposite direction. Drag is the very reason for terminal velocity. If an object is thrown down with an initial speed, higher than its terminal velocity in the medium, it will slow down until it reaches the terminal velocity.

Drag force is proportional with the medium's average density, the object's projected area, and the square the velocity:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

http://blossoms.mit.edu/videos/lessons/kite_flying_fun_art_and_scienc

While a drop of water is falling, only gravity and drag are taken under consideration.

Which of the following is the most correct?

2 People tried to answer this question

It is expected that the projected area of a raindrop will grow, thus making the drag force bigger as well.

The drop's attack angle is zero, thus the drag zeroes as well.

While falling in any atmosphere, density is more significant than the velocity.

While falling in an atmosphere, the significance to drag force, of the velocity overcomes the atmosphere density as velocity is increasing.

At small velocities, the square of the velocity can be less effecting the drag, than the linear proportion to the density. At later falling stage, the velocity keeps increasing while the density is remaining constant.

In a very viscous or very thin atmosphere the density is very significant, however in the middle range, the velocity becomes more significant as it is increased.  

A raindrop will slightly deform over time; However, the projected area will not change scientifically enough to overinfluence the velocity on the drag force. 

This answer is confusing terminology from BLOSSOMS lecture. Please watch again.



Comments:
1.  Khazim Alaa (25.06.2017 pm 06.58.29)
nice choice

A nice choice, an interesting subject that we encounter in many natural phenomena around us every day.

The explanations are clear, simple and short. You explain the phenomenon well, and the use of animation illustrates the explanation in a visual way and helps students to understand the phenomenon in a better way, especially how we see in the animation that the drags force increases gradually with speed increases.

Students can learn a lot from this experience, and to reach to a deep understanding of physical phenomena seen in their surroundings every day.

The feedback for the answers is excellent and relevant to the choice.

One example of the physical phenomenon from the students' world, is missing at the end of the paragraph.



History of edits
Edited BY: uri vainberg Edit Date: 2017-05-23 12:18:34
Edited BY: uri vainberg Edit Date: 2017-05-23 12:17:09
Created By: uri vainberg Edit Date: 2017-05-23 12:15:11
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