# gravity

(noun)

## Definition of gravity

Resultant force on Earth's surface, of the attraction by the Earth's masses, and the centrifugal pseudo-force caused by the Earth's rotation.

Source: Wiktionary - CC BY-SA 3.0

## Examples of gravity in the following topics:

• ### Weight

• It is considered as the force on an object due to gravity.
• Mathematically, the weight of an object (W) can be found by multiplying its mass (m) by the acceleration due to gravity (g): $W=M\cdot g$.
• The strength of gravity varies very little over the surface of the Earth.
• In fact, the greatest percent difference in the value of the acceleration due to gravity on Earth is 0.5%.
• It is important to note that the apparent weight of an object (i.e., the weight of an object determined by a scale) will vary if forces other than gravity are acting upon the object .
• Weight is taken as the force on an object due to gravity, and is different than the mass of an object.
• ### Gravitational Potential Energy

• Gravitational energy is the potential energy associated with gravitational force, as work is required to elevate objects against Earth's gravity.
• An object at a certain height above the Moon's surface has less gravitational potential energy than at the same height above the Earth's surface because the Moon's gravity is weaker.
• Note that "height" in the common sense of the term cannot be used for gravitational potential energy calculations when gravity is not assumed to be a constant.
• Near the surface of the Earth, for example, we assume that the acceleration due to gravity is a constant g = 9.8 m/s2 ("standard gravity").
• Thus, when accounting only for mass, gravity, and altitude, the equation is:$U = mgh$where U is the potential energy of the object relative to its being on the Earth's surface, m is the mass of the object, g is the acceleration due to gravity, and h is the altitude of the object.
• Gravitational energy is the potential energy associated with gravitational force, such as elevating objects against the Earth's gravity.
• ### Center of Gravity

• Three-dimensional bodies have a property called the center of mass, or center of gravity.
• As seen in , it looks as if the external forces of gravity appear to be working only on the center of mass, but each particle is being pushed or pulled by gravity.
• The center of mass is much easier to use when discussing bodies, because no one has to analyze each individual particle.Mathematical Expression: The mathematical relation of center of gravity is read as: 'the position of the center of mass and weighted average of the position of the particles.'
• The center of gravity is read mathematically as: 'the position of the center of mass and weighted average of the position of the particles'.
• ### Variation of Pressure With Depth

• The pressure exerted by a static liquid depends only on the depth, density of the liquid, and the acceleration due to gravity.
• gives the expression for pressure as a function of depth within an incompressible, static liquid as well as the derivation of this equation from the definition of pressure as a measure of energy per unit volume (ρ is the density of the gas, g is the acceleration due to gravity, and h is the depth within the liquid).
• For many liquids, the density can be assumed to be nearly constant throughout the volume of the liquid and, for virtually all practical applications, so can the acceleration due to gravity (g = 9.81 m/s2).
• Thus the force contributing to the pressure of a gas within the medium is not a continuous distribution as for liquids and the barometric equation given in must be utilized to determine the pressure exerted by the gas at a certain depth (or height) within the gas (p0 is the pressure at h = 0, M is the mass of a single molecule of gas, g is the acceleration due to gravity, k is the Boltzmann constant, T is the temperature of the gas, and h is the height or depth within the gas).
• Pressure within static fluids depends on the properties of the fluid, the acceleration due to gravity, and the depth within the fluid.
• ### Gravity

• Gravitational energy is the potential energy associated with gravitational force (a conservative force), as work is required to elevate objects against Earth's gravity.
• If an object falls from one point to another point inside a gravitational field, the force of gravity will do positive work on the object, and the gravitational potential energy will decrease by the same amount.Potential Near EarthGravitational potential energy near the Earth can be expressed with respect to the height from the surface of the Earth.
• Gravitational energy is the potential energy associated with gravitational force, as work is required to move objects against gravity.
• ### The Relativistic Universe

• General relativity generalizes special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or space-time.
• In essence, gravity is a geometrical effect.
• Gravity is a geometrical effect in which a metric matrix plays a special role, and the motion of objects are altered by curved space.
• ### Tides

• Tides are the rise and fall of sea levels due to the effects of the gravity exerted by the moon and the sun, and the rotation of the Earth.
• ### Free-Falling Objects

• Galileo then hypothesized that there is an upward force exerted by air in addition to the downward force of gravity.
• If air resistance and friction are negligible, then in a given location (because gravity changes with location), all objects fall toward the center of Earth with the same constant acceleration, independent of their mass, that constant acceleration is gravity.
• The acceleration of free-falling objects is referred to as the acceleration due to gravity g.
• As we said earlier, gravity varies depending on location and altitude on Earth (or any other planet), but the average acceleration due to gravity on Earth is 9.8 m/s2.
• The kinematic equations for objects experiencing free fall are:$v=v_0-gt\\y=y_0+v_0t-\frac12gt^2\\v^2=v_0^2-2g(y-y_0),$where v = velocity, g = gravity, t = time and y = vertical displacement.
• ### Normal Forces

• By taking this angle into account, the magnitude of the normal force (FN) can be found from: $F_N = mg \cos(\theta)$, where: $m$ is the mass under consideration, $g$ is the acceleration due to gravity, and $\theta$ is the angle between the inclined surface and the horizontal.
• When the elevator goes up, the normal force is actually greater than the force due to gravity.
• The first is the force of gravity on the person, which does not change.
• By summing the forces and setting them equal to m*a (utilizing Newton’s second law), we find: $F_N - m\cdot g=m\cdot a$ where: FN is the normal force, $m*g$ is the force due to gravity, m is the mass of the person, and a is the acceleration.
• Since acceleration is positive, the normal force must actually be greater than the force due to gravity (the weight of the person).
• ### Key Points: Range, Symmetry, Maximum Height

• Projectile motion only occurs when there is one force applied at the beginning on the trajectory, after which the only interference is from gravity.
• As the projectile moves upwards it goes against gravity, and therefore the velocity begins to decelerate.
• Eventually the vertical velocity will reach zero, and the projectile is accelerated downward under gravity immediately.
• There is no acceleration in this direction since gravity only acts vertically.