types of energy and the law of conservation of energy p. 236-241
Post on 01-Jan-2016
217 Views
Preview:
TRANSCRIPT
5.3
Types of Energy and the law of conservation of energy
p. 236-241
Energy Transformationssee p.236 chart
Any form of energy can be transferred from one place to another, or transformed from one form to another.
Whenever anything happens, energy is transferred or transformed.
Energy cannot be created or destroyed, and therefore, the total amount of energy in the system remains the same.
Section 5.3
Discussion: Forms and Types of Energy
Can you think of types of energy that each image represents?
Section 5.3
Forms and Types of Energy
electrical energy gravitational energy
elastic energysound energy
thermal energy
The law of conservation of energy states that energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.
9.7 Conservation of Energy
Efficiency of Energy Transformations
chemical → kinetic radiant → chemical
electrical → thermal chemical → kinetic
Conservation of Energy A system is a set of elements
that influence one another and on which external influences act.
Systems can be large (the universe) or small (an ant), and may contain many elements or as few as two.
When the energy interactions of a group of objects need to be analyzed, we often assume that these objects are isolated from all other objects in the universe.
Such a group is called an isolated system.
In an isolated system, the total amount of energy never changes.
Potential energy will become the kinetic energy of the arrow.
Conservation of Energy
As you draw back the arrow in a bow, you do work stretching the bow.
• The bow then has potential energy.
• When released, the arrow has kinetic energy equal to this potential energy.
• It delivers this energy to its target.
Conservation of Energy
Part of the PE of the wound spring changes into KE. The remaining PE goes into heating the machinery and the surroundings due to friction. No energy is lost.
Conservation of Energy
When the woman leaps from the burning building, the sum of her PE and KE remains constant at each successive position all the way down to the ground.
Conservation of Energy
The water behind a dam has potential energy that is used to power a generating plant below the dam.
• The generating plant transforms the energy of falling water into electrical energy.
• Electrical energy travels through wires to homes where it is used for lighting, heating, cooking, and operating electric toothbrushes.
Conservation of Energy
Mechanical Energy Mechanical energy (Em) is the sum of the
kinetic energy, and the potential energy of a system:
Quantifying Energy TransformationsPhase 1: Before the dive p.238 Since motionless diver kinetic energy is zero Ek=1/2mv2
Gravitational potential energy is Eg=mgh (calculate…)
Total mechanical energy: Em=Ek+Ep (calculate…)
Phase 2: At half way point
Once diver leaves platform he will accelerate down at 9.8m/s2; half way the diver is 5m above water
Eg=mgh Ek=1/2mv2 Em=Ek+Ep
To find V: v2=vi2 +2a d (calculate)
Now sub into Ek=1/2mv2
Phase 3: At the water’s surface Eg=mgh Ek=1/2mv2 Em=Ek+Ep
When diver reaches after his height above water is 0m, so Eg=0 (calculate to show this)
Ek=1/2mv2 to find v: v2=vi2 +2a d (calculate)
Sample problem A toy-car track is set up on a tabletop as shown
below. The mass of the car is 25 g. Calculate the speed of the car at the bottom of
the ramp, assuming friction is negligible.
Homework
P. 241 practice #1 P. 241 questions #1-4
p. 241 question #3
top related