The Metric, and the US Standard systems. :)
This is easily explained saying that the frictional force between the books and the paper isn't big enough to produce a displacement in the books. The displacement in the books doesn't happen because the frictional force between the books and the surface they are standing on is bigger than the paper's one.
Answer:
The answer is "No, Hoverboards are risky, and riders are in danger of falling".
Explanation:
It's also known as a self-balanced scooter, it handheld electrical devices traveling on two wheels are hoverboards. It dominated the industry around 2015 and since then has become more and more successful. A rider is balanced on a frame between these wheels, driven by battery-powered lithium-ion batteries.
If the girl is also near the source of the sound, two alike sets of sounds will be heard.
your answer would be The one in the top right corner that looks a bit like this..
