Final answer:
When the lift force is greater than the weight of an airplane in flight, it will experience upward motion or climb.
Step-by-step explanation:
When the lift force of an airplane in flight is greater than its weight, the airplane will experience upward motion or climb. This is because lift is the force perpendicular to the direction of motion that opposes and overcomes the weight force acting vertically downwards. The excess of lift over weight allows the airplane to ascend or maintain altitude.