When an object is taken from the Earth to the Moon, its mass:

Mass and weight are two different quantities, though they are often confused in everyday speech.

Mass is the amount of matter contained in an object. It is a scalar quantity, measured in kilograms (kg). The mass of an object is constant; it does not change from place to place, whether the object is on the Earth, the Moon, in space or anywhere else. Mass is measured using a beam balance (physical balance), which compares the object with standard masses. Mass is also a measure of an object's inertia, its resistance to a change in its state of rest or motion.

Weight is the force with which a planet or other body pulls an object towards itself due to gravity. It is a vector quantity, directed towards the centre of the planet, and is measured in newtons (N). Weight = mass × acceleration due to gravity (W = mg). Since the value of g changes from place to place, weight changes too. Weight is measured using a spring balance.

The acceleration due to gravity on the Moon is about 1.62 m/s², roughly one-sixth of that on the Earth (9.8 m/s²). This is because the Moon has much less mass (about 1/81 of the Earth's mass) and a smaller radius (about 1/4 of the Earth's radius). So an object weighs about one-sixth as much on the Moon as on the Earth. For example, an astronaut with a mass of 60 kg weighs about 588 N on Earth, but only about 98 N on the Moon. However, the astronaut's mass is still 60 kg.

This is why astronauts on the Moon, such as Neil Armstrong and Buzz Aldrin in 1969, could jump and move with long, bounding steps. In deep space, far from any planet, objects become nearly weightless, but they still have their full mass.

Why not the other options?

• ✗Becomes one-sixth: this is true of weight, not mass.
• ✗Becomes six times: neither mass nor weight increases on the Moon.
• ✗Becomes zero: mass never becomes zero; even weight is zero only in free fall or deep space.