Transcript Newton’s Universal Law of Gravitation

Newton’s Universal
Law of Gravitation
Answer Me!!!

How does the force of gravity affect
objects with similar (very large) masses?
Force Due to Gravity


Gravitational Force (FG) is the attractive force between
two objects.
Gravitational Force can be determined by:
Gm1m2
F G
2
r


G is universal gravitational constant
(6.67x10-11 N*m2/kg2)
r is radius or distance between centers
Example: Earth-Moon
FG from Earth pulls on Moon
Earth
EQUAL AND OPPOSITE
FG from Moon pulls on Earth
Moon
Calculate the force of gravity between the Earth
and the Moon. (Hint: Use your reference Table)
List of Physical Constants
Name
Symbol
Universal Gravitational Constant
G
Value
6.67 x 10-11 N*m/kg2
Mass of Earth
5.98 x 1024 kg
Mass of Moon
7.35 x 1022 kg
Mean distance: Earth to Moon
3.84 x 108 m
Gm1m2
FG 
r2
2
6.67  1011 N m kg 2 5.98 1024 kg  7.35 1022 kg
FG 
(3.84 108 m) 2
F G  2.0  1020 N
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?
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?
Answer Me!!!

If there were no nearby objects to feel
Earth’s gravity, would there be a
gravitational force? Explain.
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.

Gravitational Field Strength

Remember:
FG
g
m object
and
FG 
Gm planetm object
r2

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?
Gravitational Force
Practice Problem 3
Mass
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?