How to use: A crate sits on a floor. Push shoves it right,
Pull tugs it left, Friction says how slippery the floor is, and
Mass is how heavy the crate is. Press Release to let go. The net
force is the push and the pull added together, less the friction; divide that by
the mass and you get the acceleration (Newton's second law). A push too small to
beat the floor's grip does nothing at all. Once it is moving, forces that balance
leave the speed alone, a force along the motion speeds it up, and a force against
the motion slows it down (first law). Drag the crate on the canvas to shove it by
hand, or focus the canvas and use the arrow keys.
Notice: it is the net force, not the push on its own, that sets the
acceleration. Raise friction and a big push can leave almost no net force at all —
which is exactly why a bookcase will not move no matter how hard you lean on it.