## Law of Universal Gravitation

Equation #9: Newton’s law of Universal Gravitation Probably the most familiar law in science which everyone seems to understand intuitively, the law of universal gravitation is one of the most powerful and useful equation for practical purposes. Before Newton, people

## Law of Inertia: First law of motion

Aristotle believed that the natural tendency of objects is to rest, unless there is some external push on them to keep them moving. e.g. if you give a push to a swing, it continues for some time and gradually slows

## Rigid body

A system of particles in which the interparticle distances rij are fixed and do not change in time. Hence, it retains its shape under the influence of external forces. Another way to think about a rigid body is a system

## Work

If there is an external force on a particle causing it to move in a certain direction by a displacement s, then there must be a component of that force acting in that direction and doing the work. This “work” is a

## Reference frames

Moving objects change their position over time with respect to a reference frame. By reference frame, we mean a set of directions(axes) and a reference point(origin). We should select a frame of reference in which Newton’s first law is valid