We already calculated the work done by the person as forty-seven joules. Let’s say the introduced kinetic friction force is a constant, nine-newton force. This gives us the concept of negative work, which can be illustrated by adding friction to our previous box-pushing scenario. When Θ is between 90° and 180°, cosΘ is less than zero which in turn makes work less than zero.Thus, when a force is applied to an object in a direction that is perpendicular to the object’s displacement, that force does no work. This happens when the force and displacement are perpendicular to each other. When Θ equals 90°, cosΘ equals zero which in turn makes work zero.This happens when the force and displacement are in the same direction, and thus we have our original formula, W=Fd. The addition of cosΘ to our formula brings some interesting concepts to light: Where F and d are the magnitudes of the force and displacement vectors, respectively, and Θ is the angle between the two vectors.) (For those of you familiar with vector calculus, we can represent work as the dot product of the force vector F and the displacement vector d: Now that the person is hunched over and exerting his force at an angle to the displacement, he is doing less work on the box: We can incorporate that into our earlier equation for work, giving: Only the horizontal component of the force vector, F cosΘ, is responsible for the work done on the box. In this case, not all of the force contributes to moving the box. If the person pushes with a constant, ten-newton force, and the box moves a distance of five meters in the direction the person has pushed, then the person has done fifty joules of work on the box:īut what happens if the direction the person pushes isn’t parallel to the direction the box moves? Let’s say the box isn’t very high, and the person has to hunch over to push it, causing the direction of his push to be directed at an angle of twenty degrees below the horizontal: The standard SI unit of work is the joule (J), which is equal to the work done by a one-newton force in moving an object one meter: Where W is work, F is force, and d is displacement. We can calculate exactly how much work was done by using the following formula: For example, if a person pushes on a box, and that box moves some distance, the person has done work on the box. Work is a physical quantity that is defined in terms of a force causing a displacement of an object. The Periodic Chart of Table of the Elements.Explanation of States of Matter Problems.SN1SN2 – Nucleophilic Substitution Reactions.Explanation of Numbers and Math Problems – Set 3.Explanation of Numbers and Math Problems – Set 2.Explanation of Numbers and Math Problems – Set 1.Metric Prefixes and Their Origins and Use.Drawing Cyclohexane Rings – Organic Chemistry.Alkanes and Alkenes – Organic Chemistry.Light & Dark Reactions in Photosynthesis.Search Lessons Search for: Science Resources and Science Lessons – Science Help
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