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High school shit

Anonymous Mon 21 Mar 21:54:48 2022 No.14323803 View Reply Original Report

Quoted By: >>14323815 >>14323823 >>14323841 >>14323862 >>14324167 >>14324201 >>14325046

I've been studying physics for who knows how long. Still, whenever I open a high school physics book I find exercises that make me scratch my head. And it's always Newtonian mechanics. I've clearly skipped that part when I was in high school.

I realized I'm probably too dumb to study physics. However, instead of giving up and finding something easier, I picked up the high school text book and decided to force myself to understand the parts that give me trouble.

Currently wondering what the fuck happens when you stand on a scale as an elevator goes down and decelerates. The scale now shows a larger number. Let's say you weigh 62,0 kg, now the scale says 74,3 kg. What's the acceleration of the elevator? My reasoning is in pic related.

Anonymous

Anonymous Mon 21 Mar 2022 21:59:23 No.14323815 Report

Quoted By:

>>14323803
>What's the acceleration of the elevator?
?v/?t

Anonymous

Anonymous Mon 21 Mar 2022 22:04:25 No.14323823 Report

Quoted By:

>>14323803
Can you post the original question instead of your take on it?

The elevator decelerates because of the braking force. The accelerations depend on how quickly the braking happens.

As the elevator is moving down, your weight will read lower. It's a mystery.

Anonymous

Anonymous Mon 21 Mar 2022 22:13:29 No.14323841 Report

Quoted By: >>14323843

>>14323803
try and piece it together from these questions:

what forces typically pull you towards the earth?

what would a scale read if there was no gravity?

what does the scale manufacturer assume is constant in the equation f = ma?

give a name to the variables m and a in the equation f = ma.

if the weight of a person on a scale doubled, what variable in f = ma would also have to double?

which would produce a larger force, being hit with a 1kg ball going 10 m/s, or being hit with a 2kg ball going 5m/s?

which would produce a larger force, a 120kg person going 9.8m/s, or a 60kg person going 19.6m/s?

Anonymous

Anonymous Mon 21 Mar 2022 22:14:54 No.14323843 Report

Quoted By:

>>14323841
i'm not a teacher, don't let yourself get stuck on any of these questions because i phrased them poorly. they should be pretty intuitive, like a minute each.

Anonymous

Anonymous Mon 21 Mar 2022 22:25:22 No.14323862 Report

Quoted By:

>>14323803
If you're driving a bus, and the bus suddenly brakes, how do the pasengers inside react?
Because of inertia, the body wants to stay at constant speed, but is being affected because the shell the body is inside is accelerating.

Anonymous

Anonymous Mon 21 Mar 2022 22:49:24 No.14323918 Report

Quoted By: >>14323959

>Inside an elevator you feel heavier, lighter, or normal depending on the motion of the elevator. In fact what you feel as your weight is your apparent weight, that is not always the same as your actual weight (or simply your weight). In this article you will find the definition of apparent weight and actual weight.

The hell is apparent weight.

Anonymous

Anonymous Mon 21 Mar 2022 23:15:57 No.14323959 Report

Quoted By:

>>14323918
Normal force

Anonymous

Anonymous Tue 22 Mar 2022 00:58:42 No.14324167 Report

Quoted By:

>>14323803
> I've been studying physics for who knows how

What the fuck do you study where you can understand something advanced without Newtonian mechanics being intuitive.

Anonymous

Anonymous Tue 22 Mar 2022 01:16:11 No.14324201 Report

Quoted By: >>14325084 >>14325310

>>14323803
OP, I laud you for attempting the problem, and neatly organizing your uncertainty. For that, I'll reward you with an answer.

An interesting approach. But you really should start with Newton's Second Law.

$F_{net} = ma$

When anon is stationary, we have

$N_{anon} - G_{anon} = 0$

Can you see why? Now, when the elevator is decelerating, as you've correctly noted, the acceleration is upward.

$N_{2,anon} - G_{anon} = ma$

Again, can you see where this comes from? The scale measures N, not G. Therefore, symbolically, we have

$m_{measured}g - mg = ma$

Or,

$a = \frac{m_{measured}g - mg}{m} = \frac{(\Delta m) g}{m}$

which matches what you observed: the acceleration is merely the difference in apparent mass. But you've stumbled upon it by accident---you should generally be more careful with setting up Newton's Second Law.

As for your car example, that's an astute observation. The box doesn't move relative to the car, otherwise it would fall off. However, the box must also be accelerating since it's part of the truck-box system. Which force must exist to cause this acceleration? (Friction)

If you draw the net force acting on the box relative to the car, you'd observe that's zero.

Anonymous

Anonymous Tue 22 Mar 2022 09:12:36 No.14325046 Report

Quoted By: >>14325055

>>14323803
Fuck off with your little stories. You just want us to do your homework because you know there are many sorry saps here who will do it for you. In their minds they are doing this for clout, but to everyone else you can see they are getting used.

Anonymous

Anonymous Tue 22 Mar 2022 09:18:51 No.14325055 Report

Quoted By:

>>14325046
>Fuck off with your little stories. You just want us to do your homework

Believe it or not, I'm a university student. These are high school problems, which are not my homework.
I genuinely struggle with the basics so secretly I get high school textbooks and practice at home.

Anonymous

Anonymous Tue 22 Mar 2022 09:34:17 No.14325084 Report

Quoted By:

>>14324201
Thank you. I used to have a friend who was high IQ and he could just intuitively solve all of these in his head. He didn't make any methodical equations or calculations, he just knew what would happen in that situation.
I always criticized his intuitive approach because it's not scientific to me, but because it was impressive, I sort of tried to follow the same path until I realized all the textbooks recommend you do it methodically and mathematically starting from F_net = m*a.

Another huge problem I have is that I have near photographic memory. In high school I never learned to think because I could memorize the solutions to the problems and simply print them on paper in the test. Part of me believed that I had understood what I had read. But after a couple of years I was in uni and realized that I hadn't understood anything at all. This was a humbling realization.

Anonymous

Anonymous Tue 22 Mar 2022 12:00:54 No.14325310 Report

Quoted By: >>14325333

>>14324201
What happens in a fighter jet when I experience several G's?
Does it simply mean that the normal force of the seat is pushing me turbo hard but my actual weight (G) is still 1 G?

Anonymous

Anonymous Tue 22 Mar 2022 12:13:50 No.14325333 Report

Quoted By:

>>14325310
Yes

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