Unit 2: Work, Energy, and Power Flashcards
Define and state the equation for kinetic energy:
Definition: The energy an object possesses by virtue of its movement. Stored in for example a ball that has been kicked.
Formula: 1/2 (M x V^2)
When velocity is doubled total KE is quadrupled (coz 2 squared = 4 so you multiply by 4)
If mass doubles then total KE doubles
If an unbalanced force acts in the same energy as velocity it causes the object to accelerate (if it is in the opposite direction of velocity it causes deceleration), this causes a change in velocity, this causes a change in the KE of the object.
Define and state the equation for gravitational potential energy:
Definition: The energy an object has due to its height in a gravitational field. Stored in any object that is lifted upwards.
Equation: G x M x H
Where G = Gravitational field strength, M = Mass, and H = Height
Do note that the equation can be re-written as
W x H
Where W is the weight (since G x M = W)
It is a scalar quantity. It is measured in joules. Mass is measured in KG.
How do you calculate a change in Gravitational potential energy?
Hint: You just have to change one thing in the original equation for GPE
GPE = mgΔh
Define and state the equation for elastic potential energy
The energy of an object being stressed, bent or compressed, found under the area of a force extension graph. For example, just before an arrow is fired from a bow, the bow is stretched and bent, storing elastic energy.
Equation: F = K x E
Define internal energy
Sometimes called heat or thermal energy, internal energy is the energy stored in a system. It includes the energy needed to change the state of a substance, from solid to liquid or liquid to gas. When an object has increased internal energy, the particles are moving faster or are pulled apart, as happens when a liquid turns into a gas.
Define chemical potential energy
Stored in the bonds of chemical compounds and released in chemical reactions. Food is a form of chemical energy, as are coal, wood and batteries. It is a form of stored energy so it does nothing until released and converted.
Define electric potential energy
The energy needed to move a charge against an electric field
Note: Don’t confuse “electric potential energy” for “electric potential”. They are 2 different things. “electric potential energy” is the one you need to know about. You don’t need to about electric potential but if you want to: The work done to bring the unit positive charge from infinity to that point (e.g. capacitors)
Define nuclear energy
Stored in every atom and released during nuclear fission or nuclear fusion. We use nuclear energy in a nuclear power station to release energy from uranium or plutonium to produce electricity.
Define sound energy
Sound energy is the movement of energy through a substance – such as air or water – in the form of waves. It is produced when a force causes an object or substance to vibrate.
Define radiant energy
Energy that is transferred by electromagnetic radiation, such as light, X-rays, gamma rays, and thermal radiation, which may be described in terms of either discrete packets of energy, called photons, or continuous electromagnetic waves.
The important thing to remember is that light is a type of radiation.
What is the principle of the conservation of energy? What is the equation for this?
additional: What is another way you can write this equation?
Energy cannot be created or destroyed, only converted from one form to another.
1st equation: ΣE in = ΣE out
another way: K1 + U1 = K2 + U2
where K = kinetic energy, and U = potential energy
Why does this work?: Coz the total energy of a system should equal its kinetic energy plus its potential energy
What is a system?
An object or a group of objects
What is a closed system?
A closed system can exchange energy (e.g. in the form of heat or work) with its surroundings, but not matter.
The change in a closed system will be equal but opposite to that change in its surroundings. Because there are only two things in the universe: my flask, and everything that surrounds my flask. Hence there is no net change in energy to that system, total energy is constant, forms of energy can change.
What is a open system?
A system which can exchange both energy and matter with its surroundings
Not a part of IGCSE syllabus
What is a isolated system?
Cannot exchange, energy or matter with its surroundings
Fill in the blanks:
Energy is a _______ that must be ________ to an object in order to perform ________, or heat up that object
Property
transferred
Work
You should know how to do sankey diagrams
Total energy in ——–> useful energy out
|
|
Wasted energy
Note: Change the size of the arrows, e.g. if there is more wasted energy output then that arrow should be thicker than the useful energy output arrow.
What are the energy conversions in a book falling?
GPE —-> KE ——> Sound
Look at the 5th page of this: https://drive.google.com/drive/u/0/folders/1-aNExVOD2hhVn_X370N7BYRd1cIAtNW_
Also remember that at the top the book is all GPE. Midway through it is 1/2 KE and 1/2 GPE.
Just before it falls on the ground it is all KE. and once its on the ground it is just potential energy.
What are the energy conversions in a pendulum?
GPE ——-> KE and back
point A of pendulum swing: Leftmost height
point B of pendulum swing: Exact centre
point C of pendulum swing: Rightmost height
Point w highest GPE: A & C
Point w lowest KE: A & C
Point w highest KE: B
Point w lowest GPE: B
Look at the 5th page of this: https://drive.google.com/drive/u/0/folders/1-aNExVOD2hhVn_X370N7BYRd1cIAtNW_
What are the energy transformations in a spring?
GPE —–> KE ——-> Elastic potential
(and backwards)
Look at the 5th page of this: https://drive.google.com/drive/u/0/folders/1-aNExVOD2hhVn_X370N7BYRd1cIAtNW_
Stop: Due to friction - energy is transferred out of the system.
What unit is energy measured in
Joules
Define and state the equation for work:
Equation:
Work = force x displacement
or
W = Fd
Definition: work done = energy transferred, causing object to move coz of external force, at least part of which is applied in the direction of displacement
Work is not done when:
- Circular motion (coz no displacement)
- displacement of body is perpendicular to force applied
- Work unit: Joule
- Force unit: Newtons
- Displacement unit: Metres
Is energy a scalar or vector quantity?
Scalar
Define and state the equation for power:
Power = work/elapsed time
P = W/ΔT
Where, W = work measured in joules, and T = time measured in seconds, and P= Power measured in watts
Definition: The rate at which energy is transferred or the work done in a given unit of time
1 watt = 1 joule per 1 second
Define and state the equation for efficiency
efficiency = (useful energy output/ energy input) × 100%
OR
efficiency = (useful power output/ power input) × 100%
Definition: How good a device is at transferring energy input to useful energy output
It is impossible for a system to be 100% efficient:
- energy will be dissipated
- in the form of heat
Distinguish between renewable and nonrenewable sources of energy
Describe how electricity or other useful forms of
energy may be obtained from:
chemical energy stored in fuel
– water, including the energy stored in waves,
in tides, and in water behind hydroelectric
dams
- GPE of water → Kinetic energy → Electrical
energy (energy losses: part of the KE is
converted to heat)
– geothermal resources
– nuclear fission
– heat and light from the Sun (solar cells and
panels)
– wind energy
Give advantages and disadvantages of each
method in terms of renewability, cost, reliability,
scale and environmental impact
https://drive.google.com/drive/u/0/folders/1cueM2j0n9VCFuaM_ofWRa-zPNhwMMs7z
Understand that the Sun is the source of energy
for all our energy resources except __________
geothermal,
nuclear and tidal
Understand that the source of tidal energy is
mainly the _______
moon
Show an understanding that energy is released by ________ _________ in the sun
nuclear fusion
When you kick a soccer ball you _____ energy
transfer
Energy transfers In a loudspeaker:
Electric potential → Sound
State and explain which one (amplitude or frequency) you think changes the amount of energy that comes out of a speaker:
Frequency: the number of waves passing a point (or being created or received) every second. (Units = hertz)
Amplitude: Height of wave. Relates to the amount of energy it carries. As amplitude increases, the intensity of sound increases.
Energy transfers in a Handheld dynamo with a lamp:
Chemical (human) → Kinetic → Electrical → Light
Handheld dynamo with a CRO (oscilloscope): Kinetic → electrical → light
Energy transfers in a Airzooka
Elastic potential energy → Kinetic energy + sound
Energy transfers in Raising a weight (with a motor/generator):
When weight is being raised: Electrical → Kinetic + GPE
When weight is falling: Electrical + GPE → KE
Energy transfers in striking a match
Chemical energy → light + thermal energy (both transferred to surroundings)
Trolley energy transformations:
Energy of trolley when masses falling: more KE
Energy of masses as they fall: GPE → KE
Mass vs Total mass: e.g. trolley with mass at the end. You may be measuring the energy transformation of the system. In this the mass that would be used in the equations would be the total mass (mass of the trolly + mass of the weight) rather than the mass of one of the individual objects.
Rock swung by string in horizontal motion: What is the work done on the rock by the string?
Answer: 0, nothing. Rock is not moving in direction of force.
