# Newtons Laws of Motion

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