Why Did the Water Rise?

It can look as though the glass is somehow sucking the water upwards.

But the glass isn't pulling the water in.

The answer involves something we cannot see — air pressure.

What Happens to the Air?

While the candle is burning, it heats the air trapped inside the glass.

Warm air expands, and some of it can escape underneath the edge of the glass. You may even have spotted tiny bubbles escaping as you lowered it.

After the flame goes out, the air inside begins to cool.

Cooling air takes up less space, and water vapour produced by the flame can also condense into liquid water. Together, these changes cause the pressure inside the glass to decrease.

So What Pushes the Water Up?

The air outside the glass is still pushing down on the water with atmospheric pressure.

Now the pressure outside is greater than the pressure inside the glass.

That pressure difference pushes water underneath the rim and up into the glass until the pressures become more balanced.

So the glass doesn't really “drink” the water at all.

The surrounding air pushes it in.

Scientists Say…

Air may be invisible, but it has mass and exerts pressure.

When the pressure on two sides of something is different, air pressure can produce surprisingly large forces.

The same big idea helps explain suction cups, drinking straws, syringes and even some weather patterns.

Curiosity Spark

Would a taller glass make the water rise higher?

What about using two candles instead of one?

Make a prediction before you test it.

Try these

[Feed the Monster].

 [The Magic Water Cup]