Overview Gravity is the apparent phenomenon of objects with mass being attracted to one another and is observable to all objects with mass. While not as noticeable between smaller objects, it becomes very apparent with bodies of larger mass, such as a moon, planet, star, or galaxy. According to Einstein's general theory of relativity, it is a consequence of mass. In classical mechanics, it is described as a force acting between any two bodies with mass and is easily described using Newton's Law of Universal Gravitation, F=G(m₁m₂/r²). F is the force of gravity between two bodies, G is the gravitational constant 6.67408 * 10⁻¹¹m⁻³kg⁻¹s⁻², m₁ and m₂ are the masses of the two objects, and r is the distance between the center of masses of said bodies. Gravity can also be derived using the oscillation of a pendulum.
Because objects such as planets and moons have considerable gravity, it is also a major part of Orbital Dynamics. Earth's gravity also plays a major role in the physiology of living things, such as humans. The effects of microgravity in the short term include a range of side effects, such as muscle degeneration, weakened cardiovascular system, decrease in bone density, and an increase of fluids such as blood and cerebrospinal fluid higher up in the body where normally gravity would cause those fluids to be pulled downward in the legs. The effects of microgravity on humans in the long term are currently unknown. There are however various proposed ways to get around this issue.
Any object acting freely under the influence of gravity is said to be in freefall and will accelerate towards the center of mass between it and the body it is interacting with. Both objects will be pulled towards the center of mass. For something smaller such as gas, people, animals, or satellites the observable pull to the Earth's surface is quite noticeable. What's less noticeable is the pull smaller objects, such as gas, people, animals, or satellites have on the Earth. This is because the Earth's mass is significantly larger than the mass of said objects.
Gravity on various bodies in the Solar System
While the acceleration due to gravity, g, varies at different points on the earth depending on altitude, it is generally regarded as being 9.81m/s² downward to the surface, or -9.81m/s².
The acceleration due to gravity on other bodies of note are listed below:
- Venus = -8.87 m/s²
- Luna = -1.622 m/s²
- Mars = -3.721 m/s²
- Phobos = -0.0057 m/s²
- Deimos = -0.0039 m/s²
- Ceres = -0.27 m/s²
Impact on Manufacturing
The lower gravity on bodies such as that on Phobos, Deimos, or Ceres, poses a problem to manufacturing. Loose materials floating more freely pose a risk to both the removal of material from the ground and the manufacturing of raw material into a product. Because of this the movement of loose objects must be kept within a contained space, and be done much slower.