I need the definition of a few basic physics terms. Can anyone help?

  • Thread starter syohannan
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  • #1
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So, I know this stuff is probably very elementary for most of the people on this site, but I have never had physics before, and I just started physics I at college. The professor has asked us to learn a few basic physics terms and I am having a hard time finding clear definitions for some of them.

These are what I need defined:

object
particle
body
extended body
rigid body


Thanks!
 

Answers and Replies

  • #2
tiny-tim
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welcome to pf!

hi syohannan! welcome to pf! :wink:
object
particle
body
extended body
rigid body
have you tried wikipedia?

anyway, tell us what you think each one means :smile:
 
  • #3
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Yes, I have looked at several website as well as Wikipedia, and I am having a hard time finding clearly defined definitions for some of these.

I have found some of them, but I am still not confident that they are they best definitions, since I have seen several different ones for a few of these. Here is what I have found.

object = anything that has shape, but my teacher said anything that can move? This is why I am unsure.

particle = an inextricable piece of mass (this one I am OK with, unless you have something better. This is why I asked)

body = a mass of unspecified size and shape (but i have seen other sites that say, a body and an object are the same thing)

extended body (this one specifically I can not find a definition for at all)

rigid body = object with mass that has a very specific size and shape (this is my teacher's definition, but I have seen others that vary)

Can anyone please give me some clearly defined definitions for these, thanks
 
  • #4
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The concept of a rigid body is an interesting one for a beginner in that it can swiftly lead you to realize that it is an assumption that does not hold in the real world.
Rigid body = an object that does not bend at all e.g. a rigid bar supported at one end has no deflection in the earth's gravitational field.
When I taught mechanics years ago we started with Statics i.e. the behaviour of material bodies with no motion. After some time on the subject, with the students confident of their prowess I would set the following three problems for homework then discussion:
A) a rigid bar, length x, mass m supported at it's mid point - what is the reaction at the support.
B) similar bar, supported at two points - what are the reactions at the supports (at various times I would specify different positions for the supports)
C) similar bar, supported at three pints - what are the reactions.

A & B they should solve easily, C gives a good discussion of what assumptions we make in trying to solve problems in the real world AND WHEN THOSE ASSUMPTIONS CEASE TO HOLD.
 
  • #5
particle = an inextricable piece of mass (this one I am OK with, unless you have something better. This is why I asked)
A particle need not have mass. Photons are particles, and they are massless. With that in mind, can you take another stab at it?
 
  • #6
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AND WHEN THOSE ASSUMPTIONS CEASE TO HOLD.
In my case it's usually about the three pint point.:biggrin:
Sorry I could not resist.
 
  • #7
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Yes, I have looked at several website as well as Wikipedia, and I am having a hard time finding clearly defined definitions for some of these.

I have found some of them, but I am still not confident that they are they best definitions, since I have seen several different ones for a few of these. Here is what I have found.

object = anything that has shape, but my teacher said anything that can move? This is why I am unsure.

particle = an inextricable piece of mass (this one I am OK with, unless you have something better. This is why I asked)

body = a mass of unspecified size and shape (but i have seen other sites that say, a body and an object are the same thing)

extended body (this one specifically I can not find a definition for at all)

rigid body = object with mass that has a very specific size and shape (this is my teacher's definition, but I have seen others that vary)

Can anyone please give me some clearly defined definitions for these, thanks
Partly right, partly wrong. Object in physics means pretty much the same as what it means in daily life. body normally means a solid (not liquid or gas), extended body or extended object - this is used to distinguish from 'point' object which are objects whose entire mass and extent is concentrated in one point( which occupy just one point literally) and anything which is not a point object is an extended object. rigid body - cannot be deformed - the distance between any two points on a rigid body cannot change. particle normally means a point mass, i.e. an object whose entire mass and extent is concentrated at one point. (in particle physics it has a slightly different meaning, there it means fundamental particle)
 
  • #8
Fredrik
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I like the following description of a classical point particle: It's an object whose motion can be described by a single curve in spacetime.
 

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