+ Three forces of 20N, 90N and 30N are acting respectively on the left edge the middle and the right edge of a wooden bar of 100cm. Determine the resultant force of the three forces. .

Answer;

hot magma rises and pushes up toward the lithosphere, and as it cools it cycles back down toward the core to be heated again.

explanation; convection currents are the circular pathways taken by a fluid that enhances heat transfer by the process known as convection which occurs in fluids.convection currents transfer heat from one place to another by mass motion of a fluid. earth mantle is in a semi-liquid state and behaves like any other fluid, rising up from the bottom of the mantle after becoming hotter and less dense from heat of the earth's core, as the rock loses heat into the earth's crust it becomes cooler and more dense, then sinking back down to the core, then repeating the cycle.

The  asthenosphere  is now thought to play a critical role in the movement of plates across the face of earth's surface. according to plate tectonic theory, the lithosphere consists of a relatively small number of very large slabs of rocky material.

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