Teachers should lay a sheet of newsprint on a table where all students can observe the experiment. Dump 1/4 cup of cornstarch into a mixing bowl and set on the newspaper. Add 2 Tbsp. of water and stir until the powder achieves a stiff liquid feeling and appearance as you move your spoon through it. Ask a student to touch the cornstarch. Students will observe that the cornstarch immediately becomes hard, rather than splashing or squishing as one would expect a liquid to do. Scoop a spoonful into another student's cupped hands. Left alone, it will puddle in the child's palms, but if rubbed into a ball, it will stay solid as long as pressure is constantly applied.
Fourth grade students love science experiments they can eat after learning. Give each student a miniature marshmallow and a toothpick to insert as a skewer. Pour 1/2 cup of chocolate chips in a plastic bowl and microwave 1 minute. Students will observe the chocolate is in liquid form as it flows freely in the bowl. Each child should dip a marshmallow in the liquid chocolate and place on a sheet of wax paper. Teachers should place chocolate-covered marshmallows in a refrigerator to accelerate the phase transition from liquid to solid. After 3-5 minutes, students will observe the chocolate is in a solid state when they bite into the marshmallow.
Give each group a gallon-size freezer bag. Pour in 4 cups of crushed ice and 4 Tbsp. of salt. In a quart-size zip-close bag, combine 1/2 cup milk with 1/2 tsp. of vanilla and 1 Tbsp. of sugar. Double-seal the bag by slipping into a second quart-size bag and drop both into the gallon bag. Instruct students to seal the gallon bag and alternate between squeezing and shaking their baggies gently. Provide towels to prevent small fingers from freezing. After approximately five minutes, the liquid in the small baggie will solidify into vanilla ice cream the students will enjoy eating.
Prior to class, the teacher will need to collect grease by cooking hamburger meat or bacon and straining the liquid into a small container to a depth of 1/4 inch. During the experiment, heat the grease for 30 to 60 seconds so the grease turns to a warm liquid phase. Place the bowl in the refrigerator for about three minutes. Remove the bowl and tap the surface of the grease with a spoon. Students will observe the grease changes from liquid to solid based on temperature.