in the time it takes blob to move 1 step, flash runs around and shakes all muscles soo much that he burns off all the fat and the blob becomes skinny...
Rubber materials can slowly spread out the force of vibration over a larger area, thus limiting its effectiveness. Given that the Blob is grounded (and grounded well) the energy would be transfered to the ground, where Flash lives!
You're assuming Flash is capable of a limitless strength punch aren't you? He may be able to channel a lot of this "speed force" but even Flash has a limit. Besides, let's say he channels the force the depth of his arm into Blob. What is that... 2 2.5 feet? His belly will just overlap the force exerted in that area.
Fine, let's assume almost infinite mass.. not INFINITE. His arm would still find itself 2 feet into fat... which would quickly bounce back into shape. Like magic!
"The Blob's body has several unusual properties in itself. The first is its superhuman resistance to injury. The fat tissues that comprise the Blob's epidermis are able to absorb the impact of rifle bullets, cannonballs, bazooka, and even torpedoes. The larger of these projectiles recoil from his body at one half the force of impact. The smaller one imbed themselves in his layers of fat tissue, enabling him to eject them by merely flexing his muscles. The Blob's nerve endings do not relay any tactile perception to his brain which are near the threshold of pain. The fat tissue of his epidermis is resilient enough to revert to its normal shape after deformation caused by impact. It is virtually impervious to physical injury. The Blob's skin cannot be punctured, lacerated, frostbitten, or ravaged by any skin disease, due in part to the skin's greatest elasticity and toughness and in part to the highly accelerated rate at which his skin cells grow and replace themselves. His skin is somewhat less resistant to burning.
It is not yet known if there is an upper limit to the Blob's ability to absorb impact. While he could easily survive a head-on collision with a bus traveling at a hundred miles per hour, even a highly ferrous meteorite fifty feet in diameter on top of him at terminal velocity, it is not known whether he could survive a collision with an object traveling at near light speed. Further, it is not known whether his skin's imperviousness to heat could survive the 11,000,000-degree heat at ground zero of a multi-megaton atomic blast."