Institute for professional physicists. Members include college teachers, university lecturers, students studying to be physicists, Crown Research Institute scientists and industry scientists.

A group who represent professional physicists. News, membership information, details of conferences and meetings.

All of us know the mysterious force called gravity, holding us firmly onto Earth's surface. However, the question 'what is gravity' is not easy to answer at all. The reason is that we don't really understand what this force actually is (if it is indeed a force). What follows may give you a different way of thinking about gravity.

All objects resist being pushed around, even if there is little or no friction. Once an object is moving, it takes an equivalent amount of effort to stop it, i.e., to change that state of motion. This is a principle called inertia. More scientifically, inertia is the principle that an object will maintain its state of motion until acted upon by unbalanced forces, i.e. two or more forces that push against the object in such a way that they do not balance out.