Scale and a spider sac?
Both of these images look like different varieties of galls that are common on oak leaves. Oaks are hosts to several hundred different types of galls many of which are produced by tiny cynipid wasps (Family Cynipidae). Some of these galls have fuzzy coverings while others are smooth. Depending on the species of wasp, the galls may be on the upper surface of the leaves while others are on the under sides of the leaves. None of the leaf galls are of any great significance to the health of the trees. The second image looks like a common gall called the oak hedgehog gall (see this link for images: https://bugguide.net/node/view/425655