How to Draw a Free Body Diagram in Physics

Draw free body diagrams to solve physics problems

Free body diagrams are an essential tool in solving classical physics problems. Here's how to draw free body diagrams in physics, set up the problem, and use other physics equations to get the answer you need.

Things You'll Need

• Basics physics knowledge
• Paper
• A writing utensil

Instructions

1. 

   Free body diagrams in physics usually deal with physics systems. You want to draw a free body diagram when you have a physics problems where forces are acting upon the given system. You generally have a specific variable or item you are trying to solve for. Isolate the object you are interested in. For example, if you have a block on a ramp and are interested in only the block, redraw the block separate of the ramp.

2. 

   Next, draw the forces that are acting upon the object. Recall that force is equal to mass times acceleration (F=m*a). If no external forces are acting upon the object, do not forget about gravity. In this example, mg represents the force of gravity, and N is the normal force of the ramp acting upon the block (remember Newton's 3rd Law which you should know from your basic physics knowledge). Also do not forget frictional forces, Fs (if you are doing problems with friction).

3. 

   Next, break up the forces into components. Use your trigonometry skills and remember how to use sines and cosines. Do not forget you can rearrange force locations, as long as they remain consistent.

4. Now you can use your kinematics equations to determine things like how long it will take for the block to slide down the ramp. As we can see from the pictures, we know that the friction force, Fs, is equal to mg*sin(Θ). We can also see that the normal force is equal to mg*cos(Θ).

5. Most physics problems will have the free body diagram as the initial part of the problem. After you find what variables or equations you need from the free body diagram, you can use your kinematics equations to solve for things like the amount of time it will take for the block to slide down the ramp. Now you can use physics free body diagrams to set up and solve physics problems!

Tips & Warnings

• Practice makes perfect when it comes to solving physics problems

• Whenever possible, try drawing pictures to help solve your problems

• If you need to, do not hesitate to get physics tutoring. Physics can be a very difficult subject until you master it, and having someone go through it with you can be very helpful.

• Make sure you keep your sign convention consistent.