Ideal Gas Molecular Motion Between Collisions

Steps:

• Low-pressure hydrogen approximates ideal gas behavior, where intermolecular forces are negligible except during collisions.
• Between collisions, no net forces act on a molecule.
• By Newton's first law, the molecule maintains constant velocity.
• Constant velocity means unchanging speed and straight-line path.

Why D is correct:

• Newton's first law states that without net force, an object moves with constant velocity, implying constant speed in a straight line.

Why the others are wrong:

• A: Changing speed and direction require forces, absent between collisions.
• B: Changing speed implies acceleration from forces, not present.
• C: Changing direction requires force to alter path, but none acts.

Final answer: D