Download Gravity – and the Rules of Attraction

Gravity – and the Rules
of Attraction
Newton vs. Einstein
Mass Vs. Weight
Mass is the amount of
matter that makes up an
object.
Mass of an object does
not change (ex. A bar of
gold will always have the
same mass.)
Weight is the
measurement of the
force of gravity on an
object (gravitational pull
on the mass).
Measured in Newtons
Ex. 1- scales measure the
force that Earth exerts
on the object.
Ex. 2 – the weight of a
bar of gold will change
on different planets.
How is mass different from weight?
mass – the amount of matter in an object
 weight – the force that acts upon an object

You are weightless
in free-fall!
Gravity – the force of attraction between any 2
masses, any 2 bodies, or any 2 particles.
Gravity exists between all objects
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Gravitational pull is dependent on MassSmall mass = small gravitational pull
Large mass = big gravitational pull
Small gravitational pull = small weight
Large gravitational pull = large weight
Ex. The Moon is 1/6th the size of the Earth. So an object
on the Moon would weigh 1/6th as much.
Thought Question
On the Moon:
A.
B.
C.
D.
My weight is the same, my mass is less.
My weight is less, my mass is the same.
My weight is more, my mass is the same.
My weight is more, my mass is less.
On the Moon…
A.
B.
C.
D.
My weight is the same, my mass is less.
My weight is less, my mass is the same.
My weight is more, my mass is the same.
My weight is more, my mass is less.
Gravity on Earth
Acceleration due to gravity on Earth is 9.8 meters/
second squared.
Free falling objects increase in speed 9.8 meters
per second for every second they fall.
Rate of acceleration is independent of mass.
Ex. A golf ball and a shot put dropped at the same
time from the same height will reach Earth at the
same time.
For this to be true- what must we leave out?
The Acceleration of Gravity

All falling objects
accelerate at the same
rate (not counting
friction of air
resistance).
 On Earth, g ≈ 9.8 m/s2:
speed increases 9.8 m/s
with each second of
falling.
One Exception for Gravity on
Earth……
Earth has an atmosphere- so, Gravity is:
NOT independent of air resistance
Air Resistance slows down acceleration
In vacuum, all objects fall at the same
rate.
Without a vacuum- objects fall at rates
depending on their surface areas.
Acceleration of Gravity of an
object on Earth is independent
of…
1. The mass of the object
2. Velocity of the object parallel to the ground
(I.e. horizontal velocity)
3. Then this means…
If an object …
Is traveling at a certain velocity parallel to the
Earth’s surface,
It will fall to the Earth at the same rate as a
stationary object (falling straight to Earth) dropped
at the same height.
Ex. Simultaneously shoot a bullet from a gun and
drop a bullet straight from the same height- both
bullets will hit at the same time.
The Effect of Gravity on Earth
Keeps our Earth’s atmosphere, oceans, and
inhabitants from drifting into space
 Pulls rain into rivers and eventually into the
oceans
 Effects the way our muscles and bones
develop and function. (I.e. bench pressing,
dunking a basketball.)

How did Newton change our view of the Universe?

Sir Isaac Newton
(1642-1727)
Realized the same physical laws
that operate on Earth also operate in
the heavens
 one universe
 Discovered laws of motion and
gravity
 Much more: experiments with light;
first reflecting telescope,
electromagnetic spectrum,
calculus…
 Is most famous for his work“Principia” which was two years of
thought and scribbling, but was
only a recounting of what he could
remember.
Newton was a neat guy….
Described as “odd, brilliant beyond measure, solitary,
joyless, prickly to the point of paranoia, famously
distracted.”
 Capable of riveting strangeness
 Once inserted a “bodkin” – a long needle used for
sewing leather- into his eye socket and rubbed it
around “betwixt my eye and the bone as near to the
backside of my eye as I could” just to see what would
happen.
 A hair sample analyzed in the 1970s found a high level
of mercury – 40 times the natural level found for most
people.

Newton: Ideas About Gravity
Gravity is apparent
everywhere on Earth
from the mountains to
the valleys
 He wondered – Does
gravity…
 Extend to the Moon?
 Account for Earth and
Moon movement?
 Motions of other
planets?

Universal Law of Gravitation
• Every mass attracts other mass through the
force of gravity. Anything with a mass has
its own gravity, although it may be very
small
This means that:
As objects get farther
apart, the effect of
gravity drops
dramatically.
Ex. An object 1 km
from Earth is pulled
much more strongly
than an object 3km
away.
Questions to consider!
1. Why do tides occur in the lakes and oceans on
Earth?
2. How do planets in our solar system stay in orbit?
3. How does the Sun’s force travel through so much
empty space?
4. What would happen if a person stepped out into
space and opened a package of Skittles?
M&Ms?
Einstein and Relativity That
Anyone Can Understand
First things first – to understand where Al was
coming from, we must remember the following:
 The speed of light is the universal speed limit
(299,792.458 km/ sec.)
 The flow of time is dependent upon the state of the
clock
 Space and time are interconnected. (adding a
fourth dimension)
 The speed of light in empty space can not be
reached or exceeded by any massive object in the
universe.
Einstein’s New Theory of
Gravity
Gravity is the result of the interaction between
matter and space – between the Earth and the
space immediately surrounding the Earth.
Spacetime and Einstein's
Gravity
The mass of an object
creates a “warp” or
“dip” in spacetime.
The greater the mass,
the larger the warp in
spacetime.
The size of the warp
determines the motion
of the objects around
it.
Gravity is Curved Space
For planets orbiting
the Sun – they are
effected by the largest
warp in spacetime.
The Sun is the most
massive, so it has the
most gravity.
This ‘gravity’ tells that
planets how to move.
If Spacetime was a
Trampoline
Picture Spacetime as a trampoline holding 100
people of equal weight.
If everyone has their own space, the
trampoline should remain evenly
distributed. (with no large lumps.)
What would happen if everyone walked into
the middle, creating a large warp in
spacetime?
As the people move towards the
center- the “warp” grows larger.
Eventually, even the furthest person
is effected by the warped spacetime
Gravity, Escape Velocity, and
Black Holes
Now that we understand a little more about
gravity: ponder these questionsHow fast would an object have to go to escape
the gravity of Earth?
Is it possible to have an object so massive that
the escape velocity is beyond the speed of
light?
What about a “Theory of Everything?”