Idiom of the Day
full of hot air
to be full of nonsense, to be talking nonsense
I knew that the man was full of hot air when he began to tell us how to make lots of money.
Science Experiments Ideas
Push two pencil leads through the short sides of a matchbox, just above the base. Scrape off some of the surface, and do the same with a shorter lead, which you lay across the top. Connect the microphone with a battery and earphone in the next room. You can take the earphone from a transistor radio. Hold the box horizontal and speak into it. Your words can be heard clearly in the earphone.
The current flows through the graphite leads. When you speak into the box, the base vibrates, causing pressure between the leads to alter and making the current flow unevenly. The current variations cause vibrations in the earphone.