For an explanation, see the main splats page

The principles of force in physics

• The four known and recognized forces of nature are the electromagnetic force, the gravitational force, the strong nuclear force and the weak nuclear force.

• The gravitational force exerted on a standard mass by an object depends on its mass, and on the square of the distance between their two centres of mass.

• The force of gravity obeys the inverse square law, and gravitational forces may be calculated using Newton's law of gravitation which is based on this.

• In 1674 Robert Hooke attempted to explain planetary motion as a balance of centrifugal force and gravitational attraction, but this failed to stand up.

• In 1665 Isaac Newton deduced the inverse-square gravitational force law from the 'falling' of the moon, rather than the apple of all the mythological accounts.

• In 1680 Isaac Newton demonstrated that the operation of the inverse square law on gravity leads directly to the formation of elliptical orbits in space.

• Gravitation is one of the four forces of nature. Although it may seem strong to us as we experience the force, it is a weak force which acts everywhere.

• In 1798 Henry Cavendish measured the gravitational constant with John Michell's torsion balance and from that, was able to determine the mass of the Earth.

• Based on the value of G and the known size of the Earth, Cavendish was able to estimate the density of the Earth at 5.48, close to the current value of 5.52.

• In 1749, Pierre Bouguer attempted to estimate the value of G, the Universal Gravitational Constant, using a mountain as an attracting mass, but it was too weak.

• The centrifugal force is a fictitious force, but there really is a force called the centripetal force. Either can be used in explanations and calculations.

• Under extreme conditions, the operations of gravity may lead to the formation of a black hole, a concentration of mass so great that even light cannot escape.

• Parabolic flight may be used to simulate 'weightlessness' near the Earth's surface, for short periods of time as an aircraft slows, turns over and falls freely.

• A centrifuge may be used to simulate high gravitational forces, relying on the accelerational forces used to keep rotating material moving in a circle.

• The understanding of the pendulum depends on understanding the forces involved, in particular, the restoring forces that operate in all forms of the pendulum.

This file is http://members.ozemail.com.au/~macinnis/scifun/, first created on February 18, 2009. Last recorded revision (well I get lazy and forget sometimes!) was on February 18, 2009.

©The author of this work is Peter Macinnis, who asserts his sole right to the product as it is packaged here, recognising that many of the ideas are common. You are free to use this as a model to do your own version. Copies of this whole file or site may be made and stored or printed for personal or educational use. You can contact me at macinnis@ozemail.com.au, but only if you add my first name to the front of that email address -- this is a low-tech way of making it harder to harvest the e-mail address I actually read.
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