Mostly when your around carpet or anything related to a carpet because when you do it long enough you will generate static electricity i hope this helps
The source and the observer are moving towards each other. The observer is moving toward the source. The source is moving away from the observer
Wavelength can be calculated using the following formula: wavelength = wave velocity/frequency. Wavelength usually is expressed in units of meters.
Well we have two concepts of gravity now. In Newton's concept masses create forces between them. In Einstein's concept mass distorts time and space around it and makes masses move as if there are forces between them.
So whichever concept you prefer it's the presence of mass that creates gravity.
