Relative density

The ratio of the density of a substance to that of the density of water is called relative density.

• Relative density = Density of a substance/Density of water

→ It has no unit as it is a ratio.

Kepler’s laws of planetary motion

Kepler observed that different planets take different time to complete one revolution around the sun. From s this observation of planetary motion he deduced that square of time period is proportional to the cube ob its distance from the sun.

Kepler’s First Law

Kepler’s first law of planetary motion states that planets move around the sun in such a way that sun always remains at one of its focus.

Kepler’s second law

 

According to second law the line joining planet to the sun sweeps out equal area in equal time interval, as the planet revolve around the sun in a elliptical orbit.

 Kepler's Third Law

It states that square of time period is proportional to the cube of its semi major axis.