How long would it take to fall through the Earth?
If you could fall through a tunnel straight through the Earth, with no air, you'd pop out on the other side in about 38 minutes.
Going deeper
The classic textbook answer, assuming the Earth has the same density all the way through, is about 42 minutes. A 2015 calculation using the planet's real, denser core gives about 38 minutes, because you'd speed up more as you fell toward the middle.
You'd hit top speed at the centre, then slow down as gravity pulled you back, arriving at the far side at a standstill. Without someone to grab you, you'd fall back and forth forever.