is that true a block on a flat surface. The normal force on the block and weight of the block make up a third law pair.

1 answer

Yes, if the surface is horizontal. They are equal in that case.

If there is an incline, the normal force on the block equals the component of the weight normal to the incline.

The block and the surface below it are ALWAYS a third law pair. They exert equal forces on each other.