Jumping Jellyfish |
Newton's Laws of Motion
Newton's First Law of Motion
Passive Motion: When the jellyfish is engaged in passive motion, there are no horizontal forces acting on the jellyfish and, therefore, no horizontal motion. As the mass of the jellyfish increases, the magnitude of the unbalanced horizontal force that will be necessary to propel the jellyfish forward when it chooses to use active motion also increases. There is no vertical motion, as the positive 'y' force of buoyancy balances the negative y force of the force of gravity. The net force in the y-direction equals zero, and the jellyfish, disregarding the effects of currents, remains at rest.
|
Active Motion at a Constant Velocity: When the jellyfish is engaged in active motion and reaches the point of constant velocity in its motion 'arc', the forces acting on the jellyfish in both the vertical and horizontal directions are balanced. Vertically, the buoyant force balances the gravitational force. Horizontally, the thrust force balances the drag force. The net forces in the vertical and horizontal directions equal zero, so the jellyfish does not accelerate up, down, forward, or backward. Rather, it travels at a constant velocity.
|
Newton's Second Law of Motion
Acceleration: At the beginning of its motion 'arc', the jellyfish moves and accelerates in the same direction. The thrust force exceeds the drag force, creating an unbalanced force acting in the direction of motion. Acceleration is in the same direction as the unbalanced force, so the jellyfish accelerates forward. In the y-direction, there is no motion because the buoyant and gravitational forces remain in equilibrium.
|
Deceleration: At the end of its motion 'arc', the jellyfish's motion is opposite in direction to that of acceleration. The thrust force is no longer acting on the jellyfish; drag is the only horizontal force. Therefore, it is unbalanced. The net force is in the direction of drag and against the direction of motion. The jellyfish slows down and eventually reaches a stopping point. In the y-direction, the equilibrium of the buoyant and gravitational forces remain in equilibrium and do not cause any vertical motion.
|
Newton's Third Law of Motion
Force Pairs: The force pair relative to the aquatic locomotion of jellyfish is comprised of the jellyfish's force on the surrounding water, generated by its expelled fluid jet, and the counter-force of the water on the jellyfish. When the jellyfish pushes on the water behind it, the water pushes back with the same force and propels the jellyfish forward. The two forces are a force pair. As they are equal in magnitude and opposite in direction, they balance each other. The vertical forces acting on the water and on the jellyfish cannot be paired, as each object is affected by different forces in the y-direction. The force of earth and the force of the ocean floor act on the water, while the force of earth and the force of buoyancy act on the jellyfish.