GRAVITY AND MOTION

 

To see my menu of all Muslim science posts, click https://muslimscience.blog/2016/08/10/mymenu/

“strobe light” diagram of a falling ball.

FALLING OBJECTS BOTCHED MEASUREMENTS
Ibn Bâjja (Avempace) fudged his measurements in his reaction force experiments of motion on an inclined plane, falsely claiming (for religious reasons that Allah created a perfect universe) that speed is proportional to the height from which an object was dropped. Actually, speed is proportional to the square root of the height from which an object was dropped.
When his experiment gave a different result, he threw out the experimental result and substituted what his religious beliefs told him the result must be.


The Jewish scholar Baruch ben Malka (1080 – 1164) repeated what Ibn Bâjjat had written. Baruch ben Malka converted from Judaism to Islam and changed his name to Hibat Allah Abu’l-Barakat al-Baghdadi.


EARTH HAS GRAVITY
A book written by either Alhazen (965–1039) or Abu ‘Abd Allah Muhammad ibn Ma’udh said things are attracted to the Earth [but so did Brahmagupta in the 7th century].

GRAVITY IS WEAKER AT A GREATER DISTANCE
Abū Sahl al-Qūhī (Kuhi), in the 10th century, agreed with Aristotle that the force of gravity got weaker as you got further away from the Earth.
The early 12th century Greek slave astronomer al-Khazini was an ethnic Greek captured in a Muslim invasion of the Byzantine Empire and sold into slavery and brought to what is now Turkmenistan, but his Muslim owner had given al-Khazini an education.
Al-Khazini likely borrowed from Aristotle the concept that gravity was less strong further away from the Earth (the center of the universe).
Al-Khazini’s works were known in the Muslim world but not in the Christian world.
After his death, Muslims rejected his teaching that gravity was weaker the further away you were from Earth.

EARTH’S GRAVITY HOLDS THE SUN IN ORBIT
Al-Biruni in the early 11th century agreed with Aristotle except that al-Biruni believed Earth’s gravity kept the sun and planets moving in perfectly circular paths around the Earth.

NON-MUSLIM CORRECTLY CLAIMED HEAVENLY BODIES OTHER THAN THE EARTH HAVE GRAVITY
Thābit ibn Qurra (826 – 901), living in Baghdad, was a Sabian (the name Muslims used to refer to members of an Abrahamic religion that venerated stars). He invented a theory of there being 2 types of attraction; one being attraction to the Earth, and the other being “between all parts of each element separately”, which is probably a theory that the sun and planets other than the Earth also have gravity.

NON-MUSLIMS CORRECTLY CLAIMED GRAVITY OF MOON AND SUN CAUSES TIDES
Pytheas, in 325 BC, was the first to write that tides are higher at full moon and at new moon.
The 2nd century BC Babylonian astronomer Seleucus of Seleucia linked tides to lunar attraction.


MUSLIMS FALSELY CLAIMED MOON AND SUN DO NOT HAVE GRAVITY
Al- Biruni (973 – 1048) did not know about the correlation between the moon and the tides until a Hindu told him. Since al-Biruni was certain that neither the sun nor the moon has gravity, he could not explain the reason why the moon correlated with the tides. Explaining higher tide at new moon would require knowing that both moon and sun have gravity, and knowing that gravity decreases with distance.

COMMENTARY ON ARCHIMEDES
In the 9th century, Al-Mahani wrote commentaries on Archimedes, but the Byzantines had been writing commentaries for many centuries, often by students seeking government careers. [A university degree was a requirement for many jobs in the Byzantine government.]

WEIGHING
Theophrastus (371 BC – 287 BC) wrote a book describing how to recognize minerals and gemstones.
Borrowing weighing techniques of Archimedes to detect counterfeiting, al-Biruni (973 – 1048) measured specific gravity of 18 metals, precious stones, and minerals.

Half of the specific gravity calculations were within plus or minus two percent of the current known values.

. He wrote a book describing how to recognize about 100 minerals and gemstones and the geographical areas where they were mined.

WEIGHING BY GREEK SLAVE OWNED BY A MUSLIM
In the early 12th century, the Greek slave al-Khazini, using the buoyancy (hydrostatics) principle of Archimedes, very accurately measured the specific gravities of 51 substances, especially gold, silver, gems and substances that might be used in counterfeiting them, but also the specific gravity of several liquids.
The Greek slave al-Khazini postulated that air has weight and that buoyancy (hydrostatics) rules of Archimedes also apply to air. In other words, light weight gases float on top of heavier weight gases if they don’t mix.
The Greek slave al-Khazini borrowed from Ptolemy the concept that air is less dense at higher altitudes.
The claim that the Greek slave al-Khazini computed how much the force of gravity was affected by the distance to the center of the Earth (by using a balance scale to measure the weight of a container of water at sea level and comparing that to its weight at a higher elevation) is a false claim because a balance scale cannot make this measurement (both sides of the balance scale are equally affected by the force of gravity) and spring scales were not invented yet.

MOMENTUM
In the 6th century, the Christian theologian John Philoponus (in the former Roman colony of Alexandria prior to its fall to Muslim Arabs) wrote that a body moves perpetually until a force is applied to stop it. This concept was copied 4 centuries later by Alhazen (965 – 1039). [Alhazen is famous mostly for his writings about optics.]
The Greek slave al-Khazini may have been the first to distinguish between mass and weight (which is mass multiplied by the force of gravity).
The Greek slave Al-Khazini borrowed from Aristotle a vague concept that did not distinguish between what we now call kinetic energy (which is proportional to mass multiplied by velocity squared) and what we now call momentum (which we now define as mass multiplied by velocity).

MOTION IN A VACUUM
The Christian theologian John Philoponus (in 6th century Alexandria Egypt a century before it fell to the Muslims) wrote that an object would continue moving through a vacuum.

NO MOTION IN A VACUUM
Avempace (Ibn Bajjah) (1095 – 1138), Averroes (Ibn Rušd) (1126 – 1198) and the Greek slave al-Khazini believed in the theory of Aristotle that an object entering a vacuum would immediately halt because there would be no air to transfer energy to it.
Avicenna (Ibn Sīnā) (980 – 1037) agreed that objects cannot move in a vacuum, but did not explain why.
All of them rejected the correct assertion of 6th Christian theologian John Philoponus that an object would continue moving through a vacuum.

Image by MichaelMaggs, via Wikimedia Commons.
image credit https://en.wikipedia.org/wiki/File:Falling_ball.jpg

 

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