Thousand pound safe! Light as feather.
Try about 2 1/2 tons of bricks, in the back of an old landie. On the way back from builders merchants, at a sensible speed ~20 mph. Tried stopping on a very muddy road. I tried and failed.I stopped quite well after going through the hedge and wall. Broke a headlight as well. Being a landie though, into reverse, finish last mile home a bit slower, unload and go round to say sorry.
Now that's inertia in action.