Of course to do this you can only do this if you ignore certain physical laws. If it was a hole through the actual Earth your acceleration would increase for the first half of the trip until you hit the core/mantle boundary at which point you would be accelerating at about 10.8 m/sec^2 if there is a vacuum in the hole. Now if there is air in the tube the pressure will go up until the air is no longer a gas, it would be a supercritical fluid. If the hole was man sized it will not hold a significant fraction of the Earth's gravity. So let's put magic baffles in the tube. We already have magic sides that keep the heat out and stand up to amazing pressures so a little more magic can't hurt. You will fall at terminal velocity the whole trip down and never quite reach the center.