1. Thermal Expansion and Contraction:

* Ice expands when it freezes: Water expands when it freezes, which is why ice floats. This expansion creates internal stress within the ice.

* Liquid water contracts: Liquid water contracts as it cools.

* Temperature differences: When ice is in liquid water, the temperature difference between the ice and the liquid water causes the ice to contract and the water to expand. This difference in expansion and contraction creates stress on the ice.

2. Pressure Changes:

* Pressure from the liquid: The liquid water exerts pressure on the ice, further adding to the stress.

* Pressure from internal freezing: When water freezes within the ice, it expands, putting pressure on the surrounding ice.

3. Physical Properties of Ice:

* Brittleness: Ice is a brittle material, meaning it can't handle much stress before it cracks.

* Crystalline structure: Ice has a specific crystalline structure that can be disrupted by stresses, leading to cracks.

4. Impurities and Bubbles:

* Impurities: Impurities in the ice can create weak points where cracks can start.

* Air bubbles: Air bubbles trapped in the ice can expand as the ice warms, putting pressure on the surrounding ice.

How it all comes together:

The combination of these factors creates stress on the ice, which eventually overcomes its strength and causes it to crack. The cracks can start at weak points and then propagate through the ice, often in a branching pattern.

In summary: Ice cracks in liquid due to the difference in thermal expansion and contraction between ice and liquid water, the pressure exerted by the liquid and internal freezing, the brittleness of ice, and the presence of impurities and bubbles.