And then there is the normal force perpendicular to the surface.

这个力，垂直于斜面。

youdao

I mean when I say up, of course it is still perpendicular to the surface.

当我说向上时，它当然仍是垂直曲面的。

youdao

And I will call this direction y, as I always do perpendicular to the surface.

照惯例把垂直方向，设为y方向。

youdao

The severity of the laboratory test was equivalent to an oblique collision with the rocky surface of the Earth - a comet coming in at an angle of less than 25 degrees from the horizon, rather than head on (perpendicular to the Earth's surface).

BBC: Comets could have seeded life on Earth

This is a special type of Earth model which traces its idealised "horizontal" surface - the plane on which, at any point, the pull of gravity is perpendicular to it.

BBC: Europe's Goce satellite probes Earth's gravity