Energy & Its Impact on Global Society Jerome K. Williams, Ph.D. Saint Leo University Dept. Mathematics & Sciences

Chapter 2: Energy Mechanics Critical Thinking in Science Forms of Energy Primary Energy Souces & Energy Conversions Motion

Critical Thinking in Science Scientists seek to understand the physical world and how it works Making Observations Formulating Hypothesis Testing Hypothesis by Experimentation

Critical Thinking in Science A tentative statement that tries to generalize a series of observations is a hypothesis. A hypothesis that has been supported by a large number of observations and experiments is called a theory.

Forms of Energy Mechanical Energy Two Kinds Kinetic Energy (KE) – energy of motion Potential Energy (PE) –energy of position

Forms of Energy

Forms of Energy Chemical Energy – use fossil fuels & food for energy Nuclear Energy- energy found in atomic nucleus Thermal Energy: transfer heat between objects Electrical Energy – energy produced at power plants or stored in batteries Light (Radiant) Energy – also called electromagnetic radiation (ER); this covers a wide range of sources from radio and TV waves to X-rays and solar energy

Primary Energy Sources & Energy Conversions Chemical Nuclear Radiant Energy Conversion Processes are how primary energy sources are converted to an end use (powering a car, heating a home, using a laptop computer, etc.)

Primary Energy Sources & Energy Conversions

Motion Speed = distance traveled per unit time Velocity = similar to speed except it must include direction of travel Acceleration = change in velocity per unit time

Motion

Motion Force = push or pull on an object by other objects in environment Newton’s 2nd Law of Motion = acceleration of an object is directly proportional to the net force acting on it and inversely proportional to the object’s mass

Motion Units for Speed: Units for Force: Examples m/s, km/h, ft/s, mph Units for Force: Examples Newton (N), Pound (lb) Conversion Factors: 1 lb = 4.45 N Table 2.4

Example Problem 2.1 A 2000 kg car is acted on by a force of 6000 N by its wheels. Also acting on the car is a force of friction of 800 N. What is the car’s acceleration? Answer: 2.6 m/s2

Example Problem 2.2 Brakes are applied to a 1900 kg car moving at 80 km/h. In a time of 4.0 seconds, its velocity decreases uniformly to 30 km/h. What is the net force acting on the car? Answer: 6650 N