TheAlgorithms/Python · error · ValueError

Impossible gravity

Error message

Impossible gravity

What it means

Raised by archimedes_principle when gravity is negative. Unlike density and volume, gravity of exactly 0 is allowed (free-fall / orbit, returns 0.0) — only strictly negative values raise, since negative gravitational acceleration is unphysical in this model. It is the last of the three ordered checks.

Source

Thrown at physics/archimedes_principle_of_buoyant_force.py:54

    ValueError: Impossible object volume
    >>> archimedes_principle(fluid_density=0, volume=0.7)
    Traceback (most recent call last):
        ...
    ValueError: Impossible fluid density
    >>> archimedes_principle(fluid_density=997, volume=0.7, gravity=0)
    0.0
    >>> archimedes_principle(fluid_density=997, volume=0.7, gravity=-9.8)
    Traceback (most recent call last):
        ...
    ValueError: Impossible gravity
    """

    if fluid_density <= 0:
        raise ValueError("Impossible fluid density")
    if volume <= 0:
        raise ValueError("Impossible object volume")
    if gravity < 0:
        raise ValueError("Impossible gravity")

    return fluid_density * gravity * volume


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass the magnitude of gravitational acceleration (e.g. 9.8 or 9.81 m/s^2), not a signed vector component
2. Use gravity=0 deliberately for free-fall/orbital scenarios — it is supported
3. If your coordinate convention encodes gravity as -9.8, convert with abs()

Example fix

# before
archimedes_principle(fluid_density=997, volume=0.7, gravity=g_vec.y)  # -9.8 -> ValueError

# after
archimedes_principle(fluid_density=997, volume=0.7, gravity=abs(g_vec.y))

def valid_gravity(gravity) -> bool:
    return gravity >= 0  # 0 is allowed (free fall); only negative raises

When it happens

Trigger: Calling archimedes_principle(gravity=-9.8, ...), e.g. by sign-flipping an acceleration value or using a downward-positive coordinate convention.

Common situations: Physics engines or coordinate systems where the gravity vector is expressed as negative-y, and the signed component is passed instead of its magnitude.

Related errors

• Impossible fluid density
• Impossible object volume
• One and only one argument must be 0
• You cannot supply more or less than 2 values
• Expected a_coeffs to have {self.order + 1} elements for {sel

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/32620fd3e24624d4. Report an issue: GitHub.