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Free fall and the equivalence principle revisited

Pendrill, Ann Marie LU (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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Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physics Education
volume
52
issue
6
publisher
IOP Publishing
external identifiers
  • scopus:85032223161
ISSN
0031-9120
DOI
10.1088/1361-6552/aa5e38
language
English
LU publication?
yes
id
ed4efdff-9ffa-4628-8cfd-feea6e4dfe55
date added to LUP
2017-11-07 12:39:58
date last changed
2018-01-14 04:36:49
@article{ed4efdff-9ffa-4628-8cfd-feea6e4dfe55,
  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         = {0031-9120},
  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/10.1088/1361-6552/aa5e38},
  volume       = {52},
  year         = {2017},
}