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MassachusettsPhysics

Module 4: Energy and work

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

If energy is never created or destroyed, how does it move between forms while the total stays the same?

State the law of conservation of energy, apply it to mechanical systems by setting the energy before equal to the energy after, and account for energy transformed into thermal energy (MA STE Introductory Physics, Energy, HS-PS3-1, HS-PS3-2).
A standard-level answer on conservation of energy for the Massachusetts High School Introductory Physics MCAS: energy is never created or destroyed, only transformed, and how to apply the before-equals-after method to mechanical systems, including energy lost to friction as thermal energy.
13 min answer →

How do devices convert one form of energy into another, and why is no device ever perfectly efficient?

Describe how devices convert energy from one form into another, define efficiency as useful output over total input, and explain why some energy is always transformed into unwanted thermal energy (MA STE Introductory Physics, Energy, HS-PS3-3).
A standard-level answer on energy conversion devices for the Massachusetts High School Introductory Physics MCAS (HS-PS3-3): how devices convert energy between forms, efficiency as useful output over total input, and why some energy is always lost as unwanted thermal energy.
12 min answer →

How is energy stored when two objects interact through a gravitational, electric, or magnetic field, and how does it change as they move?

Model two objects interacting through a gravitational, electric, or magnetic field, and describe how the energy stored in the field changes as the objects move closer or farther apart (MA STE Introductory Physics, Energy, HS-PS3-5).
A standard-level answer on energy stored in fields for the Massachusetts High School Introductory Physics MCAS (HS-PS3-5): how two objects interacting through gravitational, electric, or magnetic fields store energy, and how that stored energy changes as they move closer or farther apart.
12 min answer →

How is energy stored in a moving object and in an object's position, and how do you calculate each?

Define kinetic energy as the energy of motion (KE = 1/2 mv^2) and gravitational potential energy as the energy of position (PE = mgh), and calculate each (MA STE Introductory Physics, Energy, HS-PS3-1, HS-PS3-2).
A standard-level answer on kinetic and potential energy for the Massachusetts High School Introductory Physics MCAS: kinetic energy as the energy of motion (KE = 1/2 mv^2), gravitational potential energy as the energy of position (PE = mgh), and how to calculate both.
12 min answer →

What is thermal energy, why does heat always flow from hot to cold, and how do we calculate the heat needed to change a temperature?

Describe thermal energy as the energy of particle motion, state that heat flows spontaneously from hotter to colder regions (the second law), and calculate heat using Q = mc(delta-T) (MA STE Introductory Physics, Energy, HS-PS3-2, HS-PS3-4).
A standard-level answer on thermal energy and heat transfer for the Massachusetts High School Introductory Physics MCAS: thermal energy as the energy of particle motion, the second law (heat flows from hot to cold), the three modes of heat transfer, and the specific heat calculation Q = mc(delta-T).
13 min answer →

When does a force do work, how much energy does it transfer, and how fast is that energy transferred?

Define work as a force acting through a distance (W = Fd), define power as the rate of doing work (P = W/t), and apply both to everyday situations (MA STE Introductory Physics, Energy, HS-PS3-1).
A standard-level answer on work and power for the Massachusetts High School Introductory Physics MCAS: work as a force times distance (W = Fd), power as the rate of transferring energy (P = W/t), and their units, the joule and the watt.
12 min answer →