What two factors affect the force of Gravity?
Gravity
It’s Universal – it’s everywhere!
The Standard Theory
Force
Gravity
Boson
Function
Range
(composite particle)
Graviton
Gravity curves space. And it
Indefinite
always attracts, never repels.
(property of
Gravity is the only force to
matter)
which all particles are subjected.
Electromagnetism Photon
The strong force binds quarks
into nucleons and nucleons into
nuclei.
Electromagnetism binds
electrons to the nucleus. By
doing so electromagnetism
allows all physical and chemical
processes to happen.
Weak Nuclear
Force
The weak force causes unstable Limited to the
particles and nuclei to decay.
atomic nucleus
(Nuclear Force)
Strong Nuclear
Force
Gluon (8 kinds)
Weak bosons
(3 kinds)
Limited to the
atomic nucleus
(Nuclear Force)
Indefinite
(property of
matter)
Newton’s Law of Universal Gravitation
G is a very small number (0.0000000000667)
Gravity is a weak force, this means that the force of
gravity is not noticeable unless there is a very large
mass involved (such as a planet or star).
That’s why we are not
revolving around one
another!
But the Earth and Moon
are large enough!
Gravity is universal –
it’s everywhere!
Gravity depends on mass
(amount of atoms)
Less mass means less
gravitational force
More mass means more
gravitational force
Newton’s Law of Universal Gravitation
Gravity pulls objects in a straight line towards each other.
Earth and Moon
Gravity depends on the distance
between objects
More distance means
less gravitational force
Less distance means
more gravitational force
Think of gravity like a
magnet. When magnets
are closer, the attraction is
stronger. When magnets
are further apart, the
attraction is less.
What two factors affect the force of Gravity?
Gravity
It’s Universal – it’s everywhere!
MASS
DISTANCE
Gravity
 Gravitational Force
 Affected by mass and distance
 The amount of Newtons that gravity pulls on an object
F = ma
 How fast an object falls due to gravity Force of gravity will
accelerate a mass.
 Called little g
 Gravitational Acceleration
 On earth little g = 9.8m/s/s
 So an object speeds up by about 10m/s every second when falling
 On the moon little g = 1.6m/s/s
 So an object speeds up by about 2m/s every second when falling
Gravitational Acceleration
Gravity depends on combined mass and the distance between the
two objects.
The acceleration of gravity decreases slowly with increased
distance/altitude:
On the surface of
earth the force of
gravity accelerates
objects down at
9.8m/s/s, but at
200 miles above
the surface little g
~ 9.5m/s/s
Gravitational Acceleration
Once the altitude becomes comparable to the radius of the
Earth (a distance thousands of miles away from earth), then
the gravitational acceleration becomes much smaller.
Once you are about 20,000 miles
above the surface, there is little gravity
– this is known as microgravity.
Gravitational Acceleration
 All objects on the surface of the earth accelerate downward at
9.8 m/s2 regardless of mass. Why? (Think about inertia…)
Remember F=ma As the force and mass change the acceleration stays the same.
More mass
•More g force
BUT
•More Inertia
SO
Same acceleration
100 kg
10 kg
Gravitational acceleration
g = 9.8 m/s2
Larger mass has more gravitational force,
greater pull, but it has more mass, more
inertia - so it is harder to accelerate;
Bigger F = Bigger M x same A
Less mass
•Less g force
BUT
•Less Inertia
SO
•Same acceleration
Gravitational acceleration
g = 9.8 m/s2
Smaller mass has less gravitational
force, lesser pull, but has less mass, less
inertia - so it is easier to accelerate;
Smaller F = Smaller M x same A
Gravitational Acceleration
 All objects on the surface of the earth accelerate downward at
9.8 m/s2 regardless of mass. Why? (Think about inertia…)
100 kg
10 kg
Gravitational acceleration
g = 9.8 m/s2
Gravitational acceleration
g = 9.8 m/s2
More mass means more gravity, but it also means more
inertia. The extra gravity gets cancelled out by the extra
inertia, so all object fall at the same speed regardless of mass.
Gravitational Acceleration
 So all object fall at 9.8m/s/s on the surface of the earth.
Gravity mini-experiment:
1. Crumble up (compress) a piece of paper.
2. Drop the paper from the height of your desk to the floor.
3. Leave a piece of paper flat.
4. Drop the paper from the height of your desk to the floor.
5. Observe how each object falls.
Discussion:
 Both object “want” to fall at 9.8m/s/s. Did each object fall
at the same rate downward? What did each object have to
push through? What would happen if the paper had nothing
to push through? Hammer vs Feather – Physics on the Moon
Weight
Gravity’s Effect on Mass
Weight = Mass x Acceleration of Gravity
W(Newtons) = m (kg) g(Meters/Sec )
2
9.8 (Newtons) =1 (kg) 9.8(Meters/Sec )
2
Weight is a Force measured in Newtons
As you travel further from the surface of earth, increasing distance,
then the gravitational force and gravitational acceleration decrease. If
you travel far enough then you have apparent weightlessness.
Word Magnet: What is Gravity?
Considered to
be a weak force
Attractive force
Gravitational Force
depends on the
total mass of the
two objects
Property of
Matter
Gravity
Gravitational Force
depends on the
distance between the
two objects
One of the four
forces of nature
Chapter 3.1 – Gravity
Topic: What affects the force of gravity?
Vocabulary (Define in your notebook):
Gravity
Weight
Orbit
Procedure: Complete using Window Notes
 Define the vocabulary words in your notebook. Paragraph
read section 3.1 (pages 76-83) with your lab group.
 Answer questions 1-6 on page 83 in your science notebook
 Extension Activity - Gravity and Orbits Interactive