|A wheelchair ramp is an example of an ____.
|An echo is an example of an acoustic (sound) ____.
|A cellular phone can receive and transmit ____ waves.
|The force that keeps the planets in orbit around the Sun is ____.
|Anything that takes up space (volume) and has mass is ____.
|The rate at which electrical energy is transmitted is ____.
|A seesaw is an example of a ____.
|Radio waves have a lower ____ than x-rays.