The document discusses various topics relating to work, energy and their conservation. It defines different forms of energy including kinetic, potential, chemical and mass energy. It states that energy is conserved in closed systems and can change forms but not be created or destroyed. Examples are provided to demonstrate calculations of kinetic and potential energy.

1. Work & Energy "There is nothing new to be discovered in physics now, All that remains is more and more precise measurement.” -Lord Kelvin “ Time is nature’s way of making certain that everything doesn't happen all at once.” -Woody Allen

2. Forces are vectors You can consider perpendicular motion independently. F=ma means: F x (total) = ma x F y (total) = ma y or: F (total) = m a y x F y F x F

12. Kinetic Energy E = 1/2 mv 2 E = energy (Joules) m = mass (kilograms) v = speed (meters/sec.) Marion Jones Sprints to Victory in the 200 meter.

14. Gravitational Potential Energy: E = mgh h = height g = * 9.82 m/s 2 m = mass * On Earth

15. Example of Potential Energy Cheryl Haworth lifts 297.6 lbs a distance of 2 meters m = 297.6 lbs x 0.453 kg/lbs = 135 kg mg = 135 kg x 9.8 m/s 2 = 1.3  10 3 Newtons E=mgh = 1.3  10 3 N x 2 m= 2.6  10 3 Joules E= 2.6  10 3 Joules  (1 Cal/4186 J) E = 0.63 Calories !!

16. Another Kinetic Energy Example A ball with mass of 0.5 kg is dropped from a distance of 10 meters. What is its kinetic energy when it hits the floor? We know that the ball falls towards the Earth with a constant acceleration of 9.8 meters/sec 2 . Last class we showed that the velocity gained after traveling a distance d is given by The kinetic energy is then

20. Conservation of Energy m = 50.9 kg

21. Work and Energy Definition: Work is the energy added to an object through the action of forces over a distance . Newton x meters = Joules F x d = W Force x distance = Work

23. Power The rate of doing work or expending energy P = Energy/Time Rock climbers gain a lot of potential energy but do so slowly, at low power

28. Summary Energy exists in many forms, for example in motion, the separation of masses, the separation of charges, mass… We will work mainly with potential energy and kinetic energy in this class. In a closed system, energy is conserved. This principal allows us to predict motion with out dealing with vectors.

29. James Prescott Joule (1818-1889) Joule determined the mechanical equivalent of heat by measuring change in temperature produced by the friction of a paddlewheel attached to a falling weight in the 1840s. He made a series of measurements and found that, on average, a weight of 772 pounds falling through a distance of one foot would raise the temperature of one pound of water by 1° F. This corresponds to (772 ft lbs)(1.356 J/ft lb) = 59 453.6 Calories, or 1 cal = 4.15 Joules, in close agreement with the current accepted value of 1 calorie = 4.184 Joules. The son of a prosperous brewer in North England, Joule financed his experiments himself.