Consider the following statements.

The form factor of a spur gear tooth depends upon the

1. Number of teeth

2. Pressure angle

3. Addendum modification coefficient

4. Circular pitch

Of the above statements

Explanation:-

The first analysis of gear-tooth stresses was presented by Lewis in 1892 - still used for gear-tooth bending stress analysis. 

The figure shows a gear tooth loaded as a cantilever beam, with resultant force W_N applied to the tip.

Mr. Lewis made the following simplifying assumptions:

The full load is applied to the tip of a single tooth.

The radial component, W_r, is negligible.

The load is distributed uniformly across the full face width.

Forces which are due to tooth sliding friction are negligible.

Stress concentration in the tooth fillet is negligible.

The Lewis form factor (Y) is based on diametral pitch, per Module, (m).

Y is the function of tooth shape (not size) and therefore varies with the number of teeth in the gear. Tooth shape includes addendum coefficient.

It is clear from the graph that the lewis form factor depends upon No. of teeth, and pressure angle.