Newtons Laws of Motion - Essay Example

Newton's Laws of Motion Sir Isaac Newton, born in 1642, is recognized as the greatest physicist of all time. He gave first introduced Newton's laws of gravitation in 1666 and then after two decades he came up with the renowned Newton's laws of Motion in 1686. he presented these lawn in his book "Philosophiae naturalis principia mathematica (Mathematical Principles of Natural Philosophy)". The three laws of motion describe the movement of physical objects. These laws help clearing the understanding of many results previously presented by other scientists and physicists. Newton's First Law of Motion Newton's First Law of motion is also known as law of inertia. The law states that: Any physical object which is at rest will remain at rest until an external and unbalanced force is applied to it which will cause it to move and a body in motion will continue to be in motion with the same speed unless an external unbalanced force is applied to accelerate, decelerate or stop its motion. Or An object continues its state of motion unless an external unbalanced force is applied to change its state. Several things are needed to be defined to understand this law. Firstly we talk about inertia. Inertia is an ability of matter to resist any change in its motion. For example when a person is sitting in a bus, he is moving with the same speed as that of bus. If brakes are applied suddenly by the bus driver, it is the inertia of a person's body that pulls him forward. The second thing that is important to understand is the concept of Net forces. A net force is the vector sum of all the forces being applied on a body. For example if two forces, each of 10 N, are applied on a body, one from the top and one from bottom then the body will not move in any direction. Since these forces will cancel out each other's effect and the net force on the body will be zero. Now if an object experiences any net force greater than zero it will change its state. A very common day example of this can be a car moving on an empty road. If you turn off the engine, the car will move to some distance and then stop. What is the reason behind this The car when moving is experiencing a force from its engine and some other forces such as friction from the road and air resistance. The car needs sufficient driving force from engine to counter the effects of air resistance and road friction. When the engine is turned off, the car will move because of the momentum it gathered due to its motion for some distance but a net force opposite to its direction of movement are being applied by road and air which will slow it down and will ultimately stop it. Same goes with a cold drink glass in a glass holder kept in a moving car. If a car is moving with the speed of 70 km/hr without any speed breaker and considering that the road is all smooth, the cold drink will not spill out of the glass but it will spill out in case of application of sudden brakes. The reason is simply that when the car was moving with a constant velocity, the drink in the glass was also moving with the same speed and in the same direction as that of car. But when brakes were applied suddenly and car stopped the drink still continued its motion which causes it to spill out of the glass because the force was applied to the wheel of the cars to stop them and not to the coffee. So, when no external force was applied to the drink it continued its motion till it spilled. In our everyday life we do many things that are good examples of First law of motion. Such as a carpenter or a wood worker: when he feels that the head of hammer has loosen its place from the wood of hammer, he hold the hammer from the middle and bangs its bottom on a hard surface to tighten it to its place. The phenomenon behind this is when he moves hammer at a fast speed downwards, every part of hammer is moving with it, but when the bottom hits the surface, still the head of hammer is moving with the same speed downwards and due to this it fixes itself on hammer. (Henderson T. 2004) Newton's Second Law of Motion After developing the understanding of balance and unbalanced forces and Net force, it easy to look at Newton's second law of motion which states that: Time rate of change of momentum of any object is directly proportion to the net force being applied on the body and it causes the body to move in the same direction. Or "The acceleration produced by particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body and in the direction of that force (Jones, 2007)". The force which is applied on the body will move the body in the direction in which the force is applied. If the amount of force applied is doubled, double will be the acceleration. This law encompasses the motion behaviour of all the bodies which are subjected to unbalance forces. Firstly we need to understand how acceleration changes. Acceleration changes when the speed of an object changes or its direction changes. Now when forces are unbalanced they cause body to accelerate or decelerate. This change in acceleration is directly proportional to the net force applied and inversely proportional to the mass of object. The direction of movement is always in the direction of net force. If two or more forces are being applied on an object, the direction of movement under such case will be the direction of the net resultant of all the forces. Coming back to the definition which includes rate of change of momentum, momentum is defined as the product of mass and velocity. Conceptually it is simply the measure of how difficult is an object to stop. "The law defines a force to be equal to change in momentum per change of time (Benson, 2006)". The rate of change of momentum can be written as Force: Force = (m x v)/ (change in time) Since, acceleration is the rate of change of velocity, we can write: Force = m x (v/change in time) Force = m x a. Now we can understand the proportionality of acceleration with Force and Mass. Consider an object weighing 10 kg and is applied a force of 100 N. a = Force / mass If we double the force applied on the body, clearly the acceleration will be doubled. And if we double the mass of object, the acceleration will reduce to half. It is also easy to understand this proportionality with common day example. Suppose a car is out of fuel and a person tries to push the car alone. The car will move but very slowly. If another person comes to help in pushing, the same car will now move a bit faster. Similarly if a person is moving the car alone, it will be easy for him to push the car if it is empty rather than a situation when one or two person are sitting in the car. The unit of force is called Newton, named after Sir Isaac Newton. Force = m x a Force = kg x m/s2 1 Newton = kg- m/s2 It means if we want to move and object of 1 kg with an acceleration of 1 m/s2, we have to apply a force of 1 Newton. Newton's Third Law of Motion Newton presents the idea that whenever two objects come in contact with each other, they exert force on each other. "All forces occur in pair and these forces are equal in magnitude and opposite in direction (wikipedia, 2007)".This force results from the interaction of object. For example a book placed on a table is exerting a force equal to its weight on the table. In return the table is also exerting the same amount of force on the book, which is called the normal reaction. Newton's third law of motion can be stated as: For every action, there is an equal and opposite reaction. It means forces always come in pairs and for every action of force it has to encounter an equal opposite reaction F action = -F reaction The minus sign indicates that it is opposite in direction. Newton's law of motion does not have any mathematical formulation particularly of its own, but we can understand this law with the help of numerous common life examples. When a basket ball player hits the ground with his basket ball, the basket ball strikes the ground with the force applied by the player and tries to move the earth from its place (which obviously it can't due to the difference in their masses and huge inertia of earth surface), the earth in turn apply the same amount of force back on the basketball making it bounce back to player's hand. How we walk on ground When we walk on ground we exert a force with our foot on the ground and try to push it back. The earth in return exerts a same amount of force in opposite direction and pushes us forward, helping us to walk. Similarly the fish swims in water using the same phenomenon. It tries to push the water at the back of its fins. Water in turn applies the same magnitude of force in opposite direction which pushes the fish forward. Same case happens when we play tug of war. When we try to pull the rope towards us with our hands, the rope also tries to pull us towards it self and we feel like going forward. To counter this we exert a force on ground with our feet, the ground, according to third law of motion, also exerts the same force amount of force on us with opposite direction and this force eventually helps us to resist against the force exerted by rope. The three laws presented by Newton were very a great foundation upon which many further studies built their bases and a lot of further researched was carried out with the help of these laws. They are considered as one of greatest contribution done by any scientist to physics, science, human beings and to the development of this world. Bibliography Benson, (2006). Newton's Law of Motion. Retrieved on February 27, 2007: http://www.grc.nasa.gov/WWW/K-12/airplane/newton.html Henderson T. (2004).. Newton's First Law of Motion. Retrieved on February 28, 2007: http://www.glenbrook.k12.il.us/gbssci/phys/Class/newtlaws/u2l1a.html Jones, (2007). Newton's Second Law of Motion. Retrieved on February 27, 2007: http://physics.about.com/od/classicalmechanics/a/lawsofmotion_3.htm Wikipedia (2007). Newton's Laws of Motion. Retrieved on February 27, 2007: http://en.wikipedia.org/wiki/Newton's_laws_of_motion Read More