The weapons she needed were oars, and these were lying out in plain sight on the boat's simple plank benches. She tried to snatch one up and was dismayed to find it was twice as long as she was tall, too heavy and unwieldy to be snatched; but at any rate she heaved it up off the benches and rotated its blade down into the water. Standing in the stern, where the water under the keel was shallowest, she stabbed down through the surf and into the firm sand. The longboat was reluctant to move, and one who had not recently familiarized herself with the contents of Isaac Newton's Principia Mathematica might have given up. But the elemental precepts of that work were certain laws of motion that stated that, if she pushed on the oar, the boat had to move; at first it might move too slowly to be perceived, but it had to be moving. Eliza ignored the unreliable evidence of her senses, which were telling her that the boat was not moving at all, and pushed steadily with all her might. Finally she felt the oar's angle change as the boat moved out from shore.