Free-Fall Motion
Question:

A free falling object is an object that is falling under the sole influence of gravity. Any object that is being acted upon only by the force of gravity is said to be in a state of free fall. There are two important motion characteristics that are true of free-falling objects:

  • Free-falling objects do not encounter air resistance.
  • All free-falling objects (on Earth) accelerate downwards at a rate of 9.8 m/s/s (often approximated as 10 m/s/s for back-of-the-envelope calculations)

Because free-falling objects are accelerating downwards at a rate of 9.8 m/s/s, a dot diagram of its motion would depict an acceleration. The dot diagram at the animation shows the acceleration of a free-falling object. The position of the object at regular time intervals - say, every 1 second - is shown. The fact that the distance that the object travels every interval of time is increasing is a sure sign that the ball is speeding up as it falls downward. If an object travels downward and speeds up, then its acceleration is downward.


As mentioned in BLOSSOMS lesson:


http://blossoms.mit.edu/videos/lessons/free_fall#lesson-detail-tab-download

 

The kinematic equations that describe any object's motion are:

 

y is the distance

V0 is the initial velocity

V is the final velocity

a is the gravity acceleration

 

  1. A package is dropped from an air balloon two times. In the first trial the distance between the balloon and the surface is H and in the second trial 4H. Compare the time it takes for the package to reach the surface in the second trial to that in the first trial?

 

2 People tried to answer this question

The time in the second trial is four times less.

The time in the second trial is two times greater.

The time the same in both trials because it doesn’t depend.

The time in the second trial is four times greater.

correct answer, good student 

It's not a constant speed, you should use the kinematics equation with acceleration.

The time depends in the distance:

It's not a constant speed, you should use the kinematics equation with acceleration.



Comments:
1.  Auinat Mahmud (23.05.2017 pm 10.27.47)
Free fall question

good question

2.  aunallah nazek (26.06.2017 am 04.37.12)
cooment

Hello;

first of all the scientific background is very claer,arranged and understandable.

The video you attached is not clear,the writing is too small,and the video is very fast.my field is not physics and when i watched the animation i felt that it doesnt contribute to understanding the subject. i suugest to add a slow video that can help students to understand the meaning of accleration by showig each step slolwy,and animation to be more coherent to the question.

your question is phrased clearly and the answers are clear and short,but i think that there is place for questions of higher level of thinking,

 At last, the overall question is good but the subject could be prsented in more cerative way

Thank you



History of edits
Edited BY: Mahmud Auinat Edit Date: 2017-06-12 17:58:16
Edited BY: Mahmud Auinat Edit Date: 2017-05-31 12:22:15
Edited BY: Mahmud Auinat Edit Date: 2017-05-24 13:44:55
Edited BY: Mahmud Auinat Edit Date: 2017-05-23 22:35:14
Edited BY: Mahmud Auinat Edit Date: 2017-05-23 22:22:57
Edited BY: Mahmud Auinat Edit Date: 2017-05-23 22:20:36
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