Newtons Laws |
An explanation how each of Newtons Laws relates to and is manifest in a volleyball serve |
Newtons three laws of motion
Issac Newton established 3 basic ideas that are applied to the physics of most motion. Over the years, these ideas have been tested and verified countless times, thus scientists call them Newtons three Laws of motion. These physical laws form the basis for classical mechanics and describe the relationship between the forces acting on an object and that objects motion due to those forces. Newtons Laws affect every aspect our our life, therefore they affect a volleyball serve as well.
Newtons First law of motion
Newtons first law of motion, also known as the Law of Inertia, states that: an object at rest stays at rest and an object in motion stays in motion with the same speed and direction unless acted upon by an unbalanced force. Somewhat intuitive, but we can break this law down into its two components and relate it to a volleyball serve. First lets consider the statement: an object at rest will remain at rest unless acted upon by an unbalanced force. Try as you may, the volleyball will not go anywhere unless a player serves it over the net. Now consider the other aspect addressed in the law: an object in motion will remain in motion in a straight line at a constant speed unless acted upon by an unbalanced force. Without gravity, a volleyball serve would theoretically continue in one direction at a constant speed forever. On Earth however, it is apparent that the ball begins to fall towards the ground shortly after it is served. This of course is due to gravity, the aforementioned unbalanced force (in this case). As the ball begins to arc down towards Earth due to gravity, it is possible that an opposing player will pass the ball before it hits the ground, and thus the direction and speed of the ball will change. This change is made possible only through the presence of an unbalanced force (the opposing player).
Newtons second law of motionNewtons Second Law of Motion can be stated as such: the acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. Newtons Second Law is mathematically represented as: Fnet =
m x a. Net force is also referred to as the sum of the forces or ∑F. In the most basic sense, Newtons second Law is very apparent in a volleyball serve. The mass of the volleyball does not change during a given match, thus the magnitude of the acceleration is due solely to the force applied to the ball by the server. The harder a player hits the ball, the faster it will go in whatever direction it was hit. If the ball is not hit hard enough (ie. the applied force is not great enough), then the ball will not go over the net. Similarly, if too much force is applied and the ball is hit too hard, the ball will travel out of bounds. As mentioned however, there are forces that oppose the force applied by the server. Remember it is the sum of the forces that is important. Air resistance or drag opposes the motion of the volleyball and is a friction force, hindering the forward motion of the ball. This makes the net force on the ball in the x direction less than the applied force as mathematically, you are adding a negative force (drag) to a positive one (applied) to find net force. Additionally, the force from spin affects the motion of the ball and thus it will be represented in our FBD. For our purpose, it is simpler conceptually to imagine the force of gravity as the only significant force in the y direction affecting the volleyball.
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Newtons third law of motion
Newtons third Law of motion states, for every action, there is an equal and opposite reaction. Forces always come in pairs, there are action and reaction forces. Any volleyball player will attest to the legitimacy of this statement. When a player hits the volleyball, in a serve or spike, the ball hits the player's hand with equal force. Newtons third Law is also experienced during a jump serve, as the player applies a force on the ground, the ground exerts and equal and opposite force back up, allowing the player to go airborne. Similarly, Newtons third Law is seen in the passing of a serve by the opposing team. The action force in this case is the force of the volleyball hitting the forearms of the passer and the paired reaction force in the force of the passer on the ball. To the right is a video example of the usefulness of Newtons third Law in a volleyball spike. The man hitting, Leonel Marshall, plays for the Cuban national team and has a recorded vertical jump of ~50 inches.
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