# Gravity

Written by Jerry Ratzlaff on . Posted in Relativity

## Gravity

Gravity ( $$g$$ ) or gravitation is a force pulling togeather all matter.  Everything that has mass has a gavitational pull that is exerted on one another.  The larger the mass, the stronger the gravitational pull is exerted, this includes all matter.

## API Gravity

The oil industry uses the API Gravity or Gravity scale. If a fluids API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks. API gravity is thus a measure of the relative density of a petroleum liquid and the density of water, but it is used to compare the relative densities of petroleum liquids.

The relationship between API Gravity and specific gravity is as follows:

$$\large{ API_{gravity} = \frac{141.5}{SG} - 131.5 }$$

So using the above equation, an oil with a specific gravity of 1.0 would have an API Gravity of (141.5 1.0) -131.5 = 10.0 degrees API.

## Gravitational Acceleration

Gravitational acceleration ( $$g$$ ) (also known as acceleration of gravity) is the force on an object caused only by gravity.

### Gravitational Acceleration formula

$$\large{ g = \frac {G m} {r^2} }$$

Where:

$$\large{ g }$$ = gravitational acceleration

$$\large{ G }$$ = universal gravitational constant

$$\large{ m }$$ = planet mass

$$\large{ r }$$ = radius from the planet center

Solve for:

$$\large{ m = \frac {g r^2} {G} }$$

$$\large{ r = \sqrt { \frac {G m} {g} } }$$

## Newton's Law of Universal Gravitation

All objects in the universe exert a gravitational force of attraction on each other.

### Newton's Law of Universal Gravitation formula

$$\large{ F_g = G \frac {m_1 m_2} {d^2} }$$

Where:

$$\large{ F_g }$$ = gravitational force

$$\large{ d }$$ = distance between objects

$$\large{ G }$$ = universal gravitational constant

$$\large{ m_1 }$$ = mass of object 1

$$\large{ m_2 }$$ = mass of object 2

Solve for:

$$\large{ m_1 = \frac {F_g d^2} {G m_2} }$$

$$\large{ m_2 = \frac {F_g d^2} {G m_1} }$$

$$\large{ d = \sqrt { \frac {G m_1 m_2} {F_g} } }$$

## Specific Gravity

Specific gravity ( $$SG$$ ) (dimensionless number) is the density or ratio of any substance to another substance.  It sometimes may be called just gravity or relative density.  When calculating the specific gravity of a liquid or solid, water is normally the comparison (water has a specific gravity of 1).

Even though two objects are the same size, their density may be different. This is expressed in how much more weight the object is in comparison to the same amount of water.  Likewise a gas is compared to air.

### Specific Gravity formula

$$\large{ SG = \frac { \rho_s } { \rho_w } }$$

Where:

$$\large{ SG }$$ = specific gravity

$$\large{ \rho_s }$$  (Greek symbol rho) = sample density

$$\large{ \rho_w }$$  (Greek symbol rho) = water density

Solve for:

$$\large{ \rho_s = SG \rho_w }$$

$$\large{ \rho_w = \frac { \rho_s } { SG } }$$

## Specific Gravity conversion table

• This is a Density Conversion
Specific Gravity Conversion Table
MultiplyByTo Get
436995.7259 grain per cubic foot
252.8910451 grain per cubic inch
1 gram per cubic centimeter
1e+15 gram per cubic kilometer
1000000 gram per cubic meter
0.001 gram per cubic millimeter
1000000 gram per kiloliter
1000 gram per liter
1 gram per milliliter
0.001 kilogram per cubic centimeter
1e+12 kilogram per cubic kilometer
1000 kilogram per cubic meter
1e-15 kilogram per cubic micrometer
0.000001 kilogram per cubic millimeter
998.8473734 ounce per cubic foot
0.578036674 ounce per cubic inch
62.42796084 pound per cubic foot
0.036127292 pound per cubic inch
1 standard conditions
1 specific gravity, water

## Specific Gravity of materials Table

MaterialSpecific Gravity
Acetylene 0.0017
Air, dry 0.0013
Alcohol 0.82
Aluminium 2.70
Aluminium Alloy 356.0 2.68
Aluminium Alloy 360.0 2.68
Aluminium Alloy 364.0 2.63
Ammonia Vapor 0.60
Antimony 6.68
Balsa Wood 0.2
Barium 3.62
Barium sulfate 4.5
Boron 2.34
Brass 8.48
Calcium sulfate 2.96
Carbon 2.26
Carbon dioxide 0.00198
Carbon monoxide 0.00126
Cast iron 7.20
Caustic potash 2-044
Cement 3.15
Cerium 6.77
Cesium 1.873
Chromium 7.03
Citric acid 1.665
Clay 2.6
Copper 8.96
Depleted uranium 19.1
Diesel fuel 0.84
Epoxy resin 1.8 - 2.0
Ethanol 0.78
Gasoline 0.70 - 0.76
Glass 2.40 - 2.70
Gold 19.30
Grease 0.92 - 0.94
Hematite 5.26
Hydrogen 0.00009
Iron 7.87
Limestone 2.8
Melamine 1.8 - 2.0
Mercury 13.56
Natural Gas 0.59
Nickel 8.9
Nylon 1.12
Oak wood 0.75
Osmium 22.59
Oxygen 0.00143
Parrafin 0.80
Petrol (gasoline) 0.72
Phenolic 1.75 - 1.95
Platinum 21.5
Polyester 1.35 - 2.3
Polyurethane 1.11 - 1.25
Propane gas 1.55
PVC 1.36
Pyrite 5.02
Quartz 2.65
Rubber 0.96
Salt 2.165
Silicon 2.33
Soda ash 2.53
Sodium bicarbonate 2.16
Sodium sulfite 2.63
Steel, carbon 7.82
Steel, cold drawn 7.83
Steel, machine 7.80
Strontium 2.64
Sulfur 2.07
Table Salt 2.17
Tantalum 16.69
Tellurium 6.24
Terbium 8.27
Thallium 11.85
Thulium 9.32
Tin, pure 7.28
Titanium 4.506
Titanium, dioxide, Anatase 3.77
Tungsten 19.25
Tungsten, carbide 14.29
Uranium 18.7
Water 1
Water, sea salt 1.027
Ytterbium 6.97
Yttrium 4.47
Zinc 7.12
Zirconium 6.506
Zirconium silicate 3.85

## Universal Gravitational Constant

The universal gravitational constant ( $$G$$ ) is the proportionality constant used in Newton's Law of Universal Gravitation as shown above.

$$\large{ G = 6.67384 \; \left( 10^{-11} m^3 kg^{-1} s^{-2} \right) \; = \; 6.67384 \; \left( 10^{-11} Nm^2 kg^{-2} \right) }$$