Old Opportunity Mars rover makes rock discovery

Nasa's ageing Opportunity rover on Mars has just made what may be one of its most significant discoveries to date.

The nine-year-old robot has identified rock laden with what scientists believe to be clay minerals.

Their presence is an indication that the rock, dubbed Esperance, has been altered at some point in the past through prolonged contact with water.

Newton's first law

Newton's first law of motion is often stated as

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Forces

Forces

One of the basic features in physics is the occurrence of forces that keep matter together. There are for example, the forces that keep the cells together to build up the human body, and there is the gravitational force that keeps us on the ground and the moon in orbit around the earth. We can ourselves exert forces when we push something and, by engineering, get some of the energy content in oil to 

Relativity: The Special and General Theory by Albert Einstein

A. EINSTEIN
Part I
The Special Theory of Relativity
Physical Meaning of Geometrical
Propositions
In your schooldays most of you who read this book made acquaintance with the noble
building of Euclid's geometry, and you remember — perhaps with more respect than love
— the magnificent structure, on the lofty staircase of which you were chased about for
uncounted hours by conscientious teachers. By reason of our past experience, you would
certainly regard everyone with disdain who should pronounce even the most out-of-the-way
proposition of this science to be untrue. But perhaps this feeling of proud certainty would