Student: Normally there is a perception that, "speed kills" and that high speed is dangerous. But, planes fly at high speed and are generally considered safe. So, how do you address this paradox?
Teacher: It all depends on the context. So, sometimes high speed can be dangerous but sometimes high speed is desired. In fact, sometimes high speed is essential. A very common case is that of circular motion. Consider an electron moving in a circular orbit in the Bohr model of the hydrogen atom.
Electrostatic force, $\frac {k.e.e}{r^2}$ = centripetal force, $\frac {mv^2}{r}$
So, $v = e \sqrt \frac {k}{rm} = 1.6\times 10^{-19} \sqrt \frac {9\times 10^9}{0.53\times 10^{-10}\times 9.1\times 10^{-31}}$
$= 1.6\times 3\times 10^{-19} \times 10^{24} \sqrt \frac {1000}{48.23}$
$\approx 4.8\times 10^5 \times \sqrt {20.73}$
$\approx 4.8\times 10^5 \times 4.55$
$\therefore v \approx 2.18 \times 10^6 m/s$
Which is a phenomenal speed. So, despite such a high speed the atom is reasonably stable. A stable atom makes the existence of molecules possible which in-turn make the complex living world. Right now, we are moving at a very high speed because Earth is rotating on its axis and revolving around the Sun. Imagine what would happen if the orbital speed of Earth around the Sun suddenly became zero.
Of course, excessive speed can be dangerous in many situations. The point is that speed cannot be judged in isolation; its consequences depend on the context.