# sir, i am finding it very difficult to draw free body diagrams. pls help.

36 Points
11 years ago

dear vivek,

Before you start to draw fre body diagram clearly state identify your System(The body to which you want to draw FBD).

And then remove everything other than system and draw the figure.

Now identify the active forces on the body(Gravitational force,Externally applied loads)

In Free body diagram along with active forces you've to show the reactions exerted ON the body BY the external elements.

Though many a times direction of reactive force is confusing so follow the above statement(on-by).Eventhough you give an opposite direction it doesnt effect your final answer.

You must've known about some basic reaction forces like hinge reactions and fixed joint reaction.

As per 12th standard i've explained an example below.

Now suupose u are drawing FBD of block having mass 'm' and also assume that if is moving down with accelaration 'a'.

then as I stated, first select your system(here sytem is block).

Now active forces--> Here, only external force is  gravitational force

Reactive forces: The surface in which block is lying will exert a normal reaction force'N'.As the block is sliding down  with an accelaration 'a' have the frictional force between block and suface will oppose its motion . Hence frictional force 'f' is shown.

The inertia force will also come into play . because of accelaration  of body and always it acts opposite directionto accelaration and having magnitude= m*a

If U want FBD for any particular question feel free to post.You can also refer to any good physics book like H C verma

thanks and regards,

dilipreddy.