Gravity and Weight on Other Planets

Objectives

• Students will practice multiplication skills.
• Students will learn about mass, weight, and gravity.

Materials

• Scale (one per class is plenty)
• Calculator (optional)
• Weight Chart (see lesson)

Procedure

1. Start with a mini lesson about mass, weight, and gravity. Here is some background information:

   Weight is a measurement of the force on a object caused by gravity trying to pull the object down. Mars has less gravity than Earth. Therefore if you were on Mars you'd weigh less because the force of gravity wouldn't be as strong as it is here on Earth.

   Does this mean you would suddenly be thinner on Mars? No. You would have the same amount of mass as you do on Earth. (Mass is the amount of stuff inside an object.)

   So, on Mars, your mass would be the same as it is here on Earth. But you'd weigh less because Mars has less gravity than Earth.

   Gravity is an attractive force. This doesn't mean it's pretty. What "attractive" means is that an object's gravity pulls other objects toward it. Look at the chart (see below). The Earth's gravity naturally pulls us, and everything else, toward the center of the planet, which keeps us from drifting off into space.

   The Earth isn't the only thing that has gravity. In fact, every single object in the universe has gravity. The tables you're sitting at have gravity. They are pulling you towards them. You have gravity, and you are pulling the tables towards you. We can't see or feel these things happening because people and tables have a such a small mass that the effects of gravity cannot be seen.

   Mass is the amount of stuff contained inside an object. It takes a lot of mass to make a lot of gravity. The Earth has a lot of mass, so it has a lot of gravity. The moon's gravity is about 1/6 the amount of the Earth's because the moon has less mass than the Earth.

   So what does all this have to do with weight? Well, weight is the force on a object caused by gravity trying to pull the object down. A scale measures how much gravity your mass has. A person with more mass has more gravity, and therefore weighs more.

   You've probably seen video footage of astronauts walking on the moon. They seem to float between each step. Remember that the moon has about 1/6 the amount of gravity that the Earth has? Well, if you went to the moon, you'd weigh less than you do here on Earth. Does this mean you would suddenly be thinner on the moon? Absolutely not. Your mass would be the same -- there is no less of you on the moon. But your weight is different because the moon's gravity is different.

   Instructions for the Project:

2. Look at the Weight Chart.

3. Weigh yourself, or guess what you weigh.

4. Record your mass in the chart below. Your mass is your weight on Earth.

5. Multiply your mass times the gravity in each row to figure out your weight at each location.

6. Where do you weigh the most? Where do you weigh the least?

Weight Chart

To calculate your weight: mass x gravity = weight

*On Aug. 24, 2006, Pluto got "demoted" to dwarf planet status. Read more about Pluto's new status at our sister site, Fact Monster.