Do I always have to draw the object as a dot?

Usually, yes. Treating the object as a single particle works perfectly for standard motion problems. You only need to draw the actual shape of the object if you are dealing with torque or rotation, where the exact point a force is applied matters.

What if I don't know the exact size of the forces yet?

Just estimate the lengths of the arrows based on what you do know. If the object is at rest or moving at a constant speed, the arrows in opposite directions should look roughly equal in length to show that they balance out.

Should I include velocity or acceleration arrows?

No, never put velocity or acceleration arrows directly on the dot with your forces. If you want to note the acceleration direction to help with your math, draw it off to the side so you don't accidentally mistake it for a force.

How do you draw a free-body diagram?

To draw a free-body diagram (FBD), you isolate the object you are studying by representing it as a simple dot or box, and then draw arrows pointing away from that dot for every external force acting on it. Think of it like drawing a map for a tug-of-war. Instead of drawing the people, the rope, and the muddy ground, you just draw a dot for the center of the rope and arrows for the pulling forces. This strips away all the visual distractions so you can cleanly apply Newton's laws of motion.

What goes into a free-body diagram?

A free-body diagram strips away the physical environment. The object itself becomes a single particle (usually a dot). The forces acting on that object become vectors (arrows). The direction of each arrow shows which way the force is pushing or pulling, and the length of the arrow roughly represents the strength (magnitude) of the force. Finally, every arrow must have a clear label, like $F_g$ for gravity or $F_N$ for the normal force.

Step-by-step drawing guide

First, define the object you are analyzing and draw a dot to represent it. Second, identify all the external interactions. Does gravity pull it down? Is a surface pushing up on it? Is a string pulling it? Third, draw an arrow for each of these forces, starting from the dot and pointing outward. Finally, define a coordinate system (an $x$ and $y$ axis) next to your diagram so you can break angled forces into components later.

Where students often slip up

The most common mistake is drawing forces that the object exerts on other things. A free-body diagram must only include forces acting on the object. Another frequent error is including a "net force" arrow. The net force is the mathematical result of adding all your arrows together; it is not a physical force itself, so it never belongs in the diagram.

Worked through

A 5 kg block sits at rest on a rough ramp angled at $30^\circ$ above the horizontal. Describe the free-body diagram and set up the equations of motion.

Step 1: Draw a dot for the block. Step 2: Draw the force of gravity ( $F_g = mg$ ) pointing straight down toward the bottom of the page. Step 3: Draw the normal force ( $F_N$ ) pointing perpendicular to the ramp's surface. Step 4: Draw static friction ( $f_s$ ) pointing up the ramp, parallel to the surface, to prevent the block from sliding down. Step 5: Choose a tilted coordinate system where the $x$ -axis is parallel to the ramp and the $y$ -axis is perpendicular. Breaking gravity into components gives $\sum F_x = f_s - mg \sin(30^\circ) = 0$ and $\sum F_y = F_N - mg \cos(30^\circ) = 0$ .

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Where this comes from: OpenStax University Physics Volume 1, Chapter 5 · Khan Academy: Forces and Newton's laws of motion