4 ms·

Assuming you're standing on the surface of the earth, that's wrong: You're being accelerated upwards, not downwards. Cf the introductory paragraph and "Physical

by cygx 5y ago

Assuming you're standing on the surface of the earth, that's wrong: You're being accelerated upwards, not downwards. Cf the introductory paragraph and "Physical principles" section of https://en.wikipedia.org/wiki/Accelerometer https://en.wikipedia.org/wiki/Accelerometer

dilippkumar 5y ago
Sorry, I interpreted the - sign in the opposite direction. Either ways, the accelerometer is registering something. If gravity was purely a ‘pseudo force’ as GGP said, I should’ve expected a 0 reading. Am I misunderstanding the point made about the accelerometer?
- cygx 5y ago
  You're at rest relative to Earth's surface. From the perspective of that particular frame, the gravitational (pseudo-)force gets balanced by the normal force. But the gravitational force is 'actually' zero, leaving the normal force accelerating you upwards to be measured by your accelerometer.
  - zackees 5y ago
    The gravitational force is zero, but it balances out with a real force which is not zero?
  - deleted 5y ago
    [deleted]
- roywiggins 5y ago
  The feeling you have of force is due to resting on something that's holding you up. If you take that away, you would be in the same gravitational field but feel no forces on you and your accelerometer would measure 0m/s/s. If you jump off a bridge, during your brief flight you could look at your accelerometer and see zero. The gravitational influence on you hasn't changed at all by jumping off a bridge- the only change was removing the upward force that stopped you from falling.
  - o-__-o 5y ago
    Or record your screen and drop your phone from a second floor balcony to see what the accelerometer reads
kazinator 5y ago
If you're standing, you're not accelerating anywhere. Acceleration is a change in velocity, which is a change in position. The forces on you are balanced: the force of gravity is balanced by the force exerted upon you by the ground. You're not going anywhere, and therefore you're not accelerating. An accelerometer works by comparing the difference between some mass that is acted upon by an external force and a related mass that is loosely connected to it (e.g. by a spring-like linkage. whose strain we can measure) as not to be acted upon by that force directly. If you move the casing of an accelerometer, the sprung mass inside it lags behind, and thereby the acceleration can be measured via strain gauges or whatever. Gravity defies accelerometers because, unsurprisingly, gravity acts on all of the the masses contained in an object equally. (At least any gravitational field you are likely to encounter in ordinary experience is going be almost perfectly uniform across an everyday object.) It is when you are in free-fall, that is when you're accelerating due to gravity. And that's exactly when the accelerometer doesn't tell you anything, because every part of the object is in the same free-fall; all of you is accelerating. The accelerometer is differential. It doesn't see a difference, so it doesn't see acceleration. You now that free-fall is acceleration because orbiting satellites are in free fall and they follow circular paths. Objects will not move in a circle unless a force accelerates them toward the center. Like when you spin a mass on the end of as string, it goes in a circle due to the centripetal force exerted by the tension carried in the string. When you're standing on the planet, your accelerometer is lying to you. Gravity is acting on the sprung mass inside the accelerometer, and it's also acting on the case which holds that mass. But the case is constrained from moving, whereas the sprung mass isn't. So a differential strain develops, which "looks and feels" like acceleration. In summary, an accelerometer is an instrument which measures the acceleration due to a force which is applied just to its casing, and not to some critical piece of mass held inside. Gravity causes equal acceleration of the casing and that piece of mass, and so gravitational acceleration is immeasurable by that accelerometer. Acceleration can be measured with regard to some frame of reference via distance and time calculations.

by cygx 5y ago

dilippkumar 5y ago

Sorry, I interpreted the - sign in the opposite direction. Either ways, the accelerometer is registering something. If gravity was purely a ‘pseudo force’ as GGP said, I should’ve expected a 0 reading. Am I misunderstanding the point made about the accelerometer?

cygx 5y ago
You're at rest relative to Earth's surface. From the perspective of that particular frame, the gravitational (pseudo-)force gets balanced by the normal force. But the gravitational force is 'actually' zero, leaving the normal force accelerating you upwards to be measured by your accelerometer.
- zackees 5y ago
  The gravitational force is zero, but it balances out with a real force which is not zero?
- deleted 5y ago
  [deleted]
roywiggins 5y ago
The feeling you have of force is due to resting on something that's holding you up. If you take that away, you would be in the same gravitational field but feel no forces on you and your accelerometer would measure 0m/s/s. If you jump off a bridge, during your brief flight you could look at your accelerometer and see zero. The gravitational influence on you hasn't changed at all by jumping off a bridge- the only change was removing the upward force that stopped you from falling.
- o-__-o 5y ago
  Or record your screen and drop your phone from a second floor balcony to see what the accelerometer reads

kazinator 5y ago

If you're standing, you're not accelerating anywhere. Acceleration is a change in velocity, which is a change in position. The forces on you are balanced: the force of gravity is balanced by the force exerted upon you by the ground. You're not going anywhere, and therefore you're not accelerating. An accelerometer works by comparing the difference between some mass that is acted upon by an external force and a related mass that is loosely connected to it (e.g. by a spring-like linkage. whose strain we can measure) as not to be acted upon by that force directly. If you move the casing of an accelerometer, the sprung mass inside it lags behind, and thereby the acceleration can be measured via strain gauges or whatever. Gravity defies accelerometers because, unsurprisingly, gravity acts on all of the the masses contained in an object equally. (At least any gravitational field you are likely to encounter in ordinary experience is going be almost perfectly uniform across an everyday object.) It is when you are in free-fall, that is when you're accelerating due to gravity. And that's exactly when the accelerometer doesn't tell you anything, because every part of the object is in the same free-fall; all of you is accelerating. The accelerometer is differential. It doesn't see a difference, so it doesn't see acceleration. You now that free-fall is acceleration because orbiting satellites are in free fall and they follow circular paths. Objects will not move in a circle unless a force accelerates them toward the center. Like when you spin a mass on the end of as string, it goes in a circle due to the centripetal force exerted by the tension carried in the string. When you're standing on the planet, your accelerometer is lying to you. Gravity is acting on the sprung mass inside the accelerometer, and it's also acting on the case which holds that mass. But the case is constrained from moving, whereas the sprung mass isn't. So a differential strain develops, which "looks and feels" like acceleration. In summary, an accelerometer is an instrument which measures the acceleration due to a force which is applied just to its casing, and not to some critical piece of mass held inside. Gravity causes equal acceleration of the casing and that piece of mass, and so gravitational acceleration is immeasurable by that accelerometer. Acceleration can be measured with regard to some frame of reference via distance and time calculations.