Find a rock with a crack that can be filled with water. Put the rock with the water-filled crack into the freezer. After it has frozen completely, repeat the experiment until the rock eventually splits.
When water freezes, it expands and this will crack the rock into pieces. This occurs mainly in areas that are warm during the day and freezing at night.
Materials you need are:
vinegar or lemon juice (both are acids)
Pour the vinegar or lemon juice over the chalk and watch it disappear slowly.
Acid rain is formed when carbon dioxide and other gases from car and factory exhausts combine with rain. Acids can also be formed by decaying plant matter. Both of these weather or break down rocks as shown with the chalk.