Cavendish's Gravity Experiment & the Value of G

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Gravitational Field: Definition & Formula

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:02 What Is the…
  • 1:01 Cavendish Experiment
  • 2:47 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed

Recommended Lessons and Courses for You

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.

What Is the Gravitational Constant?

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, Fg = 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. Fg = G x m1 x m2/d^2.

Cavendish Experiment

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.

Cavendish experiment
equipment used in Cavendish experiment

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:

Diagram of Cavendish experiment
diagram of Cavendish experiment

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.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 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

Transferring credit to the school of your choice

Not sure what college you want to attend yet? 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.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account