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Ali Hamaiz

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In summary, g is a vector pointing to the center of the Earth that has a positive magnitude when used in the upwards direction and a negative magnitude when used in the downwards direction.

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Ali Hamaiz

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Svein

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g is a *vector *(pointing to the center of the Earth).

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CWatters

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Ali Hamaiz said:I threw a ball vertically upward the value of g at its max height (vi=0) ,what will be the value of g +10 or -10 m/s^2. I think it can be both if you consider the cartisean plane's cordinate , it depends upon refrence.

What sign did you use for the initial velocity? ditto the displacement/height?

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Ali Hamaiz

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This means with the sign of Vi you decide the value of g to be positive or negative.

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CWatters

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Correct. It depends which direction (up or down) you define as positive.

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jtbell

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If position, velocity, and acceleration are defined to be positive in the upwards direction and negative in the downwards direction, then the (y-component of) acceleration of a freely-falling object is ##a = -g## (more precisely ##a_y = -g##) and its position as a function of time is ##y = y_0 + v_{0y} t + \frac 1 2 a_y t^2 = y_0 + v_{0y} t - \frac 1 2 gt^2##.

If position, velocity, and acceleration are defined to be positive in the downwards direction and negative in the upwards direction, then the (y-component of) acceleration of a freely-falling object is ##a = +g## (more precisely ##a_y = +g##) and its position as a function of time is ##y = y_0 + v_{0y} t + \frac 1 2 a_y t^2 = y_0 + v_{0y} t + \frac 1 2 gt^2##.

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sophiecentaur

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Soon your diagram can be in your head.

- #8

Ali Hamaiz

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I got it thanks .

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David Lewis

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If you call the directional sense of gravitational force negative, then

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Best practice is to define your coordinate system on the paper with y clearly pointing up. But if you point y down, gravitational acceleration is going to be positive.

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A.T.

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Svein said:g is avector(pointing to the center of the Earth).

jtbell said:gis defined as apositivenumber, themagnitudeof the (vector)

It basically boils down to what you mean by "g".

Last edited:

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The whole exercise was meant to show that the location on where we define to be "zero" and the orientation of our coordinate axis are really arbitrary, and that no matter how we do this, it should not affect the final answers. Mother Nature doesn't give a hoot on which direction we call "positive" and "negative", and thus, your answer shouldn't either.

Zz.

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CWatters

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ZapperZ said:The whole exercise was meant to show that the location on where we define to be "zero" and the orientation of our coordinate axis are really arbitrary, and that no matter how we do this, it should not affect the final answers. Mother Nature doesn't give a hoot on which direction we call "positive" and "negative", and thus, your answer shouldn't either.

...as long as they are consistent in their definition.

No, the value of g can be either positive or negative depending on the location on Earth. At the equator, g is positive, while at the poles, it is negative. In most other locations, g is positive but can vary slightly.

The value of g is measured using a device called a gravimeter, which measures the gravitational acceleration of an object. This can also be calculated using the formula g = Gm/r^2, where G is the universal gravitational constant, m is the mass of the Earth, and r is the distance from the center of the Earth to the object.

The value of g can be affected by factors such as altitude, latitude, and local geology. It can also vary slightly due to the rotation of the Earth and the gravitational pull of other celestial bodies.

Yes, the value of g can change over time due to factors such as tectonic movements and changes in the Earth's mass distribution, but these changes are typically very small and difficult to measure.

Knowing the value of g is important for a variety of scientific and practical reasons. It helps us understand the structure and composition of the Earth, and it is also crucial for many engineering and navigation applications.

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