Talk with the children about the words that people use to describe gravity. Find different ways to describe invisible forces and other physics concepts. Use terms that are suitable for preschoolers, such as drop, fall, collide and bounce. Discuss what would happen if there were no invisible force. Understanding gravity means grasping that the invisible force pulls things down, and without that force, objects would float in the air. Tell a story about a morning when the invisible force has disappeared. Let the children come up with suggestion for completing the story. Prompt them by asking questions, such as: "What would happen when the girl gets out of bed?" or "What would happen when she tries to brush her teeth?" Ask children to illustrate the story.
Building towers is a fun way to learn basic principles behind gravity. If you put larger blocks on smaller blocks and there is too much force, the tower falls. Ask the preschoolers to construct bridges and see what happens when they put different objects on the bridges. Talk about how a real bridge must be sturdy enough to support both its own weight as well as people walking or driving on it. Construct bridges in different materials, such as building blocks and cardboard balanced over a couple of blocks. Let the children put different objects on the bridges, and see how many things you can put on different types of bridges.
Bouncing balls in the playground can help children learn about gravity. Ask the children to bounce balls in different ways and see how the force that the children use influences the height of the bounce. Drop balls and watch how they bounce to a lower height; talk about what you need to do to keep a ball bouncing. Ask one child to hold her hands at the level from which the ball is dropped. Let another child hold his hand at the level of the first bounce. Compare the levels and drop the balls a couple of times to see if you can change the level of the first bounce by pushing the ball harder.
Tell children that gravity is what keeps their feet on the ground and that the invisible force varies on different planets. Let them describe what it would feel like to walk on a planet with more invisible force and one with less. The gravity on the moon also is less than on Earth, so astronauts could bounce on the moon. Let the children walk around the room pretending that they are walking on different planets. The gravity on Jupiter is two and a half times that on earth, so it would be extremely difficult for people to walk on Jupiter.