Why does a boat sink lower when people climb in?

Have you ever stepped into a little boat on a lake? You may have felt it wobble and dip under your feet. The boat went down into the water as you climbed aboard. Why does a boat sink lower when people climb in?

Every boat on the water has a line where the water touches its side. That line is the waterline, which means the place where the water stops on the boat's side. On an empty boat, the waterline sits close to the bottom.

Water pushes up on the bottom of every boat. That push from below keeps the boat floating. It works like your hand holding a ball up from underneath.

The boat pushes down on the water with its own weight. An empty boat is light, so the water's push holds it up high. Most of its side stays up in the air.

Now people climb into the boat. Each person makes the boat heavier. So the boat pushes down on the water much harder than before. What do you think happens to the waterline now?

The boat slides deeper into the water. The waterline creeps up the boat's side, closer to the top edge. The water now covers more of the boat.

As the boat goes deeper, it pushes more water out of the way. So the water all around it pushes back up on the boat, harder than before.

Soon the water's push grows strong enough to hold the heavier boat. The boat stops going down and keeps floating, just lower in the water.

Today's special word is waterline. People make the boat heavier, so it pushes down harder and sinks deeper.

Thank you for wondering about boats today, and sweet dreams of calm, gentle water.