Comments on: Random act of science teaching – you weigh less on the way down in the an elevator http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/ Talk Like A Physicist Day : March 14, 2011 Wed, 05 Oct 2011 20:51:18 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: Troll http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-5074 Troll Tue, 26 Jan 2010 00:00:20 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-5074 lol what a bunch of nerdz lol what a bunch of nerdz

]]> By: Joe http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4916 Joe Sun, 17 May 2009 23:10:42 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4916 Agreed, "what does it matter". Stumbled this conversation, and (unfortunately) I have to cast my vote for Mr. Physics. Though stuck-up, he is correct about both the definition of weight and the fact that your weight does not significantly (your weight may increase slightly as you move closer to Earth) change in an elevator. Agreed, “what does it matter”.

Stumbled this conversation, and (unfortunately) I have to cast my vote for Mr. Physics. Though stuck-up, he is correct about both the definition of weight and the fact that your weight does not significantly (your weight may increase slightly as you move closer to Earth) change in an elevator.

]]> By: what does it matter http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4884 what does it matter Sun, 26 Apr 2009 00:47:11 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4884 what does it matter, you are an obese american no matter what your scale tells you!! what does it matter, you are an obese american no matter what your scale tells you!!

]]> By: Darjeed http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4882 Darjeed Sat, 25 Apr 2009 03:12:26 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4882 Acceleration has nothing to do with it, all of you have been out of school for to long the weight of an object is the magnitude, W, of the force that must be applied to an object in order to support it (i.e. hold it at rest) in a gravitational field. If you are slowly moving downward The forces pushing up from the elevator are less than the force needed to keep you at rest. example if you weigh 170 lbs and are moving downwards then we know the elevator isn't pushing you upwards with 170 lbs of force. it is pushing with a number < 170 lbs which would be measured by a weight scale as a drop in weight since you are falling and if you are going up; Again with an acceleration of 0 but velocity of any number the floor is pushing up on you at a force greater than 170 lbs making you rise against the gravitational pull. it's all in the definition please refresh your memories of basic equations, you might build or work on something I could be injured by =( (( Kept it simple )) ( Acceleration has nothing to do with it, all of you have been out of school for to long

the weight of an object is the magnitude, W, of the force that must be applied to an object in order to support it (i.e. hold it at rest) in a gravitational field.

If you are slowly moving downward The forces pushing up from the elevator are less than the force needed to keep you at rest. example if you weigh 170 lbs and are moving downwards then we know the elevator isn’t pushing you upwards with 170 lbs of force. it is pushing with a number < 170 lbs which would be measured by a weight scale as a drop in weight since you are falling and if you are going up; Again with an acceleration of 0 but velocity of any number the floor is pushing up on you at a force greater than 170 lbs making you rise against the gravitational pull. it’s all in the definition please refresh your memories of basic equations, you might build or work on something I could be injured by =(

(( Kept it simple ))

(

]]> By: James http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4870 James Tue, 14 Apr 2009 01:27:16 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4870 mass and weight are two different things. mass and weight are two different things.

]]> By: andy http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4855 andy Fri, 03 Apr 2009 15:06:38 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4855 What do you guys think, is it a Miata or a Del Sol? What do you guys think, is it a Miata or a Del Sol?

]]> By: the baldchemist http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4850 the baldchemist Mon, 30 Mar 2009 09:54:27 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4850 E =mc2 Any way you look at it. You even weigh more on the way up. E =mc2
Any way you look at it. You even weigh more on the way up.

]]> By: John http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4711 John Mon, 19 Jan 2009 08:48:07 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4711 It's not true that a person weighs less when coming down an elevator than when going up. You weigh less at the BEGINNING of a trip down than at the BEGINNING of a trip up,and MORE at the end of a trip down than at the end of a trip up. At the beginning of a trip down, the elevator is ACCELERATING downward. Soon it reaches a steady speed, and your weight becomes normal. Then it DECELERATES downward (which is the same as accelerating upward) as it comes to a stop at the final floor. Likewise, when going up the elevator first accelerates upward, then reaches a steady speed upward, and finally decelerates to a stop. If you stand on a scale in an elevator, there are two forces acting on you: the downward force of gravity, which is constant (for the purposes of this discussion), and the upward force of the scale on your feet. When you are stationary or when you are moving at a constant speed, these forces are equal and opposite and the scale shows your correct weight. But when you are accelerating up or down, the effect of that acceleration changes the net force and the scale shows a different weight. Net force is calculated by mass (your actual weight) times acceleration and is written as 'ma'. Thus, to pick one case, at the beginning of a trip up in the elevator, you are accelerating upward with acceleration "a". The vertical force equation is N - mg = ma where N is the upward normal force of the scale and -mg is the downward gravitational force. We can solve for N: N - mg = ma N = mg + ma N = m(g + a) The scale measures the force N, dividing it by g (gravity) to read in units of mass (pounds in this example): N/g = m(g + a)/g = m(1 + a/g) = m + ma/g You can see that the scale reads higher than your normal "weight" m because "a" is positive (m and g are always positive). On the other hand, at the beginning of a trip down in the elevator, the scale reads lower than your normal "weight" because "a" is negative (accelerating downward). It’s not true that a person weighs less when coming down an elevator than when going up. You weigh less at the BEGINNING of a trip down than at the BEGINNING of a trip up,and MORE at the end of a trip down than at the end of a trip up.

At the beginning of a trip down, the elevator is ACCELERATING
downward. Soon it reaches a steady speed, and your weight becomes normal. Then it DECELERATES downward (which is the same as accelerating upward) as it comes to a stop at the final floor. Likewise, when going up the elevator first accelerates upward, then reaches a steady speed upward, and finally decelerates to a stop.

If you stand on a scale in an elevator, there are two forces acting on you: the downward force of gravity, which is constant (for the purposes of this discussion), and the upward force of the scale on your feet.

When you are stationary or when you are moving at a constant speed, these forces are equal and opposite and the scale shows your correct weight. But when you are accelerating up or down, the effect of that acceleration changes the net force and the scale shows a different weight.

Net force is calculated by mass (your actual weight) times
acceleration and is written as ‘ma’.

Thus, to pick one case, at the beginning of a trip up in the elevator, you are accelerating upward with acceleration “a”. The vertical force equation is

N – mg = ma

where N is the upward normal force of the scale and -mg is the downward gravitational force. We can solve for N:

N – mg = ma
N = mg + ma
N = m(g + a)

The scale measures the force N, dividing it by g (gravity) to read in units of mass (pounds in this example):

N/g = m(g + a)/g = m(1 + a/g) = m + ma/g

You can see that the scale reads higher than your normal “weight” m because “a” is positive (m and g are always positive). On the other hand, at the beginning of a trip down in the elevator, the scale reads lower than your normal “weight” because “a” is negative (accelerating downward).

]]> By: Josh http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4710 Josh Sat, 17 Jan 2009 23:49:22 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4710 Hey, this is from Science World, in BC, Canada! I used to love going there on field trips and such, the ball tower is so cool! I <3 contraptions! Hey, this is from Science World, in BC, Canada!
I used to love going there on field trips and such, the ball tower is so cool! I <3 contraptions!

]]> By: little bunny foo foo http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4705 little bunny foo foo Fri, 16 Jan 2009 01:34:12 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4705 you weigh less on the way up because the force of gravity on your body is dependent upon the distance between you and the center of the earth. The closer you are to the center of the earth the more you weigh. you weigh less on the way up because the force of gravity on your body is dependent upon the distance between you and the center of the earth. The closer you are to the center of the earth the more you weigh.

]]> By: Trifon http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4702 Trifon Tue, 13 Jan 2009 12:09:20 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4702 This whole is a "strange" effect of the Newtonian mechanics. When you try to "measure" a force, weigth of an object in our case, you have to take into the account the observer in the calculations. If the one that makes the observation is the one in the elevator he will see his weight change, due to the fact that because he is moving alongside with the frame of reference you only can perceive that the acceleration of gravity [g] changes (because of the elevator's acceleration, but nevertheless you cannot discriminate between this change and an actual change in g). If the observation had been made from the outside of the elevator, therefore using the newtonian inertial frame of reference the count of your weight would have been the same. This whole problem is widely known in mechanics as the problem of the elevator (or something like this...!) and it is used to make clear that there is no difference between the weight of an object because of acceleration and the weight of the object because of gravity. It was also one of the problems that led to the improvement of the Newtonian mechanics by Lorentz. This whole is a “strange” effect of the Newtonian mechanics. When you try to “measure” a force, weigth of an object in our case, you have to take into the account the observer in the calculations. If the one that makes the observation is the one in the elevator he will see his weight change, due to the fact that because he is moving alongside with the frame of reference you only can perceive that the acceleration of gravity [g] changes (because of the elevator’s acceleration, but nevertheless you cannot discriminate between this change and an actual change in g). If the observation had been made from the outside of the elevator, therefore using the newtonian inertial frame of reference the count of your weight would have been the same.
This whole problem is widely known in mechanics as the problem of the elevator (or something like this…!) and it is used to make clear that there is no difference between the weight of an object because of acceleration and the weight of the object because of gravity. It was also one of the problems that led to the improvement of the Newtonian mechanics by Lorentz.

]]> By: Connor http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4700 Connor Sun, 11 Jan 2009 22:01:02 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4700 *EDIT to previous post: I meant to say "the forces exerted on you WILL be greater or smaller depending on whether the acceleration is positive or negative" *EDIT to previous post: I meant to say “the forces exerted on you WILL be greater or smaller depending on whether the acceleration is positive or negative”

]]> By: Connor http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4699 Connor Sun, 11 Jan 2009 21:59:28 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4699 @ Zack, I don't think anyone said your mass would change, they were arguing as to whether or not your weight changes due to the movement of the lift. I would be inclined to say that, yes, your weight does change, but only as the lift is accelerating. When the speed of the lift is constant, the normal force exerted on you by the lift floor will remain constant and so therefore your weight will remain constant, as weight is a resultant of the normal force exerted on you by the surface you are standing on. However as the lift is accelerating the forces exerted on you will not be greater or smaller depending on whether the acceleration is positive or negative and that in turn will change the normal force exerted on you and so therefore your weight will not be the same. @ Zack, I don’t think anyone said your mass would change, they were arguing as to whether or not your weight changes due to the movement of the lift.

I would be inclined to say that, yes, your weight does change, but only as the lift is accelerating. When the speed of the lift is constant, the normal force exerted on you by the lift floor will remain constant and so therefore your weight will remain constant, as weight is a resultant of the normal force exerted on you by the surface you are standing on.

However as the lift is accelerating the forces exerted on you will not be greater or smaller depending on whether the acceleration is positive or negative and that in turn will change the normal force exerted on you and so therefore your weight will not be the same.

]]> By: A different Zak http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4698 A different Zak Sun, 11 Jan 2009 20:23:23 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4698 Other Zack is right. Mr. Physics gave a semantic argument which is equivalent to the original argument. Rest mass is an intrinsic property of an object. The observed force acted on you by the ground (commonly called weight) is dependent on how you are accelerating. Hence, your weight changes as the elevator moves. Mr. Physics is a perfect example of why people who don't think with math can never really understand physics. Other Zack is right. Mr. Physics gave a semantic argument which is equivalent to the original argument. Rest mass is an intrinsic property of an object. The observed force acted on you by the ground (commonly called weight) is dependent on how you are accelerating. Hence, your weight changes as the elevator moves.

Mr. Physics is a perfect example of why people who don’t think with math can never really understand physics.

]]> By: Zack http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4697 Zack Sun, 11 Jan 2009 07:16:25 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4697 People please, mass is constant, even on the moon your mass is the same as it is on Earth. What is variable is your weight. Your weight changes as the elevator accelerates up and down the shaft. Ok? (Physics major in University for your information) People please, mass is constant, even on the moon your mass is the same as it is on Earth. What is variable is your weight. Your weight changes as the elevator accelerates up and down the shaft. Ok? (Physics major in University for your information)

]]> By: Peter http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4696 Peter Sat, 10 Jan 2009 23:04:44 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4696 Its still wrong, chrispopher...... I would argue that your weight does change. Becuase if you are going down, you are by definition getting closer to the center of the earth. We all now gravity is apporxiamtly proportinal to the square of the distance between the objects.... So if we are getting close, gravity is excerting a deffernt acceleration on us, thus our weight changes. Maybe by inly a litte, but none the less. And for the record, weight is a mesurement of the gravitaional force (yes, force) acting on an object. Not any old force, but gravity. So unless the lift screws with gravity in some way, it does not change your weight. Mr physics fails fails Its still wrong, chrispopher……

I would argue that your weight does change.

Becuase if you are going down, you are by definition getting closer to the center of the earth.
We all now gravity is apporxiamtly proportinal to the square of the distance between the objects….
So if we are getting close, gravity is excerting a deffernt acceleration on us, thus our weight changes.
Maybe by inly a litte, but none the less.

And for the record, weight is a mesurement of the gravitaional force (yes, force) acting on an object.
Not any old force, but gravity.

So unless the lift screws with gravity in some way, it does not change your weight.

Mr physics fails fails

]]> By: Christopher http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/comment-page-1/#comment-4675 Christopher Sat, 13 Dec 2008 20:15:03 +0000 http://talklikeaphysicist.com/2008/random-act-of-science-teaching-you-weigh-less-on-the-way-down-in-the-an-elevator/#comment-4675 Ooo wow everyone, look how intelligent I am. I took a high school physics course and as such I can nitpick this article like a pedant, instead of remarking on the point of the scale, which is to encourage scientific interest and learning. Which is something a brilliant internet physicist such as yourself should appreciate. Ooo wow everyone, look how intelligent I am. I took a high school physics course and as such I can nitpick this article like a pedant, instead of remarking on the point of the scale, which is to encourage scientific interest and learning. Which is something a brilliant internet physicist such as yourself should appreciate.

]]>