All brass instruments (like trumpets and trombones) work by buzzing your lips. First, just practice buzzing your lips (hold your hand just in front of your mouth so you don't spread germs).
Then make a little tunnel with your hand and fingers and buzz your lips into the tunnel. You should get a nice, juicy "raspberry" or "Bronx cheer" sound. DON’T “SING” WITH YOUR VOCAL CORDS - THE ONLY THING VIBRATING SHOULD BE YOUR LIPS AS YOU PUSH THE AIR OUT. If you now increase the amount of air that is vibrating by pushing a tube to your lips you have a trumpet! Add a cone at the end to make it louder.
YOU WILL NEED:
Cardboard blowing tube (apx gift wrapping size and length)
File folder or plastic water, soda or juice bottle
Form the file folder into a cone shape. Make sure the narrow end can slip over the end of the tube. Tape the cone into shape, and then tape it to the very end of the tube. Or have an adult cut off the bottom of your bottle and then tape it to the end of the tube.
If the end of your tube is too wide, you can make it smaller by having an adult cut the top of a plastic bottle off and taping it securely to your tube.
Variation - If you have another tube that fits snugly inside the other but still slides freely, then you have a Tube Trombone!
You need to have just the right amount of seal between the tubes - not enough to impede the sliding of the tube, but enough to (in effect) increase the length of the air column as you slide the tube out.
HINT - you will get a better sounding pitch change if you also speed up your lips a bit as you make the tube shorter, and slower as you slide the tube out.
If the tubes don’t quite fit snugly you can wrap some tape around the inside tube to make a kind of primitive gasket.