Presentation on theme: "What is energy?. Chain of energy Newton’s Laws 1.An object in motion will stay in motion (or rest at rest) unless acted on by an outside force. (Inertia)"— Presentation transcript:
What is energy?
Chain of energy
Newton’s Laws 1.An object in motion will stay in motion (or rest at rest) unless acted on by an outside force. (Inertia) 2.Force = mass x acceleration (Units: Newtons = kg x m/s 2 ) 3.For every action there is an equal and opposite reaction.
Work Energy = ability to do work Work = force exerted over a distance W (or “energy”) = F x d 1 Joule = 1 Newton x 1 meter 1 Joule = 1 Newton x 1 meter 4.18 Joule = 1.00 calorie 4.18 Joule = 1.00 calorie
Power Rate at which work is done Power = Work / time Watts = Joules / seconds SO… Energy can also be expressed this way: Energy = Power x time Joules = Watts x seconds
Consider: What does it mean to give electrical appliances a rating in watts? What is a kilowatt? What is a killowatt-hour? Why do we describe food in terms of calories?
Forms of Energy Kinetic energy = Energy of moving objects KE = ½ mass x velocity 2 KE = ½ mv 2 Joules = ½ kg x (m/s) 2 Potential energy = Energy stored due to position or composition PE = mass x acceleration due to gravity x height PE = mgh Joules = kg x m/s 2 x m
Consider: How do each of the following represent KE? Heat radiating from a car The sound of my voice Muscles contracting Light traveling to your eye
Consider: How do each of the following represent potential energy? A book on the edge of a table A slice of pizza Two magnets near each other An electrical outlet A stretched rubber band
What is heat? Kinetic energy caused by atoms moving and colliding Flows from warm body to cold body Not the same as temperature
Temperature Scales ° F = (1.8 x ° C) + 32 ° C = (° F – 32) / 1.8 Both use freezing and boiling points of water as standards Kelvin = ° C – K = absolute zero
Specific Heat Ability of a material to absorb/lose heat Q = mc Δ t Heat gained/lost = mass x specific heat x change in temp If two substances have equal mass and equal change in temp., what does the amount of heat gained depend on?
Heat transfer Conduction – transfer due to atoms colliding or vibrating Convection – transfer due to bulk movement of a fluid (gas or liquid) Radiation – transfer due to electromagnetic radiations (uses electrical/magnetic fields instead of matter) file:///Users/johnb/Desktop/lsps07_int_heattransfer/lsps07 _int_heattransfer.html file:///Users/johnb/Desktop/lsps07_int_heattransfer/lsps07 _int_heattransfer.html How can these types of transfer work together?
1 st Law of Thermodynamics: Conservation of Energy Energy cannot be created or destroyed but can be transformed PE = KE mgh = ½ mv 2 How can our examples of PE be converted into KE? Is the reverse also true? Are energy conversions 100% efficient?
2 nd Law of Thermodynamics: Entropy Statements: 1.Heat will not flow spontaneously from a cold to a hot body. 2.You cannot construct an engine that does nothing but convert heat to useful work. 3.Every isolated system becomes more disordered with time. (Entropy) t/diffusion.swf t/diffusion.swf
Applications Can any system transfer energy with 100% efficiency? What does this mean in living systems? How do we maintain order in systems (especially living systems)? Where does energy go? Is it truly “lost”?
Back to the Sun – Nuclear Fusion High pressure and high temperature force atoms together Mass converted to energy Energy radiates into space How do atoms relate to energy?