Article: A free body diagram is a quick sketch of an object that illustrates all of the forces acting on it and the direction these forces are acting. Read through the problem and draw a simple sketch of the object in question and the arrows representing every force acting on that object. For example: Calculate the net force of an object weighing 20 N sitting on a table being pushed towards the right with 5 N of force, but staying still because of a friction force of 5 N. The standard is to set arrows pointing upward or to the right as positive and arrows pointing downward or to the left as negative. Remember, you can have multiple forces working in the same direction. Forces that oppose each other will always have opposite signs (one positive, one negative).  If you are working with multiple force diagrams, make sure you keep the directions consistent throughout. Label the magnitude of each force with a “+” or “-“ sign based on the direction of the arrow you’ve drawn on the force diagram. For example: The force of gravity is a downward force making it negative. The normal force is upward making it positive. The push force is to the right making it positive, while the friction force acts to oppose this force towards the left (negative). Be sure to label all of the forces that are acting on the object. When an object is resting on a surface there is a downward force of gravity (Fg) and an equal force in the opposite direction called the normal force (Fn). In addition to these two forces, label the rest of the forces stated in the problem. Write the magnitude of each force in Newtons next to the given label.  A standard way to label forces is with a capital F and a subscript of first letter of the force. For example, if there is a force due to friction, label it Ff. Force due to gravity: Fg = -20 N Normal force: Fn = +20 N Friction force: Ff = -5 N Push force: Fp = +5 N Now that you have labelled all forces with both a direction and magnitude, you just need to add all of them together. Write an equation for net force (Fnet) where Fnet is equal to the sum of all the forces acting on the object. For example: Fnet = Fg + Fn + Ff + Fp = -20 + 20 -5 + 5 = 0 N. Because the net force is 0 N, the object is stationary.
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Draw a free body diagram. Establish the positive and negative directions of forces. Label all forces. Sum the magnitudes of all the forces.