Consider the following statements:

1. In spur gears, the contact occurs abruptly on a line parallel to the axis, and the disengagement too is abrupt.

2. In helical gears, both loading and unloading are gradual, and therefore, these happen more smoothly and less noisily

3. When two gears mesh, any arbitrary shape of the tooth can be chosen for the profile of the teeth of any one of the two gears, and the profile for the other shall be obtained by applying the law of gearing.

Which of the above statements are correct?

Spur gears are used to connect two shafts when they are transmitting the power in a parallel direction. In spur gears when the teeth start getting engaged the contact between the teeth extends across the entire width on a line parallel to the axis of the rotation this results in the sudden application of the load, high impact stresses.

In helical gears the teeth are curved. In this gear, the engagement starts at the point of leading-edge only, therefore, loading and unloading are gradual and happen more smoothly and less noisily.