gravity

(noun)

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.

Related Terms

Examples of gravity in the following topics:

  • Center of Gravity

    • The center of gravity is read mathematically as: 'the position of the center of mass and weighted average of the position of the particles'.
    • 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.
    • 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. '

  • 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 $\displaystyle \frac{m}{s^2}$.
    • This value is also often expressed as a negative acceleration in mathematical calculations due to the downward direction of gravity.

  • Gravity

    • Gravitational energy is the potential energy associated with gravitational force, as work is required to move objects against 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.

  • Weight

    • Weight is taken as the force on an object due to gravity, and is different than the mass of an object.
    • It is considered as the force on an object due to gravity.
    • 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%.
    • Infer what factors other than gravity will contribute to the apparent weight of an object

  • Defining Graviational Potential Energy

    • Gravitational energy is the potential energy associated with gravitational force, such as elevating objects against the Earth's gravity.
    • Gravitational energy is the potential energy associated with gravitational force, as work is required to elevate objects against Earth's gravity.
    • 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 $g = 9.8 \text{m/}\text{s}^2$ ("standard gravity").
    • Thus, when accounting only for mass, gravity, and altitude, the equation is:

  • Variation of Pressure With Depth

    • Pressure within static fluids depends on the properties of the fluid, the acceleration due to gravity, and the depth within the fluid.
    • 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).
    • This equation 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).

  • Weight of the Earth

    • Furthermore, inside a uniform sphere the gravity increases linearly with the distance from the center; the increase due to the additional mass is 1.5 times the decrease due to the larger distance from the center.
    • Thus, if a spherically symmetric body has a uniform core and a uniform mantle with a density that is less than $\frac{2}{3}$ of that of the core, then the gravity initially decreases outwardly beyond the boundary, and if the sphere is large enough, further outward the gravity increases again, and eventually it exceeds the gravity at the core/mantle boundary.
    • The gravity of the Earth may be highest at the core/mantle boundary, as shown in Figure 1:

  • Normal Forces

    • 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.
    • 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. shows the line of range.
    • The range of a projectile motion, as seen in this image, is independent of the forces of gravity.

  • Gauss's Law

    • Gauss's law has a close mathematical similarity with a number of laws in other areas of physics, such as Gauss's law for magnetism and Gauss's law for gravity.
    • In fact, any "inverse-square law" can be formulated in a way similar to Gauss's law: For example, Gauss's law itself is essentially equivalent to the inverse-square Coulomb's law, and Gauss's law for gravity is essentially equivalent to the inverse-square Newton's law of gravity.