Naturally Falling
Misconception:
A common misconception is that gravity is not a force and that falling is a natural motion that does not require a force. Among students, the thought that things fall is because nothing is holding them up, there is a lack of strength and effort, and things fall because of their weight (without recognizing that weight is the force of gravity acting upon them). For students who hold on to the idea that things just naturally fall, no force is necessary. Even some adults hold on to these misconceptions. Others go as far as saying that gravity only affects an object when it starts to fall and ceases when the object lands on the ground or other mode of support. (Driver et al. 1994) Some students and even adults, hold on to the misconception that heavier objects fall faster than lighter objects because they presume them to have a bigger acceleration due to gravity.

Many of these misconceptions about falling objects stem from what’s called the "commonsense theory of motion" (Hayes 1979; Ogborn 1985). Through experience and previous observation, individuals formulate models in their mind of what’s happening around them. A tenet of that theory is that:
“Everything needs support except the ground that gives support but is not itself supported. Air and water can also support things but this is often only partial. To support something needs "strength" or "effort" or both. If the strength of a support is not enough it may break or yield. Thus a shelf supports heavy objects by being ’strong’ whereas a bird supports itself by its own effort of flying. People support things when carrying them through their own strength and effort. . . . The [commonsense] law of falling is that, having started to fall, things fall more rapidly the higher up they start and the heavier they are.” (Bliss et al., 262)


What is Gravity?


Because of gravity, if you drop something, it falls down. What is gravity exactly? Well even though we don’t know what gravity is, we do know how it behaves. Gravity is an attractive force between all objects in the universe. It basically pulls together all matter. Mass is measured by how much matter is in an object. The more massive an object, the more gravitation pull it exerts.

Sir Isaac Newton first observed that a force was needed for an object to change the speed or direction of a moving object. He also observed that this gravitational force is what must make an apple fall from a tree, or humans living on a rotating planet without getting flung off. Newton deducted that gravity forces existed between all objects.

Newton’s law of gravity expresses how two objects interact with one of other. This is represented by the gravitational equation which says that force of gravity (Fg) between to objects is proportional to the product of the two masses (m1 and m2), and inversely proportional to the square of the distance (r) between their centers of mass (NASA). All of which would be multiplied by the gravitation constant (G) which 6.673x10-11 m3/(kg s2) (Palen, 2012).
Mathematically the gravitational equation can be stated,
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The effects of gravity extend from each object into space in all directions, and for an infinite distance. Apart from mass, gravity is affected by distance. The strength of gravity reduces quickly with distance. That is why we are stuck to earth and not pulled into the Sun. we are closer to earth so we never really feel the affect of the Sun’s gravitational pull. However, we know there is gravitational pull from the Sun because the suns gravity keeps Earth in its orbit (NASA).


A few other misconceptions about gravity and falling objects:
1- Things fall from a lack of support
2- Strength and effort prevent falling
3- Gravity is not a force
4- Heavier objects fall faster
5- Gravity attracts only heavy, slow, or inactive objects
6- Gravity acts upward
7- Gravity is related to movement, proximity to Earth, or magnetism
8- The moon has no gravity
9- Gravity is determined by the thickness of the atmosphere
10- Gravity is stronger between the most distance objects
11- Space shuttle astronauts are weightless because there is no gravity above the Earth
12- There is no gravity in space

Some videos about some of these misconceptions:
http://www.youtube.com/watch?v=_mCC-68LyZM

http://www.youtube.com/watch?v=TdEWmy-SmwE

References:
Bar, V., Zinn, B., Goldmuntz, R., & Sneider, C. 1994, "Children’s Concepts about Weight and Free Fall," Science Education, 78(2), 149.

Bliss, J., Ogborn, J., & Whitelock, D. 1989, "Secondary School Pupils’ Commonsense Theories of Motion," International Journal of Science Education, 11(3), 262.

Driver, R., Squires, A., Rushworth, P., Wood-Robinson, V. 2002, “Making Sense of Secondary Science: Research into Children’s Ideas, 163-167

Hayes, P. 1979, "The Naïve Physics Manifesto," in Expert Systems in the Microelectronic Age, D. Mitchie (Editor), Edinburgh, UK: Edinburgh University Press, 242.

Ogborn, J. 1985, "Understanding Students’ Understanding: An Example from Dynamics," European Journal of Science Education, 7(2), 141.a

Palen, S., Kay, L., Smith, B., Blumenthal, G. 2012, “Understanding Our Universe”, 52,59-66

http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/1-what-is-gravity.html

http://spaceplace.nasa.gov/what-is-gravity/

http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question30.html