Mahesh

We know that in Rutherford's atomic model expt. we use alpha-particles which are positively charged. When we bombard them on thin Gold foil we get following four observations as :

1) Most of the alpha-particles pass straight without any deflection from the Gold foil indicating that most of the part of the atomic must be hollow.

2) Few alpha-particles get deflected with obtuse angle from the Gold foil indicating that there must be something dense positively charged space at the center of the atom.

3) Very few appointments get deflected with an acute angle from the Gold foil indicating that there must be something dense positively charged space at the center of the atom.

4) Very very few alpha-particles get deflected with the phase reversal of 180° from the Gold foil indicating that the center of the atom which is positively charged must be very small as compared to the total size of the atom.

According to electrostatic law there is always repulsion between like charges & alpha-particles used in Rutherford's atomic model expt. are positively charged & get deflected each time there is repulsion between the alpha-particles & the central positively charged space hence there must be positively charged protons present at the central part of the atom i.e. nucleus must contain protons.

Actually coefficient of friction means friction between any two bodies without at rest. i.e. either one body is moving or both are moving in opposite direction. Formula : Force of friction = coefficient of friction . Normal Force

Therefore ,

Coefficient of friction = Force of friction / Normal Force

Hence , units get cancelled...

So, coefficient of friction is dimensionless i.e. unitless quantity...