What if you lived on Mars?

When you stand on a scale, it shows a number. That number tells how hard Earth pulls on you.

What would the scale say on Mars?

Step on a bathroom scale and it shows a number. Most people call that number their weight. But the scale is really measuring how hard the planet under you pulls you down.

Mars is a smaller planet than Earth. So what would that scale show if you took it to Mars? And how would it feel to walk and jump there? In this lab you can travel to Mars in a model and find out.

Everyday language mixes up mass and weight. Mass, measured in kilograms, is how much matter you contain. Weight, measured in newtons, is the force of a planet's gravity on that mass.

This lab asks what changes, and what does not, when a person moves from Earth to Mars: the scale reading, the force, the height of a jump and the time spent in the air.

On Earth, a child might weigh 30 kilograms on the scale.

When they jump, they go up a little and come down fast.

In the model, a child with a mass of 30 kilograms stands on a scale on Earth. The scale shows 30 kilograms, because bathroom scales are made to work on Earth.

Now the child jumps, leaving the ground at 2.4 meters per second. They rise about 29 centimeters, almost the length of a 30-centimeter school ruler, and are back on the ground in about half a second.

For m = 30 kg at g = 9.81 m/s², the model gives a weight of 294 N and, by calibration, a scale reading of 30 kg. A take-off speed of 2.4 m/s gives a jump height v²/2g of 0.29 m and an air time 2v/g of 0.49 s.

A bathroom scale measures force and divides by Earth's standard gravity to display 'kilograms', which is why it is only correct on Earth.

In our pretend lab, Olly takes the scale to Mars.

Now it shows only about 11 kilograms! You are not smaller. Mars just pulls less.

Choose Mars. The same child, still 30 kilograms of child, now makes the Earth scale show about 11 kilograms: a little more than a third of the Earth reading. Nothing about the child has changed; Mars simply pulls less.

Now jump with the same leg push. The child rises about 78 centimeters, more than two and a half times as high as on Earth, and stays in the air for about 1.3 seconds.

At g = 3.71 m/s² the model gives a weight of 111 N, a scale reading of 11.3 kg (37.8 percent of the Earth value), a jump height of 0.78 m and an air time of 1.29 s, both larger by 9.81/3.71 ≈ 2.6.

This is a model, not a visit: it assumes the same take-off speed on both worlds and ignores the spacesuit anyone on Mars would need.

Big planets pull hard. Smaller planets pull less.

Mars is smaller than Earth, so it pulls on you less.

Your mass is how much stuff you are made of, and it is the same everywhere. Your weight is how hard a planet pulls on that stuff. Mars has much less mass than Earth, so its pull at the surface is weaker: a little over a third as strong.

The scale reads less because the pull is less. And with a weaker pull slowing you down, the same jump carries you higher before you fall back.

Surface gravity depends on a planet's mass and radius, g = GM/R². Mars has about 11 percent of Earth's mass and 53 percent of its radius, which together give about 38 percent of Earth's surface gravity.

The model's limits: gravity is uniform during the jump, there is no air resistance, and the jumper's take-off speed is the same on every world. Real low-gravity jumps depend on footing and on how well a person can push off, so they would not scale exactly as 1/g.

Mars is cold and dusty. Its air is very thin.

A day on Mars is a little longer than a day on Earth.

Feeling lighter would only be the start. Mars is a cold, dusty desert world with very thin air, made mostly of carbon dioxide. A day on Mars, called a sol, lasts about 24 and a half hours, but a Martian year lasts 687 Earth days.

NASA says that standing on Mars's equator at noon would feel like spring at your feet and winter at your head. NASA says people would not be able to breathe the air on Mars, so anyone living there would need sealed homes and spacesuits.

Mars's atmosphere is about 95 percent carbon dioxide, with a mean surface pressure of about 6 millibars, under 1 percent of Earth's. Its average temperature is about −59 °C, and NASA notes that because the air is so thin, heat from the Sun escapes easily.

A sol lasts 24.66 hours and a year 687 days. NASA states plainly that people would not be able to breathe the air on Mars, so anyone living there would have to bring their own air and stay sealed inside homes and suits. All of that lies beyond this weight model.