Basic ideas of motion

Hey there, don't worry, in the following series of posts I promise I will not use any kind of physics jargon so that you might get confused. Don't worry I will just discuss the fun and basic ideas behind the theories of physics which, if you follow, will make you love physics.

Now, lets ask ourselves what do we mean by motion. 

Well, Motion is the term given to movement of a body from one point in space to another point in space. i.e. when I move my notebook from one place in the table to another, its called motion.

Now lets ask another question, Why does motion occur?

Well, motion occurs when we apply a certain amount of force to a body in a particular direction. The motion hence takes place in the following direction of the force applied. Hence we can deduce form this that without a force acting on a body, there will be no motion. Hence we can say, the body will remain at rest until and unless there is a force acting on it.

Now that we have applied force, What should the direction of the motion be?

Well, the direction of motion will be on the direction of the force applied. Lets take a block of cement in outer space (because in outer space you don't have gravity) and try and push it. What we will observe is that the block (after a brief application of force) will move linearly in the direction of the force applied. This keeps on going because there is no force to oppose the motion in outer space.
But if you try that on earth, there are multiple forces at at time acting on a body which prohibit a similar kind of motion.

Now, lets try an experiment,

Take whatever object you have in hand right now and keep it on the nearest table. Now what I want you to do is to try and push it in any direction. What you have done right now is that you applied force to move the object. Hence as a result of your application of force the object moved in a particular direction.

Now ask yourself another question, did you feel a push in your hand too when you were pushing the object?

Well, if you truly pushed the object, you certainly did feel a push (like the object is saying "I DON'T WANT TO MOVE!!"). That push which you felt was the opposing force whose objective was to oppose motion. But if you were able to move the object, your force was greater than the opposing force and hence you were able to push and move the object.

Now lets say you increase the force you apply gradually. What do you observe? 

Well,lets first get some concepts ready, first of if a body is in constant motion with respect to time in a particular direction then the body is said to be in a constant velocity, a good example of velocity is when a body is traveling with a velocity of 2m/s. What we mean to say by this is that the body covers 2 meters every second in a particular direction. Now coming to my answer, if we increase the force applied gradually then the velocity would also increase gradually. Hence the velocity of the body would keep on increasing at a constant rate. This rate of increase in velocity is known as acceleration. A good example of acceleration would be 2m/s^2, which means initially, when one second has elapsed, the velocity of the body will be 2m/s. Then when 2 seconds have passed the velocity of the body will increase to 4m/s  and so on and so forth.

Newton observed all the above phenomenons and postulated the three laws which help us understand physics in a better manner. His laws are as follows:

1. A body tends to stay in its state of rest or uniform motion until and unless there is a force acting on it to change its state.
2. The acceleration of the body is directly proportional to, and in the same direction as, the net force acting on the body, and inversely proportional to its mass. Thus, F=ma, where F is the net force acting on the object, m is the mass of the object and 'a' is the acceleration of the object.
3. Every force applied has a certain amount of equal and opposite force.

Each body has a certain amount of opposing force i.e. each body resists motion until and unless this amount threshold is crossed by the applied force. This tendency of the body is known as the inertia of the body.
You can try this if you want,
Take two objects, one heavy and another light ( for e.g. try a heavy book and a light book). As we can see the heavier body has more mass hence it has higher inertia i.e. we will require more force to displace it compared to the lighter book.
Hence the heavier the body is, more will be its inertia. and vice-versa.