Work Work – when a force causes an object to move in the direction of that force. Work & Energy are scalar quantities. Joule (J) – SI unit for Work & Energy James Prescott Joule (1818-1889) – English physicist; studied heat and work. This led to the theory of conservation of energy. Developed Kelvin scale with Lord Kelvin.
Work Done by a Constant Force Equation: As long as this person does not lift or lower the bag of groceries, he is doing no work on it. The force he exerts has no component in the direction of motion.
Work Done by a Constant Force Work done by forces that oppose the direction of motion, such as friction, will be negative.
6-2 Work Done by a Varying Force (For those who know calculus)For a force that varies, the work can be approximated by dividing the distance up into small pieces, finding the work done during each, and adding them up. As the pieces become very narrow, the work done is the area under the force vs. distance curve.
Conservation of Energy Just like conservation of mass and conservation of momentum, this means that the total energy of the system is constant. Energy gets rearranged into different forms, but the total amount stays the same.
How is energy rearranged? Think of a roller coaster. – There is work done to lift you up the first hill – At the top of that hill you have potential energy – You roll down the hill and gain kinetic energy as you lose potential energy – As you roll up the next hill, you trade the kinetic energy you gained to build back potential energy