There is no way to know exactly when to bend it. It comes with practice and feel. The best approach is to heat the glass tubing gradually, and begin applying pressure while turning the tubing in the fingers to keep it rotating. Eventually, you will begin to feel the tubing "give", and in a second or two, it will bend.
Chat with our AI personalities
An object which does not bend is said to be rigid.
Some of the light is reflected off the glass at the same angle - in a manner and angle similar to that of a ball deflected off a surface at a similar angle. This is what happens when light reflects from car windows into our faces. Much of the light, however, will penetrate the glass, so that the light source is seen from the other side. Nevertheless, on contact with the glass, the light that penetrates will be refracted (bent) and travel through the glass at a different angle from that of its original contact with the glass; but once having travelled through the glass, it will leave at its original angle of contact. The amount of refraction depends on a number of factors, but especially, on the thickness of the glass and specific angle of contact involved. So, the light bends as it passes through the glass, but leaves at its original angle.
The reason for the pole appearing bent when put inside a glass of water is refraction. When a ray of light travels through one medium to the other, it tends to bend or deviate from its original path. Thus a light ray in this case, travels from the air through water, and then again through air and reach the eyes. Thus, the light ray deviates from its original path causing this phenomenon.
Ice will break rather then bend
when you crack your fingers, your fingers can't bend when you're older.