AndrewC

497 reputation

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	location	United Kingdom
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visits	member for	5 months
	seen	Jan 24 at 16:02
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Hobby programmer, ex Computing teacher.

	497 reputation	bio	website		visits	member for	5 months
28 badges		location	United Kingdom		seen	Jan 24 at 16:02

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Dec 4	awarded	Constituent
Dec 4	awarded	Caucus
Dec 3	awarded	Good Answer
Dec 2	comment	With Newton's third law, why are things capable of moving? A nice exercise is to draw the table, matchbox, person and earth and find as many third law matched pairs you can (remember to make sure they're acting on different objects). There's an answer to be found in the revision history of my answer (click the link after the word edited), but I hid it because I feel it distracts from the main part of the answer.
Dec 2	revised	With Newton's third law, why are things capable of moving? The additional diagram didn't add anything, and I felt it was distracting from the main point.
Dec 2	comment	With Newton's third law, why are things capable of moving? @JavierBadia Fixed now. Thanks for pointing out my silly (and ironic) but key mistake. My answer is better now because of your comment.
Dec 2	revised	With Newton's third law, why are things capable of moving? better diagram correcting silly error, additional over-the-top diagram for fun
Dec 2	awarded	Mortarboard
Dec 2	awarded	Critic
Dec 2	comment	With Newton's third law, why are things capable of moving? @StevenLu because I found it funny, particularly "May cause fire.".
Dec 2	revised	With Newton's third law, why are things capable of moving? blue forces are equal by first law!
Dec 2	awarded	Nice Answer
Dec 2	answered	With Newton's third law, why are things capable of moving?
Nov 30	comment	Why is a book on a table not an example of Newton's third law? The weight of the book does not act on the table, it acts on the earth and the book. The force on the table due to the book is a normal force, not a weight force, (just as the force on the book due to the table is not, as you say). Neither of these reaction forces are directly due to gravity, both of them are equal to the weight of the book only because of equilibrium; saying one is and the other isn't isn't true, and these normal forces can never be different to each other precisely because of Newton's third law.
Nov 29	answered	How do I know the position of some mass in space (starting at rest) over time when applying earth's gravitational force to it?
Nov 29	comment	Why is a book on a table not an example of Newton's third law? I thought you were making an interesting point in distinguishing weight force from gravitational force (perhaps about the discrepency between $g=9.81m/s^2$ and $Gm_E/r_E^2$ in practice) but actually I think you were just making a mistake. Weight is the force due to gravity in the sense you're using it in your answer, calling the distinction important is misleading in this context.
Nov 29	comment	Why is a book on a table not an example of Newton's third law? My point is that your last paragraph sounds like it's talking about Newton's third law by using the phrase equal and opposite, but you're actually using Newton's first law. That's exactly the confusion the textbook was trying to avoid and the question is trying to unpick, so it's unhelpful in this context.
Nov 28	comment	Why is a book on a table not an example of Newton's third law? Would you like to explain your interesting statement about Weight force not being gravitational force?
Nov 28	comment	Why is a book on a table not an example of Newton's third law? Nonono, the "if the table didn't exert an equal and opposite force" argument is Newton's first law. If that's what Newton's third law said (every action has an equal and opposite reaction), it would mean nothing ever moved! My trailer exerts an equal and opposite tension force on my car, even when I'm accelerating.
Nov 28	awarded	Editor