1. Newton’s Universal Law of Gravitation

2. Answer Me!!! How does the force of gravity affect objects with similar (very large) masses?

3. Force Due to Gravity Gravitational Force (F G ) is the attractive force between two objects. Gravitational Force can be determined by: G is universal gravitational constant (6.67x10 -11 N*m 2 /kg 2 ) r is radius or distance between centers

4. Example: Earth-Moon Earth Moon F G from Earth pulls on Moon F G from Moon pulls on Earth EQUAL AND OPPOSITE Calculate the force of gravity between the Earth and the Moon. (Hint: Use your reference Table)

5. List of Physical Constants NameSymbolValue Universal Gravitational ConstantG6.67 x 10 -11 N*m/kg 2 Mass of Earth5.98 x 10 24 kg Mass of Moon7.35 x 10 22 kg Mean distance: Earth to Moon3.84 x 10 8 m

6. Practice Problem 1 When a satellite is a distance R from the center of Earth, the force due to gravity on the satellite is F. What is the force due to gravity on the satellite when its distance from the center of Earth is 3R?

7. Final Thought… An object weighs 100N on the Earth’s surface. When it is moved to a point one Earth’s radius above the Earth’s surface, what will it weigh?

8. Answer Me!!! If there were no nearby objects to feel Earth’s gravity, would there be a gravitational force? Explain.

9. Gravitational Field Strength A gravitational field is a region where gravitational force has the potential to exist. Gravitational Field Strength is a measure of how strong the force due to gravity is at that location. You know it as the acceleration due to gravity.

10. Gravitational Field Strength Remember:

11. Practice Problem 3 The following graph represents the relationship between gravitational force and mass for objects near the surface of Earth. What does the slope of the graph represent?

12. Practice Problem 4 A 70kg astronaut has a weight of 560N on the surface of planet Alpha. What is the acceleration due to gravity on planet Alpha?