Final answer:
While all of Newton's Laws of Motion are involved in skateboarding, the most directly relevant to skateboarding on a road with obstacles is Newton's First Law of Motion. This law, which states that an object will keep moving at a consistent speed and direction until acted on by an external force, explains why a skateboarder keeps going until friction, gravity or a collision slows them down. It also explains why a skateboarder can be thrown forward when hitting an obstacle.
Step-by-step explanation:
All of Newton's Laws of Motion are relevant to skateboarding, even Newton's Law of Universal Gravitation. However, the most directly relevant is perhaps Newton's First Law of Motion.
The first law states that an object will remain at rest or move in a straight line at a consistent speed unless acted on by an external force. When you're skateboarding and not pedaling, you continue to move forward until friction, gravity or a collision with an obstacle slows you down and eventually stops you. This is known as inertia.
Similarly, once you're moving, if you hit an obstacle in the road and fail to steer around it, you'll be stopped abruptly and likely thrown forward due to your continued inertia. So, Newton's First Law of Motion is definitely relevant when skateboarding on a road with obstacles.
Learn more about Newton's First Law of Motion