That seems pretty slow, but, considering the size of the continent, the force of that movement can be huge. If a bicycle moved an inch and bumped into you, it wouldn't really hurt. If a car moved an inch and bumped into you, it might make a bruise. If a school bus moved an inch, the bump might break a bone. If a tractor trailer bumped into you, you'd notice.
Scientists think that the entire crust of the Earth is broken into big pieces called plates.
All of the plates are drifting on the liquid molten magma of the mantle beneath the crust. Even though they're drifting very slowly, when they bump into each other, the force is huge. People who live near the edges of a plate notice the bumping. Most often, the earth beneath them quakes and shakes as the plates bump and rub. Scientists call this action plate tectonics.