For an explanation, see the main splats page

The principles of dynamics in physics

• Raising an object against gravity increases its potential energy, which can be recovered by letting it go, when the potential energy becomes kinetic energy.

• Mass and weight are different: objects in free fall have no weight, but they still have mass, and strictly speaking, they are weightless but not massless.

• Every solid body which has mass has a centre of gravity, a point which sometimes lies outside of the body itself, if the body has an irregular shape.

• When a force operates on a body, it accelerates. This is a change in velocity, involving either speed or direction, so moving in a circle is acceleration.

• Aristotle believed that if a small stone and a large stone were dropped from a tower, the large stone would fall faster than the small stone, which was wrong.

• Around 1350, Jean Buridan and Nicolas Oresme said, contrary to Aristotle, that unequal masses would fall at the same speed, as Galileo Galilei argued later.

• Galileo Galilei may have dropped rocks of different sizes, but also described what we would now call a perfectly good thought experiment to give the answer.

• In 1604 Galileo Galilei showed that the distance travelled by a freely falling object increases as the square of time during which it has been falling.

• Velocity is a vector quantity with both a speed and a direction, so acceleration may involve a change in either or both. Circular motion is accelerated.

• The study of flight is called aerodynamics. Flight depends on the interactions of forces produced by solid surfaces moving with respect to the atmosphere.

• The law of conservation of momentum describes what happens when moving bodies interact in a collision, the main effect being that momentum is conserved.

• Much of modern technology depends on devices that convert energy from one form to another. Usually one of those forms is electrical or chemical.

• All movement is subject to three laws called Newton's laws of motion which relate velocity, force, time, displacement, acceleration and mass to each other.

• Newton's 1st law: Every body continues in a state of rest, or uniform motion in a straight line, unless made to change that state by forces impressed upon it.

• Newton's 2nd law: The change of motion is proportional to the force on it, and is made in the direction of the straight line in which the force is impressed.

• Newton's 3rd law: To every action there is an equal and opposite reaction; the mutual actions of two bodies on each other are equal, and directed opposite ways.

• The process of adding vectors to one another may be carried out with the parallelogram of forces, or mathematically, whichever is more convenient.

• Perpetual motion is physically impossible, mainly because of frictional losses in moving parts and the transfer of energy to air surrounding the machine.

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.

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