TheAlgorithms/Python · error · ValueError

The mass of a body cannot be negative

Error message

The mass of a body cannot be negative

What it means

Raised by potential_energy(mass, height) in physics/potential_energy.py when mass < 0. Gravitational potential energy U = m*g*h requires a non-negative mass; mass 0 is allowed and returns 0.0. The mass check runs first, so a negative mass raises even if height is also invalid.

Source

Thrown at physics/potential_energy.py:51

    """
    >>> potential_energy(10,10)
    980.665
    >>> potential_energy(0,5)
    0.0
    >>> potential_energy(8,0)
    0.0
    >>> potential_energy(10,5)
    490.3325
    >>> potential_energy(0,0)
    0.0
    >>> potential_energy(2,8)
    156.9064
    >>> potential_energy(20,100)
    19613.3
    """
    if mass < 0:
        # handling of negative values of mass
        raise ValueError("The mass of a body cannot be negative")
    if height < 0:
        # handling of negative values of height
        raise ValueError("The height above the ground cannot be negative")
    return mass * g * height


if __name__ == "__main__":
    from doctest import testmod

    testmod(name="potential_energy")

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass a non-negative mass in kg: potential_energy(10, 5) -> 490.3325
2. Replace sentinel masses (e.g. -1) with a validation step that rejects the record before calling
3. If computing deltas, compute potential_energy on absolute masses and subtract the results instead of passing a negative delta mass

Example fix

# before
potential_energy(-10, 5)
# ValueError: The mass of a body cannot be negative

# after
potential_energy(10, 5)

if mass < 0:
    raise ValueError(f"mass must be >= 0, got {mass}")
potential_energy(mass, height)

try:
    potential_energy(mass, height)
except ValueError as e:
    if "mass" in str(e):
        raise ValueError(f"bad mass in payload: {mass}") from e
    raise

When it happens

Trigger: potential_energy(-10, 5); any call with a negative first argument, e.g. mass loaded from a physics body whose serialization used -1 for unknown mass.

Common situations: Using sentinel values like -1 for missing mass; importing bodies from game engines where negative mass means 'static/infinite'; sign errors from mass deltas (rocket propellant consumed) fed as absolute mass.

Related errors

• Mass can not be negative
• Gravitational force can not be negative
• Distance can not be negative
• The length should be non-negative
• The height above the ground cannot be negative

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/86915b037449b574. Report an issue: GitHub.