A grain of sand
yes
Large, heavy materials such as boulders or gravel are least likely to be carried in suspension because they require more energy to keep them moving in the water column. Instead, these materials tend to be transported as bed load, rolling or sliding along the riverbed.
Large boulders and smaller rocks can be carried by a river. When rocks and sediment are displaced, it's called erosion.
Because they are not usually power assisted, and in a strong wind it's hard to steer.
The sailboat appears to be sinking due to the weight of the water it has taken on, possibly from a leak in the hull or other damage that has compromised its buoyancy. The water entering the boat is causing it to become increasingly heavy and unstable, eventually leading to it tipping below the waterline.
I believe it was Thor.
Yes.
Coal
no
A large fir tree which was being carried by Rubeus Hagrid into the Great Hall as a Christmas decoration.
rucksack