Saturday, October 4, 2008

Inertia in Kayaking, Newton's 1st Law

This is a picture of the start of a kayaking race, all of the kayakers go from a position at rest to that of movement, meaning that they are providing a net force to overcome their inertia. The foot-wells of our kayaks have holes in them so that if water gets in them it can drain out as we kayak, however when we are at rest eh foot-wells just fill up with water because of the holes. I have always found it irritating that when we start kayaking too quickly from a rest position all of the water in the foot-wells rushes back into the seat area, rather than going out the holes in the foot-wells as it is designed to do. However at kayaking on Wednesday we were doing a workout that included starts, meaning that we had to go from a complete standstill to accelerating as fast as we would, and so of course every time we did a start all of the water from the foot-wells sloshed into our seats. It was at this moment that I suddenly realized it was inertia causing this to happen. Inertia describes the fact that an object at rest will remain at rest and an object in motion will remain in motion, unless acted on by a net force (Newton's 1st Law of Motion). When I am stopped in the kayak, my body, the kayak, and the water in the foot-wells are all at rest. However, when I abruptly start kayaking, I am applying a new force of the outside water, which in turn propels the boat and my body forward. Unfortunately, this net force does not act on the water in my foot-wells and so it stays at rest while the boat and myself move forward. Thus, it is not that the water rushes back into my seat when I start kayaking, but rather that my seat rushes forward to scoop up the water that is still at rest. When this realization suddenly hit me during practice I was pretty excited and I turned to my friend yelling, "its inertia!", but of course she had no idea what I was talking about or referencing. 

2 comments:

kohara said...

I get it! Kind of the same effect when you are holding a bottle of liquid up to your mouth while the car is at rest... then when your friend starts the car abruptly, the drink goes all over your face!

gavin said...

lol at mr. kohara's comment
but yeah i notice you write a lot about paddling!! haha lots of physics there...nice connection