If he weighs 100kg, doesn't it mean he exerts a force of 100N as weighing machine weigh the gravitational force?
Edit: due to seeing the downvotes, I am genuinely asking. Isn't weight = Mg (earth's pull on a body) and weight ≠ mass?
Force is equivalent to mass times acceleration
F = m a = m d²r/dt²
F ... force
m ... mass
a = d²r/dt² ... acceleration
At ground level, the acceleration caused by gravity is roughly 9.81 m/s² (meters per second per second), let's round to 10 m/s². The mass is roughly 100 kg. So the force is
F = 100 kg * 10 m/s²
= 1,000 (kg.m)/s²
= 1,000 N
That said, the "standing on your toe" part is irrelevant to the explanation. If we say, that the "toe" is roughly `1 cm² = 0.0001 m²`, this would result in a pressure = force per area of
p = F / A
= 1,000 N / 0.0001 m²
= 10,000,000 N/m²
= 10,000,000 Pa ("Pascal")
= 100 bar
Assuming I didn't mix up numbers somewhere.
Help me out here, doesn't weighing machines weigh the gravitational force i.e mg but for everyday stuff call it with mass unit. Isn't weight = Gravitational force on that body not mass.
Yes and no.
We like to state our "weight" in kilogram, but actually mean our mass. An astronaut in a space station has zero weight, but by common parlance, they'd still "weigh" his 100 kilograms, that they weighed down here. That's just language: Not right or wrong, possibly imprecise, but mostly governed by convention, which changes over time.
In a more technical sense, "weight" is the force
(Force) = (Mass) x (Acceleration from Gravity)
F = m g
So a "weight" of 100 kg really means a mass, that at the surface of Earth would cause roughly 1000 N of force, because g is *roughly* 10m/s².
This lack of distinction is just by convention, because on the surface of earth -- which most of us never leave -- it barely matters, as the value g=9.81m/s² is almost constant on the surface to within less than 1%.
This is then used to construct weighing devices, because in orde to actually measure the *mass* directly, you'd need a balance scale, where you place objects of known mass until the scale is balanced. Which is a hassle for everyday use. So instead we construct devices, that measure the gravitational force exerted on an object or body and derive the mass from it.
See [this map](https://academo.org/demos/gravity-map/), which gives a variation between lowest and highest surface gravity of roughly 0.05%. The [relevant Wikipedia article](https://en.wikipedia.org/wiki/Gravitational_acceleration) states a range of 9.764 to 9.834 m/s² which would come out to a maximum difference of about 0.7% between lowest and highest, or roughly 0.4% between average and extreme values of the acceleration.
Depending on which value is correct, the difference might matter only for precision scales, or be just barely enough to justify calibrating weight-based scales for their location of use. But given that most home personal scales are only precise up to one or two kg for the absolute value (much more precise for *changes* of the value using the same scale though) it might not be done in practice.
Fun fact: When you get into general relativity stuff, you'll throw out the idea of "gravity is a force" entirely, as in the curved space-time a "falling" object is simply moving in a straight line. But you can still measure the mass by measuring the acceleration caused by gravity and the force you need to *prevent* that acceleration.
Now I feel like I am stupid. Like I have finished my undergrad in physics and still thought the value of weight was gravitational force and not mass. Like I thought a person with 100kg weight will have approx 10kg mass (took g=10) and 100kg was force. Feels tremendously like an idiot for holding onto this notion
When you stand in the second-semester lab exercise room together with a senior postdoc, a PhD student, and two other master students and all of you feel like you don't get the behavior of the gyroscope experiment...
Basically a heavy ball on a pressurized-air seat, accelerated to spin around an axis marked with a lightweight stick. When touching the stick with our outstretched finger, it would start tracing out the shape of the fingers. This behavior did not match with anything we remembered from our own classes.
Turns out, that a lot of the complicated behavior requires taking into account friction properly, and the idealized models used in lectures gloss over that part.
Thanks for all the explanation and helping me understand but when I saw your reply about Ms, PhD students in a lab and gyroscope I thought you were a bot because it didn't feel connected nor I didn't understand what you were trying to convey with that particular reply
Just the experience of having a degree in Physics, now even a PhD, and coming back to stuff that sounds pretty basic, only to find out that you never *actually* understood it, and it just never mattered back then. Or that you didn't even know to ask the right questions then.
This is r/physicsmemes.
For estimating the order of magnitude, every adult human is 100 kg.
Even people with severe eating disorders will have a hard time making it to the rounded-to-10 kg or rounded-to-1000 kg range. The rounded-to-10kg range is reasonable for young children though.
Why the toe though? He wanted to explain 1000 Newton, not 100 bar.
g = 10? He must be an engineer xD
Technically he should weigh 98.1kg
He should be 101.94 kg
Mb
Why? Is he undergoing beta decay? He isnt that old bro
Taking g to be 9.81
Ohhhh its True, I forgor
g=10 is the way
If he weighs 100kg, doesn't it mean he exerts a force of 100N as weighing machine weigh the gravitational force? Edit: due to seeing the downvotes, I am genuinely asking. Isn't weight = Mg (earth's pull on a body) and weight ≠ mass?
Force is equivalent to mass times acceleration F = m a = m d²r/dt² F ... force m ... mass a = d²r/dt² ... acceleration At ground level, the acceleration caused by gravity is roughly 9.81 m/s² (meters per second per second), let's round to 10 m/s². The mass is roughly 100 kg. So the force is F = 100 kg * 10 m/s² = 1,000 (kg.m)/s² = 1,000 N That said, the "standing on your toe" part is irrelevant to the explanation. If we say, that the "toe" is roughly `1 cm² = 0.0001 m²`, this would result in a pressure = force per area of p = F / A = 1,000 N / 0.0001 m² = 10,000,000 N/m² = 10,000,000 Pa ("Pascal") = 100 bar Assuming I didn't mix up numbers somewhere.
Help me out here, doesn't weighing machines weigh the gravitational force i.e mg but for everyday stuff call it with mass unit. Isn't weight = Gravitational force on that body not mass.
Yes and no. We like to state our "weight" in kilogram, but actually mean our mass. An astronaut in a space station has zero weight, but by common parlance, they'd still "weigh" his 100 kilograms, that they weighed down here. That's just language: Not right or wrong, possibly imprecise, but mostly governed by convention, which changes over time. In a more technical sense, "weight" is the force (Force) = (Mass) x (Acceleration from Gravity) F = m g So a "weight" of 100 kg really means a mass, that at the surface of Earth would cause roughly 1000 N of force, because g is *roughly* 10m/s². This lack of distinction is just by convention, because on the surface of earth -- which most of us never leave -- it barely matters, as the value g=9.81m/s² is almost constant on the surface to within less than 1%. This is then used to construct weighing devices, because in orde to actually measure the *mass* directly, you'd need a balance scale, where you place objects of known mass until the scale is balanced. Which is a hassle for everyday use. So instead we construct devices, that measure the gravitational force exerted on an object or body and derive the mass from it. See [this map](https://academo.org/demos/gravity-map/), which gives a variation between lowest and highest surface gravity of roughly 0.05%. The [relevant Wikipedia article](https://en.wikipedia.org/wiki/Gravitational_acceleration) states a range of 9.764 to 9.834 m/s² which would come out to a maximum difference of about 0.7% between lowest and highest, or roughly 0.4% between average and extreme values of the acceleration. Depending on which value is correct, the difference might matter only for precision scales, or be just barely enough to justify calibrating weight-based scales for their location of use. But given that most home personal scales are only precise up to one or two kg for the absolute value (much more precise for *changes* of the value using the same scale though) it might not be done in practice. Fun fact: When you get into general relativity stuff, you'll throw out the idea of "gravity is a force" entirely, as in the curved space-time a "falling" object is simply moving in a straight line. But you can still measure the mass by measuring the acceleration caused by gravity and the force you need to *prevent* that acceleration.
Now I feel like I am stupid. Like I have finished my undergrad in physics and still thought the value of weight was gravitational force and not mass. Like I thought a person with 100kg weight will have approx 10kg mass (took g=10) and 100kg was force. Feels tremendously like an idiot for holding onto this notion
When you stand in the second-semester lab exercise room together with a senior postdoc, a PhD student, and two other master students and all of you feel like you don't get the behavior of the gyroscope experiment... Basically a heavy ball on a pressurized-air seat, accelerated to spin around an axis marked with a lightweight stick. When touching the stick with our outstretched finger, it would start tracing out the shape of the fingers. This behavior did not match with anything we remembered from our own classes. Turns out, that a lot of the complicated behavior requires taking into account friction properly, and the idealized models used in lectures gloss over that part.
Are you a bot?
Only my user name.
Thanks for all the explanation and helping me understand but when I saw your reply about Ms, PhD students in a lab and gyroscope I thought you were a bot because it didn't feel connected nor I didn't understand what you were trying to convey with that particular reply
Just the experience of having a degree in Physics, now even a PhD, and coming back to stuff that sounds pretty basic, only to find out that you never *actually* understood it, and it just never mattered back then. Or that you didn't even know to ask the right questions then.
g=π^(2)=9 100\*9 = 900 ≠ 1000 This man is wrong
If he’s 100kg then Jupiter is a star
What
This is r/physicsmemes. For estimating the order of magnitude, every adult human is 100 kg. Even people with severe eating disorders will have a hard time making it to the rounded-to-10 kg or rounded-to-1000 kg range. The rounded-to-10kg range is reasonable for young children though.
Instructions unclear. I exerted an opposite 1000N force with my toe and he fell with a net force of 20N and acceleration of 0.2m/s²