The Idea of Gravitation Ideas, Examples and Theories of Gravitation and how to use it

HW TALK

HW QUIZ

QUESTIONS TO START OFF 1) What creates gravity? 2) Does it have a speed? 3) Does it have a maximum range to be felt? 4) Can gravity repel objects instead of attracting?

In The Beginning A planet and star is formed when gas clouds get pulled together by gravity and become solid (or dense). Momentum of the clouds did not change, so the formed planet/star keeps rotating

There MUST be an idea that governs pulling atoms together, planets together, planets around stars, and keeps them moving in orbits. GRAVITY. The attractive force between any two objects. Whatever Joch, I already know about gravity! That was September, before I grew bitter at the world.

Gravity is the attraction between all masses. It is caused by the warping of space-time by mass itself. Of the 4 basic forces, it is the WEAKEST

Idea 1: Gravitational Field An object with mass creates a FIELD around it. This FIELD represents where another object in that region can feel a FORCE from that FIELD.

When two OBJECTS are near each other, they experience each others FIELDS, and experience an equal FORCE towards each other. Are the FORCES experienced by each the same? Yes…Newtons 3rd Law applies

The more MASS an object has, the stronger the field The more MASS an object has, the stronger the field. The more distance between the objects, the weaker the field. The mass MAKING the field we call the object. The mass that feels the field is called the test.

Example: You are on the earth Example: You are on the earth. You are the test for the Earth’s field at your center of mass And the Earth is the test for your field at the Earths center of mass The forces are equal.

Are the FIELDS of each object equal? No! Earth has more mass, so a stronger field. But your small mass barely interacts with it. The Earth’s huge mass really interacts with your weak field The forces from each are equal!

To calculate the field strength due to gravitation (an ACCELERATION) g = G(M/d2), where: g is the field strength/surface G is the gravitational constant 6.67x10-11 M is the object mass d is the distance between the center of masses of the two objects

Example

Example

A steel sphere of mass M and radius r is now replaced by a steel sphere that is three times the radius of the original. Now what is the surface gravitational field?

REMINDER SO FAR

REMINDER SO FAR

Important things to remember There is a difference between the FIELD strength overall vs. the FIELD strength compared to Earth Ex: A field strength of 25 is 2.5x Earth’s value.