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.