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In addition to Gauss's law, the assumption is used that g is irrotational (has zero curl), as gravity is a conservative force: ∇ × g = 0 {\displaystyle \nabla \times \mathbf {g} =0} Even these are not enough: Boundary conditions on g are also necessary to prove Newton's law, such as the assumption that the field is zero infinitely far from a ...
Michael Foale can be seen exercising in the foreground. Weightlessness is the complete or near-complete absence of the sensation of weight, i.e., zero apparent weight. It is also termed zero g-force, or zero-g (named after the g-force) [1] or, incorrectly, zero gravity.
[18]: 14–15 The torque can vanish even when the force is non-zero, if the body is located at the reference point (=) or if the force and the displacement vector are directed along the same line. The angular momentum of a collection of point masses, and thus of an extended body, is found by adding the contributions from each of the points.
It is useful to notice that the resultant force used in Newton's laws can be separated into forces that are applied to the particle and forces imposed by constraints on the movement of the particle. Remarkably, the work of a constraint force is zero, therefore only the work of the applied forces need be considered in the work–energy principle.
For points inside a spherically symmetric distribution of matter, Newton's shell theorem can be used to find the gravitational force. The theorem tells us how different parts of the mass distribution affect the gravitational force measured at a point located a distance r 0 from the center of the mass distribution: [13]
In the case of a shock, e.g., a collision, the g-force can be very large during a short time. A classic example of negative g-force is in a fully inverted roller coaster which is accelerating (changing velocity) toward the ground. In this case, the roller coaster riders are accelerated toward the ground faster than gravity would accelerate them ...
For two pairwise interacting point particles, the gravitational potential energy is the work done by the gravitational force in bringing the masses together: = =, where is the displacement vector between the two particles and denotes the scalar product. Since the gravitational force is always parallel to the axis joining the particles, this ...
In addition to gravity, the shell theorem can also be used to describe the electric field generated by a static spherically symmetric charge density, or similarly for any other phenomenon that follows an inverse square law. The derivations below focus on gravity, but the results can easily be generalized to the electrostatic force.