A skateboarder pushes off from a standstill and accelerates along a flat, level surface. After a few seconds, the skateboarder stops pushing and travels at a constant speed. Eventually the skateboarder comes to rest. Describe and explain the forces acting on the skateboarder during each of the three stages of the journey.

During acceleration the skateboarder exerts a forward push on the board; this push force (the driving force) is larger than the resistive forces of friction and air resistance, giving a net forward force that causes acceleration.

At constant speed the push force is no longer applied. The only horizontal forces are friction and air resistance, which are equal and opposite, so the net horizontal force is zero and the speed remains constant.

When the skateboarder stops pushing, the resistive forces of friction and air resistance act alone. They act opposite to the direction of motion, producing a net backward force that decelerates the board until it comes to rest.