I have to agree with the general tone of the answers. Whips are a very variable instrument. Even a harsh whip, used gently is not that hard to endure, while a relatively light and soft whip can still be quite painful if applied as hard as possible targeting the sensitive and intimate places of the female's body. Of course there are extremes, the very soft very multi-tail 'floggers' sold as BDSM toys are designed so they really don't hurt no matter how hard someone tries. The other extreme is the 'flagellum' the loaded Roman whip which was designed specifically to flay a person alive. But as someone already pointed out, we can't/ won't go there for fun and games.
What has not been mentioned so far, is the effect of the length of the whip. The longer the whip, the faster the tip can/will fly. In fact, the "crack" of the whip, is the sound of the tip breaking the sound barrier (343 meters per second, 1125 feet per second). And needless to say, any object hitting a nude female body at that speed will do serious damage. But there has to be a certain length to a whip before it can be 'cracked'. Bullwhips are known for this, but that is because they are traditionally 12 - 16 feet long (long enough to reach the front animals of a 4 to 6 horse or oxen team). Which does bring us to one other point ('trick'). If, for a film for example, you want to hit someone with a bullwhip, but don't want to do damage, and/or extreme pain, the whip can be used so when it is fully swung, the middle part of the tail hits the subject and then the whip curls around her body. The middle part will not be traveling that fast, and the tip will slow down as it curls around. Done 'right' for cinematic effect, this can even be done so the tip never actually makes contact with the subjects body.
On the other hand, for a real whipping, the whip-master/mistress will use the whip so the tip of the tail strikes the subjects body directly. That is what extracts maximum pain. But for whipping a human, that needs to be done with a relatively short whip - 3-4 foot tail. Maybe at most 6 feet. And of course, all braided whips have a 'stinger' at the end too, a knot that prevents the braid from unraveling during use, but which, as the nicknames makes clear, also 'stings' very nicely.
In the interests of 'full disclosure'; I have been seriously whipped three times.