What you'll need:
You will also want plenty of space to move around as you levitate objects.
All materials are made of molecules that are composed of atoms (except for pure elements which are just atoms), which in turn are made of protons, neutrons and electrons. The electrons, which have a negative electric charge, are the smallest and most mobile of these sub-atomic particles and can easily move from one atom to another, even from an atom on one material to an atom on a different material. When two different materials, such as the latex balloon and the cotton or wool cloth, are brought very close to each other, the atoms in each material begin to tug at the electrons on the other, and the material which holds onto electrons the strongest may actually steal many of them from the weaker material once they are separated again. This gives the stronger material a lot of excess electrons, and thus a lot of excess negative electric charge, while the other material is left with an opposite or excess positive charge. This process is properly called contact electrification or triboelectricity, although it's more commonly referred to as static electricity. We can find triboelectric charts showing which materials steal electrons from other materials, i.e. which will become negatively or positively charged upon contact with another material in the chart, but triboelectricity can be finicky, so it's not always clear which way the electrons will go in all cases, and sometimes the behavior just doesn't agree with the chart at all.
Electrically charged materials create an invisible electric field or force in the space around them, which can attract or repel other charged objects (or electrons). Similarly charged objects (positive and positive or negative and negative) repel each other, while oppositely charged objects attract each other, sort of like the attractive and repulsive forces of magnets (in fact, magnetism is just another form of exactly the same fundamental force observed here- but that's for another activity). This is what's happening when you press the polyethylene plastic hoop against the tabletop surface, or rub the balloon with the cotton cloth. You have probably also noticed this if you ever rubbed a balloon on your hair. Rubbing them together just brings more of their surfaces closer together so that the atoms in one material can tug at the electrons of the other (it's not due to friction, so you don't need to rub hard). When you pull them apart you each will have opposite electric charge: the plastic hoop and the tabletop have opposite charge, i.e. one is positive and the other negative (that's why they cling or stick together); and the ballon or PVC and the cloth also have opposite charge, one positive the other negative. It can be very difficult to tell whether any particular object has a positive or a negative charge, but if the plastic hoop has the same charge as the balloon or PVC wand, whether it's actually positive or negative, they will repel each other (of course if they are oppositely charged they will instead attract and perhaps even stick to each other).
When you toss the plastic hoop in the air it starts to fall due to the pulling force of gravity, but your balloon or PVC wand can produce a pushing force on the hoop, and the closer you bring it the stronger that force will be. If you hold the balloon or wand at just the right distance below the hoop you should be able to make it levitate almost motionlessly- bring it closer and the hoop will rise, farther away and the hoop will fall.
Materials can also be classified as conductors if their electrons can move around easily through the material, or insulators if their electrons cannot move easily. Latex and Styrofoam are insulators, while metals such as the aluminum can are conductors. Thus when we charge the balloon by rubbing it, the charges stay put for a long time since their electrons can't easily move around. Metals are very different however. When we bring an aluminum can or a metal spoon near a charged object such as a balloon, electrons in the metal can move around easily. If the balloon has a negative charge, electrons in the pop can (which also have negative charge) move as far away from the balloon as they can, leaving a positive charge on the side of the can nearest the balloon, and since opposite charges attract each other, the can will move towards the balloon. The same thing happens when a metal spoon is held close to the balloon; if the balloon is hanging from a string and free to move, it will be attracted to the spoon. Your fingers are also conductors (though not as good as the aluminum in the pop can), so the balloon will also move towards your fingers or body. When a balloon filled with Styrofoam bits is charged (let's say it's negative), the bits will touch the balloon and acquire the opposite charge (positive) and stick to the wall of the balloon. Now when a metal spoon (or your fingers) is held close to the balloon, the side of the spoon facing the balloon becomes positively charged, and this positive charge (or the electric field arising from the positive charge) is strong enough to repel the Styrofoam bits (because they're are also positively charged), thus they jump way very quickly. Electric fields around conductors are also much stronger near sharp points and edges, thus as you turn the spoon (or point your fingertips), the Styrofoam bits will experience stronger forces and move more quickly.
Troubleshooting - What Can Go Wrong
Contact electrification or triboelectricity can be very finicky, often due to various types of contamination or environmental factors which can influence the process. Thus you might have trouble charging your objects, or even get the opposite of what you expect to see. Some days it just doesn't want to work at all, especially if it is a very humid day. Moisture in the air can deposit a thin layer of water molecules on some objects which allows the static electric charges to move away. Oil from your hands can also contaminate objects in this way, so if your plastic hoop doesn't seem to work , cut a fresh one.
In our experience rubbing a Latex balloon or PVC pipe with cotton cloth and rubbing a polyethylene bag on a wooden surface should produce the best results, but if these combinations don't seem to work for you, try something different. You can substitute wool, fur or polyester fabric for cotton, and you can try different wooden surfaces (painted, varnished, waxed, bare wood, etc.). Some kitchen countertops (like Formica) may also work very well.
In any case, the more you practice the better you will get at levitation, so keep experimenting. And who knows- a little Wingardium Leviosa probably couldn't hurt either!
Variations and Related Activities:
References and links to more information: