Back To Course

AP Physics 1: Exam Prep12 chapters | 137 lessons

Watch short & fun videos
**
Start Your Free Trial Today
**

Start Your Free Trial To Continue Watching

As a member, you'll also get unlimited access to over 70,000 lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed.

Free 5-day trial
Your next lesson will play in
10 seconds

Lesson Transcript

Instructor:
*David Wood*

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this lesson, you will be able to explain what the gravitational constant is and explain how the Cavendish Experiment can be used to figure out the value of big-G. A short quiz will follow.

There are two gravitational constants that people tend to get mixed up. The first is the acceleration due to gravity (or gravitational field strength), which is represented by *g* and is an average of -9.8 m/s^2 on Earth. But then there's *G*. *G* is the gravitational constant of the universe. In our universe, it's 6.67 x 10^-11 N(m/kg)^2, and it's the same everywhere in the universe.

*G* is the constant you find in Newton's Universal Law of Gravitation. The **law of gravitation** says that every object in the universe attracts every other object. And it can be represented by this equation, *F*g = *G* x m1 x m2/d^2, where *F* is the force between two objects, M1 is the mass of one object, M2 is the mass of the other object and *d* is the distance between them. And this is where we use our value of *G*. F*g* = *G* x m1 x m2/d^2.

In 1797, Henry Cavendish conducted the first successful experiment to find the value of the gravitational constant. The idea for the experiment was constructed earlier in 1783 by John Michell, who created the torsion balance apparatus that Cavendish used. Michell, sadly, died before completing his work, and so, the baton passed to Cavendish.

The equipment looked something like this, though we can draw a simpler version to make it easier to understand. It is essentially a rotating balance. You have two small masses and two large masses, and you hang them like so:

The small masses move because of the gravitational attraction of the larger masses, causing the torsion wire to rotate. The apparatus was also encased in a box to avoid any impact from air motions. The experimental set-up was super sensitive and could detect even tiny deviations using Vernier scales.

The specific way Cavendish calculated the value of *G* was a bit more complicated than it sounds. It involved finding the wire's torsion coefficient, the torque exerted per degree of twist. By timing the rate of rotation of the balance rod (which had a period of oscillation of around 20 minutes), combined with the mass and length of the balance, the torsion coefficient could be calculated. Cavendish had to make all these measurements while the equipment was continually moving - the equipment was incredibly sensitive and always in motion.

Cavendish's ultimate goal was to calculate the density of the earth. That is ultimately what motivated the experiment, but the first step in doing that was to calculate the value of *G*. The experiment was a huge success, and the accuracy of the value wouldn't be improved upon again for a hundred years.

*G* is the constant you find in Newton's Universal Law of Gravitation. The **law of gravitation** says that every object in the universe attracts every other object, and it can be represented by this equation, *F*g = *G* x m1 x m2/d^2, where *F* is the force between two objects, M1 is the mass of one object, M2 is the mass of the other object, *d* is the distance between them and *G* is the gravitational constant.

In 1797, Henry Cavendish conducted the first successful experiment to find the value of the gravitational constant. The equipment looked like the set in the section above. You have two small masses and two large masses hanging in the air. The small masses move because of the gravitational attraction of the larger masses, causing the torsion wire to rotate. The experiment was a huge success, and the accuracy of the value wouldn't be improved upon again for a hundred years.

Upon completion of this lesson and its transcript, you could potentially:

- Provide definition for
*G* - State the law of gravitation
- Write the equation for the law of gravitation
- Outline the design, purpose and importance of Henry Cavendish's experiment

To unlock this lesson you must be a Study.com Member.

Create your account

Already a member? Log In

BackDid you know… We have over 95 college courses that prepare you to earn credit by exam that is accepted by over 2,000 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

You are viewing lesson
Lesson
7 in chapter 7 of the course:

Back To Course

AP Physics 1: Exam Prep12 chapters | 137 lessons

- Uniform Circular Motion: Definition & Mathematics 7:00
- Speed and Velocity: Concepts and Formulas 6:44
- What is Acceleration? - Definition and Formula 6:56
- Centripetal Force: Definition, Examples & Problems 5:57
- Newton's Law of Gravitation: Definition & Examples 6:35
- Gravitational Attraction of Extended Bodies 7:39
- Cavendish's Gravity Experiment & the Value of G 3:40
- Graphing the Motion of Objects: Physics Lab 3:17
- Gravitational vs. Inertial Mass: Physics Lab
- Go to AP Physics 1: Motion

- NCLEX Information Guide
- TEAS Information Guide
- HESI Information Guide
- Business 329: Retail Operations
- Computer Science 320: Digital Forensics
- Messaging in Business Communication
- Retail Market Selection
- Retail Merchandise Management
- The Study of Retail
- Retail Sales Operations
- How Long is the Praxis Test?
- Praxis Tests in North Carolina
- NES Test Registration Information
- Praxis Tests in Utah
- How Much Does The Praxis Cost?
- Praxis Test Accommodations
- Praxis Tests in Wyoming

- Trade Credit: Advantages & Disadvantages
- Social Construction of Race & Ethnicity
- Geography of Southwest Asia
- Comparisons of Equality in Spanish
- Effective Delegation: Scenarios & Application
- The Cultural Impact of Digital Communication
- Conflict Resolution Skills: List & Examples
- What is Mass Media Research? - Definition & Examples
- Quiz & Worksheet - Pharmacokinetics & Pharmacodynamics
- Quiz & Worksheet - What is Prim's Algorithm?
- Quiz & Worksheet - Binary Files in C
- Quiz & Worksheet - The Progressive Era & Child Labor
- Quiz & Worksheet - Reasons to Use a DBMS
- International Law & Global Issues Flashcards
- Foreign Policy, Defense Policy & Government Flashcards

- Supplemental Science: Study Aid
- Psychology 107: Life Span Developmental Psychology
- AP Chemistry Textbook
- High School Trigonometry: Help and Review
- AP World History: Help and Review
- Compass Writing Test: Modifiers & Clauses
- CEOE Business Education: Environmental Law
- Quiz & Worksheet - Trochaic Meter
- Quiz & Worksheet - Iambic Meter
- Quiz & Worksheet - Addition with One-Digit Integers
- Quiz & Worksheet - Writing Repeating Decimals as Fractions
- Quiz & Worksheet - Area Calculations with Counting Method

- Translating a Multiplication Statement into an Algebraic Expression
- How to Find the Volume of a Box
- AP Biology Exam Scoring Information
- Earth Day Project Ideas
- American Dream Lesson Plan
- Three Branches of Government Lesson Plan
- Thanksgiving Lesson Plan
- What's the Common Core Framework?
- How to Study for SAT Subject Tests
- French and Indian War Lesson Plan
- History of Halloween Lesson Plan
- What Are Good SAT Subject Test Scores?

Browse by subject