Chapter 7: Energy (From Lecture Slide) Flashcards
Energy
A property that can be used to determine how an object can change its state of motion or its physical shape
Energy existed in
Potential, kinetic, thermal, electrical, chemical, nuclear, or other various forms
All forms of energy are associated with
Motion
Principle conservation of energy
Energy can be neither created nor destroyed but only changed from one form to another
Energy is the property of a system that enables it to do
Work
Energy observed when it is
Being transferred or being transformed
Energy any given body has kinetic energy if it is in
Motion
A bow or spring has the potential for creating
Motion; it contains potential energy
Nuclear energy is
Potential energy becuase it results from the configuration of subatomic particles in the nucleus of an atom
Energy (Definition) is the
Property of a system that can be used to do work or to heat
Energy can be transferred but
Total amount in the universe does not change
Work
How long the force acts over a distance
Matter is
Substance we can see, smell, and feel and has mass and occupies space
Impulse
How long the force acts over time interval
A transfer of energy over a distance by
Some applied external force
Work are include three mains part of the conceptually
1) Involves force and distance
2) Is force times distance
3) In equation form: W = Fd
Two things occur whenever work is done:
1) A force acts on an object
2) The object subject to the force
If you push against a stationary brick wall for several minutes, you do not work
You may do work on your muscles, which stretch and contract, but not on the wall because the wall does not move
Twice as much work is
Done in lifting two loads 1 story high versus lifting 1 load the same vertical distance
Why twice as much work is?
Force needed to lift twice, the load is twice as much
Is there work being done in lifiting the barbell?
There is a force required to lift the weight of the barbell off the ground to a distance above the weightlifter’s head.
Work is done in lifiting a barbell. How much work is done in lifting a barbell that is twice as heavy the same distance?
This is in accord with work equals to the force x distance. Twice the force for the same distance means twice the work done on the barbell
You do work when pushing a cart with a constant force. If you push the cart twice as far, then the work you do is
Twice as much
A job can be done slowly or quickly. These methods require the same amount of work, but different amounts of
Power is the rate of which work is done, so doing the job faster requires more power
Mechanical energy is
In each something has been acquired that these object to do enables work
Mechanical energy is
Due to position or to or both these motions
There are two form of mechanical energy are
1) Potential
2) Kinetic
Potential energy: an object has by means of position
Stored energy held in readiness with a potential
Gravitaitional potential energy
Work is required to elevated objects against Earth’s gravity
The potential energy due to
Elevated
Whenever work is done to
Lift and energy is exchanged
The amount of gravitational potential energy possessed by an elevated object is
Equal to the work done against gravity in lifting it
The height is the distance above some chosen
A reference level such as the ground or the floor of a building.
Does a crate lifted by a pulley have increased potential energy relative to the floor?
If the crate were twice as heavy, its increase in potential energy would be twice as great
Does a car hoisted for repairs in a service station have increased potential energy relative to the floor?
Yes, if the car were twice as heavy, its increase in potential energy would be twice as great
What happen if the ball rolls down the end of the ramp?
Potential energy changes into kinetic energy
If an object is moving, it is capable of doing work
Depends on mass and speed
If an object’s speed is doubled, its kinetic energy is
Quadruptle
Does a car with momentum have kinetic energy?
Yes, because the car is in motion - Anything in motion necessarily has kinetic energy, regardless of whether it is accelerating or not
Net work is based on
The net force applied to the object and net force is combined with applied force and friction force
The net work equals the change in
Kinetic energy
Any change in kinetic energy is the restoring
Thermal energy
Only part of the total work that you do changes the object’s
Kinetic energy
The rest is changed by friction into
Thermal energy
How does energy transform?
Energy can change one form to another, and one location to another: heat and electromagnetic
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 work
Comparing kinetic energy and momentum (similarities)
Similarities between momentum and kinetic energy are both are properties of moving things
Comparing kinetic energy and momentum (differences)
1) Momentum is a vector quantity and therefore is directional and can be canceled
2) Kinetic energy is a scalar quantity and can never be canceled
An object moving with twice the velocity of another with the same mass, has
Twice the momentum but four times the kinetic energy
Machine device for
Multiplying forces or changing the direction of forces
Principle of underlying of every machine is
Conservation of energy
Machine cannot create energy but can transform energy
From one form to another or transfer energy from one location to another
Example of simple machines are
1) Lever
2) Pulley
Lever rotates on a point of support called
The fulcrum
Lever arms allows a small force over a large distance to
Induce a large force over a short distance
We do work on one end of the lever and the other end
Does work on the load
Fulcrum and point of support
It is closer to load (weight), small force over larger distance equal to larger force over a smaller distance
Pulley operates like a lever with
Equal arms, changes the direction of the input force
Lever and pullies are
Ideal system and operate at 100% efficiency (100% of work input = 100% of work ouput)
Energy is lost (dissipiated) through
Molecular kinetic energy and thermal energy
The lower the effficiency of a machine,
The greater the percentage of energy is lost to thermal energy
Efficiency
Percentage of work put into a machine that is converted into useful work output
Source of Energy: Concentrated energy
1) Nuclear Power
2) Stored in uranium and plutonium
3) By product is geothermal energy
4) Held in underground reservoirs of hot water to provide steam that can drive turbogenerators
