Changes in speed
When an object is stationary it has an equal force pushing down and up. The downward force being gravity and the upward force being the surface the object is on. The object is not floating but it is not going into the ground.
When an object is accelerating it has the upwards and downwards forces but it also has forwards and backwards forces (drag and friction). The forward force is larger than the backward force when an object is accelerating.
When an object is going at a constant speed it has downward and upward forces as well as forward and backward forces. The forward and backward forces are equal, so the speed doesn't change even though the object is moving.
When an object is decelerating it has the equal upward and downward forces as well as forward and backward forces, but the backward force is larger than the forward one, slowing the object down.
Changes in shape
changes in shape affect momentum. Force= change in momentum/ time taken. An example of this is crumple zones in car decrease the force on the passengers.
Changes in direction
Which ever direction the force is greatest in will be the direction the object travels in.