1. Alta Conceptual Physics Energy Chapter 8

2. Alta Conceptual Physics Energy Facts There are different types of energy Energy of all types is measured in Joules Law of Conservation of Energy – Energy can be neither created nor destroyed, merely changed from one form to another

3. Alta Conceptual Physics Types of Energy (Unit Overview) Mechanical Potential Energy Energy of Position Gravitational Elastic Kinetic Energy Energy of Motion If it moves it has kinetic energy Heat Energy Heat is a form of Energy Transfer Other Forms of Stored Energy Chemical Fuels - usually release energy by combustion Food – energy released by digestion Electrical Generated from other forms of energy

4. Alta Conceptual Physics Work The Physics definition of work requires a displacement, i.e. an object must be moved in order for work to be done! The Applied force which causes the displacement contributes to the work, i.e. in order to contribute to the work, the applied force must be parallel to the displacement.

5. Alta Conceptual Physics Work: A Mathematical Definition Work = (Force)(Displacement) Units of Work = (Newton)(Meter) 1 NewtonMeter = 1 Joule A Joule is a unit of Energy and it takes energy to do work and work done on an object is stored as Potential Energy!

6. Alta Conceptual Physics Sample Problem What work is done sliding a 200 Newton box across the room if the frictional force is 160 Newtons and the room is 5 meters wide? W = F f ΔX = (160 N)(5 m) 800 Joules

7. Alta Conceptual Physics Power Power = Work/time = Joules/Second Mathematically there are two formulas for Power:

8. Alta Conceptual Physics Sample Problem What power is developed by a 55 kg person who does 20 chin ups, h = 3 m, in 45 seconds? P= w/t = FΔd/t = mgh/t (20(55 kg)(9.8 m/s 2 )(3 m))/45 sec = 718.6 Watts

9. Alta Conceptual Physics Energy of Position: Gravitational Potential Energy Occurs due to the accelerating force of gravity Is determined by the position of the object in the gravitational field Mathematically determined by: E p = mgh where m is mass, g is the acceleration due to gravity and h is the height above a determined baseline.

10. Alta Conceptual Physics Sample Problem What is the potential energy of a 10 kg rock sitting on a cliff 30 meters high? The acceleration due to gravity is 9.8 m/s 2. E p = mgh = (10 kg)(9.8 m/s 2 )(30 m) 2940 Joules

11. Alta Conceptual Physics Kinetic Energy Kinetic Energy is energy of Motion Any moving object has kinetic energy Dependent on the mass of the object and its velocity. Mathematically expressed as: E k = ½ mv 2

12. Alta Conceptual Physics Sample Problem What is the kinetic energy of a car with a mass of 2000 kg moving at 30 m/s? E k = ½ mv 2 = (½)(2000 kg)(30 m/s) 2 = 900,000 Joules

13. Alta Conceptual Physics Machines Three types of Simple Machines Lever – Directions of input and output are opposite Pulley - Changes direction of an applied force and it multiplies force Incline Plane – sacrifices distance for force, i.e you use less force but must travel a greater distance Mechanical Advantage Machines provide a mechanical advantage, i.e. they increase the force that you can provide

14. Alta Conceptual Physics Efficiency Efficiency is a measure of how well work is done.

15. Alta Conceptual Physics Sample Problem A pulley is used to lift a 500 Newton piano a distance of 3 meters off the ground. If the person pulling on the rope exerts a force of 200 newtons through a distance of 12 meters what is the efficiency of the system? Efficiency = (FΔd) out /(FΔd) in = (500 N)(3 m)/ (200 N)(12 m)= =62.5%