Free fall and the equivalence principle revisited
(2017) In Physics Education 52(6). Abstract
Free fall is commonly discussed as an example of the equivalence principle, in the context of a homogeneous gravitational field, which is a reasonable approximation for small test masses falling moderate distances. Newton's law of gravity provides a generalisation to larger distances, and also brings in an inhomogeneity in the gravitational field. In addition, Newton's third law of action and reaction causes the Earth to accelerate towards the falling object, bringing in a mass dependence in the time required for an object to reach ground  in spite of the equivalence between inertial and gravitational mass. These aspects are rarely discussed in textbooks when the motion of everyday objects are discussed. Although these effects are... (More)
Free fall is commonly discussed as an example of the equivalence principle, in the context of a homogeneous gravitational field, which is a reasonable approximation for small test masses falling moderate distances. Newton's law of gravity provides a generalisation to larger distances, and also brings in an inhomogeneity in the gravitational field. In addition, Newton's third law of action and reaction causes the Earth to accelerate towards the falling object, bringing in a mass dependence in the time required for an object to reach ground  in spite of the equivalence between inertial and gravitational mass. These aspects are rarely discussed in textbooks when the motion of everyday objects are discussed. Although these effects are extremely small, it may still be important for teachers to make assumptions and approximations explicit, to be aware of small corrections, and also to be prepared to estimate their size. Even if the corrections are not part of regular teaching, some students may reflect on them, and their questions deserve to be taken seriously.
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 author
 Pendrill, Ann Marie ^{LU}
 organization
 publishing date
 20171101
 type
 Contribution to journal
 publication status
 published
 subject
 in
 Physics Education
 volume
 52
 issue
 6
 publisher
 IOP Publishing
 external identifiers

 scopus:85032223161
 ISSN
 00319120
 DOI
 10.1088/13616552/aa5e38
 language
 English
 LU publication?
 yes
 id
 ed4efdff9ffa46288cfdfeea6e4dfe55
 date added to LUP
 20171107 12:39:58
 date last changed
 20180114 04:36:49
@article{ed4efdff9ffa46288cfdfeea6e4dfe55, abstract = {<p>Free fall is commonly discussed as an example of the equivalence principle, in the context of a homogeneous gravitational field, which is a reasonable approximation for small test masses falling moderate distances. Newton's law of gravity provides a generalisation to larger distances, and also brings in an inhomogeneity in the gravitational field. In addition, Newton's third law of action and reaction causes the Earth to accelerate towards the falling object, bringing in a mass dependence in the time required for an object to reach ground  in spite of the equivalence between inertial and gravitational mass. These aspects are rarely discussed in textbooks when the motion of everyday objects are discussed. Although these effects are extremely small, it may still be important for teachers to make assumptions and approximations explicit, to be aware of small corrections, and also to be prepared to estimate their size. Even if the corrections are not part of regular teaching, some students may reflect on them, and their questions deserve to be taken seriously.</p>}, articleno = {065002}, author = {Pendrill, Ann Marie}, issn = {00319120}, language = {eng}, month = {11}, number = {6}, publisher = {IOP Publishing}, series = {Physics Education}, title = {Free fall and the equivalence principle revisited}, url = {http://dx.doi.org/10.1088/13616552/aa5e38}, volume = {52}, year = {2017}, }