There would be no seasons
Earth's axis is tilted to about 11 degrees from the vertical.
There would be no seasons, and the length of day & night would be exactly 12 hours each.
Gravity is always acting on the vertical axis, pulling objects downward towards the Earth's center.
Its axis
axis
The x axis is the horizontal axis. The y axis is the vertical axis.
The vertical axis is the y-axis. The horizontal axis is the x-axis.
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First of all, as long as we're in our comfortable familiar environment, "vertical" means toward or away from the center of the earth. When you start talking about things in space, the word "vertical" has no meaning. You might expect the earth's axis of rotation to be perpendicular to the plane of the earth's orbit around the sun. If that's what you expect, then you'll be disappointed. The axis of rotation makes an angle of about 66.5 degrees with the orbital plane.
The y axis is vertical and the x axis is horizontal.
The y-axis is vertical and the x-axis is horizontal.