**Goal: **

The objective of this lesson is for students to be familiar with Sir Isaac Newton, the development of his Law of Universal Gravitation. Students should be able to complete quantitative calculations using the Law of Universal Gravitation, understand the proportional nature of the equation, and be able to distinguish between mass and weight. Lastly, student will observe trends in the change of their weight on different planets, due to changes in gravity.

**Overview: **

In pairs or small groups, students will be challenged to not only make a list of the basic forces they believe to exist in our physical world, but also then to rank the four actual fundamental forces is order of strength. Having then introduced Gravity as the weakest of the forces, groups will proceed to research gravity by visiting five different websites. Sites include information on Newton himself, the development of the Law of Universal Gravity, its mathematical applications, weight and mass, and more. For each site visited, groups will respond a series of questions which will be turned in. Class will then review the questions as a whole, and discuss gravity, Newton, and the Internet.

**Materials:**

Computers with Internet access

**INVITATION**

Students should be paired off or placed in small working groups. Each group will then be challenged to make a list of the "universal forces" scientists believe exist in our physical world. A list with suggestions from all groups should then be compiled on the board. The teacher should then point out and briefly describe only the four basic forces, eliminating and adding forces to the master list where necessary. Groups are then challenged to rank these four forces in order from strongest to weakest. Teacher should take some suggestions from the groups until the correct order is ascertained. This serves as an introduction to their next area of study: gravity, the weakest of the forces.

**EXPLORATION**

Each pair or group should begin by visiting the Official Isaac Newton Home Page. Groups should read this site and record some personal and historic data about the scientists responsible for our understanding of gravity. Each group should then have created a brief biographical summary of Newton.

Groups are then to proceed to the following website on Newton and Gravity. After reading this site, each group should respond the following questions. This site will give students insight into the theory and concept of gravity, as well as introduce its quantitative nature.

Website #1:http://csep10.phys.utk.edu/astr161/lect/history/newtongrav.html

**Questions:**

- Describe Newton's possible train of thought as he developed the theory on gravity?
- What is the Law of Universal Gravitation in written and mathematical terms?
- What does each variable of the equation represent?
- What is the relation between gravity and orbit?

Having completed these questions, groups should visit the next website on gravity. This site will provide students with the relationship between gravity and orbits, as well as complement the previous information on the Law of Universal Gravitation. Students will also learn about the proportional nature of the equation.

Website #2: http://www.teacherlink.usu.edu/nasa/microgravity/gravity.html

**Questions:**

- This site discusses the relation between Newton's Laws of Motion, and his development of the Law of Universal Gravitation. Describe briefly this relationship.
- What does it mean to say that the Force of gravity is proportional to the masses of the bodies, and inversely proportional to the distance between them?
- What is the term and value of "G" (include units)?
- Each group should then proceed to the following interactive website, where students will differentiate between mass and weight, and observe the value of their weight on the different planets.

Website #3: http://www.exploratorium.edu/ronh/weight/index.html

**Questions:**

- Input your weight on earth, and compare your weight on the nine planets. What trends do you observe?
- What is the difference between "weight" and "mass" ?
- Having completed this step, students should proceed to the last website where they will calculate and compare the force of gravity between several bodies of the solar system.

Website #4: http://www.nasm.edu:2020/CEPSDOCS/SNAPSHOT/DATA.html

**Questions:**

- Utilizing the Law of Universal Gravitation and the data contained in this site, calculate the force of gravity between any one planet and four other planets (for example: Mars-Earth, Mars-Jupiter, Mars-Pluto, etc.)
- Do you observe any trends in the gravitational forces?

**EXPLANATION**

The class should meet as a whole once each group has completed the project or the allowed time has expired. Teacher should cover all the questions involved the project one by one. Responses to the questions should be provided by varying students from diverse groups. Dialogue between teacher and students should be encouraged to include opinions about the different sites, utility of the Internet, and applications of gravity(orbit, etc.). Each student should turn in a set of responses to the questions.

**TAKE ACTION**

Expansion studies and research from gravity are abundant. Options include space travel, space missions, escape velocity, NASA, orbital motion, the solar system, any of the fundamental forces, unified force theory, etc. Should you desire to conduct an in-depth study of Orbital Motion and its relation to Binary Stars, be sure to check out the following site, as well as The Nine Planet-Tour of the Solar System

http://zebu.uoregon.edu/~soper/Stars/orbits.html

**Nine Planet-Tour of the Solar
System**

http://seds.lpl.arizona.edu/nineplanets/nineplanets/nineplanets.html