**How to determine your weight in newtons on different planets****, just use a bathroom scale, calculator, pencil and paper. ****Weigh yourself, record it, then multiply by 4,5.**

**science.akisografi.com** – Throughout history many attempts have been made to explain gravity. In the fourth century B.C., Aristotle claimed that the Earth was made of four elements—earth, air, fire, and water— which had their natural places and toward which they tended to travel. He taught that heavier objects containing greater amounts of earth than others would fall toward Earth faster.

Galileo had a different view, which was that gravity causes all things to fall at the same acceleration. Acceleration is a change or increase in speed, and Galileo correctly believed that every falling object’s speed changed at the same rate. Legend has it that Galileo demonstrated his ideas about gravity to his students by dropping a cannonball and a smaller musket ball from the Leaning Tower of Pisa, and the balls hit the ground at the same time.

Sir Isaac Newton used the information from Galileo’s work to describe the force of gravity and the motion of objects throughout the universe. According to another legend, an apple fell on Newton’s head when he was sitting under an apple tree, and this started him thinking about falling things. The apple fell because of a force called gravity. Weight is the measure of gravity and one unit of weight is the newton (N), named in honor of Sir Isaac Newton.

Falling apples, people, or any other objects in free fall seem to be weightless. A free fall is the fall of an object in which gravity is the only force pulling it down. Since weight is a measure of the gravitational force on an object, objects in Earth’s gravitational field are never weightless. But since a scale under the feet of a falling person, such as a person jumping on a trampoline, would also be falling at the same rate, the person’s feet would not be pushing against the scale, and the person would have an apparent zero weight shown on the scale.

The German-born American physicist Albert Einstein (1879–1955) realized that free fall is an important clue to gravity. Einstein’s thoughts were the foundation of the ReducedGravity Program operated by the NASA Lyndon B. Johnson Space Center in Houston, Texas. This program was started in 1959 to test the effects of microgravity environments on humans, equipment, and experimental investigations, such as the motion of objects. (A microgravity environment is one in which an object’s apparent weight is small compared to its actual weight due to gravity.)

Today, experiments in microgravity environments can be performed aboard special airplanes that fly at specific speeds and paths to produce apparent weightless periods of about 25 seconds. The mass and size of a planet affect the strength of its gravity (g). Surface gravity is gravity at or near the surface of a celestial body. The gravity rate (G.R.) of a celestial body is its surface gravity divided by Earth’s. Earth’s G.R. is arbitrarily given a value of 1 g. The planets with a gravity rate less than 1 g are Mercury, Venus, Mars, Uranus, and Pluto. The remaining planets—Jupiter, Saturn, and Neptune—have a gravity rate of more than 1 g. On July 20, 1969, astronauts Neil Armstrong (b.1930) and Edwin Eugene (“Buzz”) Aldrin (b.1930) stood on Earth’s Moon. They were seen via satellite communication to leap around as if on trampolines due to the Moon’s gravity of 1⁄6 g.

**Purpose**

To determine your weight in newtons on different planets.

**Materials**

bathroom scale

calculator

pencil and paper

**Procedure**

1. Determine your weight in pounds by weighing yourself on the scale.

2. Calculate your weight in newtons (N) by using the calculator to multiply your weight in pounds by 4.5. For example, if you weigh 90 pounds, your weight in newtons would be:

90 pounds × 4.5 = 405 N

Record your weight on Earth in newtons in a weight data table like the one shown.

3. Determine and record in your Weight Data table what your weight would be on the different planets. Do this by using the calculator to multiply each planet’s gravity rate listed in the table by your weight on Earth. For example, if you weigh 405 N on Earth, your weight on Mercury, which has a gravity rate of 0.38, would be:

0.38 × 405 N = 153.9 N

**Results**

Your weight will vary on each planet. You would weigh the least on Pluto and the most on Jupiter.

**Why?**

Your weight is a measure of the force of gravity, which on Earth is the force with which Earth’s surface gravity pulls on an object. Earth’s gravity rate equals 1. Celestial bodies with a gravity rate greater than 1 have a surface gravity greater than that of Earth. Those with a gravity rate less than 1 have a surface gravity less than that of Earth. As shown in this investigation, your weight on each planet is calculated as the product of your weight on Earth times the gravity rate of each planet. The newton (N) is the SI unit of weight; the pound is the English unit of weight. Weight on celestial bodies in this investigation is measured in newtons.

**Try New Approaches**

Your apparent weight increases when you ride up in an accelerating elevator and decreases when you ride down. Investigate this for yourself by placing a bathroom scale on the floor of an elevator car. Stand on the scale and observe your weight when the elevator car is stationary. This will be your normal weight, which is equal to the force of gravity on your body. As the elevator car accelerates on the way up, the mass of your body doesn’t change but your apparent weight on the scale does.

This is because while you are being pulled down against the scale by gravity, the elevator car is pushing back with more force because it is accelerating upward. As the elevator car accelerates on the way down, you are being pulled against the scale by gravity, but the scale is moving away from you so your apparent weight decreases. In free fall, you and the scale would be moving at the same rate and your apparent weight would be zero.

**References**

Couper, Heather, and Nigel Henbest. How the Universe Works. Pleasantville, N.Y.: Reader’s Digest Association, 1994. Interesting facts and activities about gravity and other astronomy topics.

Filkin, David. Stephen Hawking’s Universe. New York: Basic Books, 1997. A brief history of the cosmos and other astronomy topics, including gravity.

Gilbert, Harry, and Diana Gilbert Smith. Gravity, the Glue of the Universe. Englewood, Colo.: Teacher Ideas Press, 1997. History of and activities about gravity.

VanCleave, Janice. Janice VanCleave’s Gravity. New York: Wiley, 1993. Experiments about weightlessness and other gravity topics. Each chapter contains ideas that can be turned into award-winning science fair projects.