Physics Unit 2: Energy, Work, Power, and Thermal Physics

Vocabulary flashcards covering core definitions, formulas, concepts, risks, and sample calculations from Physics Unit 2 lecture notes and study guides.

Kinetic Energy

The energy an object possesses because of its motion; simply defined as the energy of motion, calculated using the formula $E_k = \frac{1}{2} m v^2$.

Potential Energy

The energy an object has because of its position or location, such as energy of position due to gravity.

Work

The product of the magnitude of force and the parallel distance through which an object moves ($W = F \times D$); the process of energy transfer.

Power

The time rate of doing work, calculated mathematically as $P = \frac{W}{t}$.

Joule

The SI unit used to measure energy and work.

Energy

The ability to do work; an object that has energy can do work.

Gravitational Energy

The stored energy that comes from doing work against gravity, which is equal to the work done.

Conservation of Total Energy

The principle stating that the total energy of an isolated system remains constant, as energy cannot be created or destroyed.

Kilowatt-hour

A unit of energy equal to power multiplied by time ($E = P t$).

Alternative Energy Sources

Energy production methods that replace traditional fossil fuels (coal, oil, gas), such as solar panels, wind energy, and nuclear power.

Renewable Energy Sources

Natural energy sources that naturally replenish over time, such as solar, wind, and hydropower.

Non-renewable Energy Sources

Energy sources that do not replenish, including coal, oil, natural gas, and uranium.

Positive Work

Work done when the applied force and the displacement of the object are in the same direction, adding energy to the system.

Negative Work

Work done when force and displacement act in opposite directions, causing energy to leave the system and decrease system energy.

Zero Work

A condition in which no work is performed because there is zero displacement ($D = 0$), such as pushing against a stationary wall.

Closed System

A physical system in which the total energy is always constant because energy is conserved and no energy enters or exits.

Energy Transformation of a Falling Object

As an object falls, potential energy decreases because height decreases, kinetic energy increases because speed increases, and total energy remains constant due to energy conservation.

Energy Transformation of a Thrown Object

As an object travels upward, kinetic energy decreases while potential energy increases; as it falls back down, potential energy converts back into kinetic energy, returning the object to its initial speed just before impact (neglecting air resistance).

Chemical Energy Risks

Environmental risks associated with chemical energy sources, including pollution and the emission of harmful gases.

Nuclear Energy Risks

Hazards associated with nuclear energy, including radioactive waste management and the risk of severe accidents.

Radiant Energy Risks

Limitations of radiant solar energy, which depends on sunlight and produces less energy when light levels are low.

Dependence on Oil

Society's historic dependence on oil because burning oil easily produces large amounts of energy used for light, heat, transportation, and air conditioning.

Effect of Doubling Speed on Work

Doubling the speed of a moving object requires four times ($4 \times$) more work to bring it to rest because speed is squared in the kinetic energy formula ($E_k = \frac{1}{2} m v^2$).

Bank - Energy Diagram

A conceptual model that uses financial terms (bank, checking, savings) to illustrate energy conservation, where heat input and work on the system act as positive energy transfers ($+$), while heat output and work done by the system act as negative energy transfers ($-$.

Temperature

A measure related to the average kinetic energy of the particles within a material or system.

Heat

Thermal energy transferred from one body or system to another due to a temperature difference.

Specific Heat

The amount of heat required to raise the temperature of a unit mass of a substance by one degree.

Latent Heat

The energy absorbed or released by a substance during a change of phase at a constant temperature.

Conduction

Heat transfer occurring through direct molecular contact within or between materials.

Convection

Heat transfer in a fluid (liquid or gas) caused by fluid motion and density variations that establish convection currents.

Radiation

Heat transfer occurring via electromagnetic waves through space without requiring a physical medium.

Graph of Heat Added versus Temperature

A plot depicting state and phase changes as heat is added at a constant rate, where sloped lines indicate heating within a single phase (solid, liquid, or gas) and flat plateaus indicate phase transitions occurring at constant temperature (points A-B for melting and C-D for boiling).

Stairway Climbing Work and Power Calculation

For a student weighing $568\text{ N}$ who climbs a vertical height of $3.2\text{ m}$ in $24\text{ s}$, the work done is $W = 568 \times 3.2 = 1817.6\text{ J}$ and the power output is $P = \frac{1817.6}{24} = 75.73\text{ W}$.

Microwave Oven Electrical Energy and Cost Calculation

For a microwave oven requiring $1242\text{ W}$ running for $4.4\text{ min}$ ($0.07333\text{ h}$), the energy used is $1.242 \times 0.07333 = 0.09108\text{ kWh}$, costing $0.09108 \times 13 = 1.18404\text{¢}$ at a rate of $13\text{¢}$ per kWh.