To calculate the normal force of an object at rest when an outside force acts upward on that object, use the equation: N = m * g - F * sin(x)'   N refers to the normal force, m refers to the object's mass, g refers to the acceleration of gravity, F refers to the outside force, and x refers to the angle between the object and the direction of the outside force.  Example: Find the normal force of a block with a mass of 4.2 kg, when a person is pulling up at the block at a 50 degree angle with a force of 20.9 N. The weight of an object equals the mass of the object multiplied by the acceleration of gravity.  Note that the gravitational acceleration at the Earth's surface is a constant: g = 9.8 m/s2   Example: weight = m * g = 4.2 * 9.8 = 41.16 The sine of an angle is calculated by dividing the side of the triangle opposite the angle by the hypotenuse of the angle.  Example: sin(50) = 0.77 The outside force refers to the force acting upward on the object, in this instance.  Example: 0.77 * 20.9 = 16.01 Doing so will give you the normal force at work.  Example: 41.16 – 16.01 = 25.15 Note that for an object at rest being influenced by an external, upward force, the normal force will be less then the weight of the object.  Example: The normal force is 25.15 N.
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