When a body descends in air or another fluid, what determines its acceleration is the gravitational force minus the friction, not its mass.
If we hang a magnet by a thread, it always aligns itself in the same direction, even if there is no other magnet nearby. This is a compass and responds to the Earth's magnetism.
In the 17th century, it was difficult to achieve and maintain a partial vacuum. In the 21st century, the challenge is to achieve an ultra-vacuum in the laboratory such as we could never have dreamed of.
For there to be sound, there must be a vibrating source, a transmitting medium that propagates the vibration at a certain speed, and a receiver that is set into vibration when the wave arrives.
Using simple materials like plastic bottles, straws, modelling clay, and syringes you can witness many interesting phenomena relating to air and water pressure.
The historian of science Alexander Koyrè summarised the scientific work of the sixteenth century as a gradual understanding of the works of Archimedes.
Probably of Paleolithic origin and present since the first civilisations, the sling is ancient and ubiquitous not only as a weapon, but also as the paradigm of circular movement.
