Master the Art of Free Body Diagrams: Understanding Vectors and Scalars

In summary, your teacher is suggesting that you use the equation for force, which is written in vector form, to calculate the acceleration of an object.
  • #1
primarygun
233
0
When we do free body diagram, we usually consider the vector as scalar.
I think this is a very important point, but why my teacher didn't clarify a lot?
 
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  • #2
primarygun said:
When we do free body diagram, we usually consider the vector as scalar.
I think this is a very important point, but why my teacher didn't clarify a lot?
No, we don't.
What you might be thinking of, is that we often write the vector as a MAGNITUDE (a non-negative scalar quantity) multiplied with a DIRECTION (a unit vector)
The direction is, of course, "readily" seen from the diagram.
 
  • #3
primarygun said:
When we do free body diagram, we usually consider the vector as scalar.
When you do a free body diagram, you are isolating a particular object and showing all the forces acting on it. These forces are certainly vectors, usually depicted as arrows in the diagram. What makes you think you are treating them as scalars?
 
  • #4
Note: Forces in x-axis are 5N and -5N. Find the acceleration.
My teacher would suggest us to
F=ma
5N-5N=ma
Hence, a=0.
The equation is the same,though, he never tells us 5N+(-5N)
 
  • #5
Forces are vectors.Period.The laws of Newton must be written in vector form...ALWAYS.
In your example,what if one of the forces would act as to make an angle (different from 0 or pi) with the direction of the other force...?

Daniel.
 
  • #6
primarygun said:
Note: Forces in x-axis are 5N and -5N. Find the acceleration.
My teacher would suggest us to
F=ma
5N-5N=ma
Hence, a=0.
The equation is the same,though, he never tells us 5N+(-5N)

It would make things more explicit to write out all the steps like this:

[tex] \bold F_{net} = m \bold a [/tex]

[tex] {\bold F}_1 + {\bold F}_2 = m \bold a [/tex]

[tex] F_{1x} + F_{2x} = m a_x [/tex]

[tex] (+5N) + (-5N) = m a_x [/tex]

[tex] 5N - 5N = m a_x [/tex]

[tex] 0 = m a_x [/tex]

[tex] 0 = a_x [/tex]

And of course if the y-components of the forces are zero, then [tex]a_y[/tex] is zero also, so [tex] \bold a [/tex] (the vector) equals zero.

But nobody ever actually writes out all those steps, in practice. I might do it that way once, when teaching it, just to clarify things.
 
  • #7
The way the problem is actually posted,it says nothing about an accelereration (or simply a nonzero velocity) in the "y" direction,so even if you come up with the conclusion that a_{x}=0,you still wouldn't tell how that body's moving.

Daniel.
 

1. What is a free body diagram?

A free body diagram is a visual representation of the forces acting on an object, typically a particle or a rigid body. It is used in physics and engineering to analyze the forces and resulting motion of an object.

2. Why is it important to do a free body diagram?

A free body diagram allows us to break down complex systems into simpler components and understand the forces at play. This helps in solving problems related to motion, equilibrium, and stability of objects.

3. How do I draw a free body diagram?

To draw a free body diagram, first identify the object of interest and all the forces acting on it. Then, draw the object as a point or a simple shape and represent the forces as arrows pointing in the direction of the force. Make sure to label each force with its magnitude and direction.

4. What are the types of forces shown in a free body diagram?

The most common types of forces shown in a free body diagram are weight, normal force, tension, friction, and applied force. These forces can be either contact forces (resulting from direct contact with another object) or non-contact forces (such as gravity).

5. Can a free body diagram be used for non-rigid bodies?

Yes, a free body diagram can be used for both rigid and non-rigid bodies. For non-rigid bodies, the forces acting on each individual particle within the body are represented, instead of the entire body as a whole.

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