Flashcards in Energy Deck (38):
Energy is a concept central to all of what?
a combination of what make up the universe?
matter and energy
abstract, can't be seen, smelled or felt
The idea of energy was unknown to who?
- existance was debated
persons, places and things have energy but we usually observe energy when it is
being transffered or transformed
if WORK is to be done what do things must occur
1) Application of force
2) Movement of something by that force
- Displacement must occur for work to occur
one joule of work is done when what happens?
a force of 1 newton is exerted over a distance of 1 metre
the rate at whitch work is being done on an object
Power is vector or scalar? What's its unit?
Scalar; Joules/Seconds = Watts (W)
One watt of power is expended when what happens?
1 joule of work is done in 1 second
typically engines/motors are rated in
horsepower and elctricity in watts
1 HP =?
750 Watts (W)
Energy can take many forms. Mechanical energy is a form of energy due to (2)
a) the relative position of interacting bodies - Potential Energy (PE)
b) due to their motion - kinetic energy
Unit for work and energy
Potential Energy (5)
- an object may store energy because of its postition relative to some other object
- in this stored state it has the potential to do work
- work is required to elevate objects against Earth's gravity - gravitation potential energy
- Gravitation potential energy = weight X height
PE = m(g) X h
Kinetic Energy (5)
- one of the kinds of energy into which PE can change into
- can be reffered to as energy of motion
- depends on an object's mass and speed
- can only be 0 or positive
KE = 1/2 m (v^2)
Work energy theorem
the work energy theorem states that the work done on a system (net work) equals the energy changes
W = Delta KE
= KE (final) - KE (initial)
= 1/2m (v^2) - 1/2m (v^2)
Law of Conservation of Energy
Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes
In a closed system the total amount of energy at the start is ___ as the total amount of energy at the end
Law of Conservation of Energy equation
KE (initial) + PE (initial) = KE (final) + PE (final)
KE (initial) + PE (initial)= KE (final) + PE (final) + heat
Machines are devices for what?
multiplying forces or simply changing the direction of forces
- every machine is the Conservation of Enery Concpet
2 examples of common machines
and how they change direction or multiply the force
- lever - pulley
- by giving up distance
Machine lever/pulley equation
(Force X Distance)input = (Force X Distance) output
- represents the percent of work put into a machine that is converted to useful work output
efficiency = (useful energy output) / (total energy input) X 100
What would happen in an idea machine?
What happens in reality?
Idea: 100% work input appears as work output
Reality: Doesnt happen because thermal energy is dissipated
What is the graveyard of kinetic energy
Sources of energy in the world
majority of the world's energy - fossil fuels
- then nuclear
then non-sustainable biomass
- the rest s a mixture of renewable (geothermal, solar, wind etc.)
List 5 sources of energy
any of the following
- fossil fuels, geothermal, nuclear fission, solar energy, wind energy, hydroelectric power
heat is a type of
Kinetic molecular theory (KMT) is based on what assumption?
the assumption that matter is made up of many tiny particles that are always in motion. In a hot body, the particles move faster, and thus have a higher energy than in a cooler body
Using the KMT we say temperature is
the average kinetic energy of particles in a material
Heat (Q) is
the energy that flows from a substance of hot temp. to a substance of cold temp
specific heat capacity (c)
the quantity of heat per unit of mass required to raise the temp by 1 degree celcius.
- every material has its own specific heat capacity
- it is a property of the material
Conservation of Energy and Equilibrium
- when two materials transfer heat to each other all the heat that one material gains comes from the heat the other material loses
- when two materials are in contact long enough they will eventually reach thermal equilibrium which means they will have the same temp
- heat will transfer from hot to cold until thermal equilibrium is reached
- a collision in which colliding objects rebound without lasting deformation or the generation of hear
- both momentum and kinetic energy are conserved