Talk with your kids and see if they can think of a few examples of things that slow down gravitational pull, or even appear to defy gravity. An obvious one is an airplane, which probably astounds many adults as to how a lump of metal can get off the ground. Another example that slows down the gravitational pull is a parachute, which enables the jumper to land on the ground as if he had jumped off a chair. Centrifugal force is another example and maybe something your kids have experienced at an amusement park. Once you've discussed the subject, see if you can replicate the effect using everyday objects in your home.
Cut out a 12-by-12-inch square and a 20-by-20-inch square from a lightweight plastic material, such as a garbage bin liner. This is the parachute project that reduces the pull of gravity. Cut eight pieces of 18-inch string. Tie the end of each string to a corner on the two plastic squares. Cut out two 6-by-6-inch squares from an aluminum-baking sheet using scissors and mold the squares into the shape of a basket. Carefully fold over any sharp edges so you don't cut yourself. You need to make the basket large enough so you can put an egg into each basket. Punch a small hole, using scissors, into the corners of the basket. Tie the opposite end of the string to the holes in the corners of the basket and then put an egg into each basket. Pick up the plastic square parachutes from the middle and hold them fairly high above you so you can drop them. Ask the kids whether they think the eggs will break, and which egg will land first. Write down the actual results.
Paper planes can be made from a couple of sheets of regular writing paper; the type you use to print from your computer is suitable. Make one that has wide flat wings like a fighter jet; these are called delta wings. The other is made so it has smaller wings, which look a bit more like a regular airplane. If you don't know how to make simple paper planes, there are websites with instructions (see the Resources section). Ask the kids which plane they think will fly the longest before landing. You can throw each plane several times, so you get a more accurate result. Write down the results.
Get a large wide-necked jar, such as the jars used for canning preserves, and a lightweight ball, such as a table tennis ball, which can fit inside the neck of the jar. The ball needs to be able to go inside the jar without touching the jar. Put the ball on the table and place the upside-down jar over the ball so it's sitting within the neck of the jar. Ask the kids whether they think you can lift up the ball in the jar without touching the ball. They will probably say it's impossible. Start spinning the jar around, while keeping it on the table; the ball starts to spin. When the ball is spinning quite fast, lift up the jar. The ball stays centrally inside the jar. Eventually the ball falls back to the table as it slows down.
Discuss the results of the projects with the kids. Explain how the parachute caught air inside while falling, which slowed down the descent; therefore, the gravitational pull wasn't so strong. The larger the parachute, the slower the descent since more air is trapped in the chute. The delta-wing plane flew farther because the wings had more air flowing over and under them, giving the plane more lift. The speed of the spinning ball in the jar created a force greater than gravity, enabling it to stay in the jar until the force of gravity was greater than the centrifugal force.