A 1 kg brick sits on a shelf. It is not moving. It is not falling. It just sits there. Locked inside that ordinary brick is more energy than the brick could ever gain by moving or by being lifted.
You can already name the familiar forms of energy: kinetic energy for a moving object, gravitational potential energy for a lifted object, thermal energy for a hot one. This lesson adds one more form. Every object carries far more of it than of any other form.
An object's mass measures an amount of energy locked up in the object.
The 1 kg brick on the shelf has no kinetic energy and only a little gravitational potential energy.
On top of those, the brick carries energy in its mass itself.
The brick does not need to move, warm up, or sit high for this energy; its mass alone measures it.
The same holds for every object: a parked truck, a cold stone, and a sheet of paper each carry energy in their mass.
More mass means more of this locked-up energy.
How much energy does a given mass hold? The next lessons put a number to the exchange.
A granite boulder rests at the bottom of a valley, cold and still. Does the boulder carry energy in its mass?
Mass is itself a form of energy.
The boulder has mass, whether or not it moves, warms, or sits high.
So the boulder's mass measures an amount of energy locked up in it.
Yes. The boulder carries energy in its mass, on top of any other energy it has.
A hockey puck slides to a stop on rough ice. Its kinetic energy is gone. Does the energy locked in the puck's mass remain?
Friction took the puck's kinetic energy away.
The puck's mass is still there, and mass is itself a form of energy.
So the puck's mass still measures an amount of locked-up energy.
Yes. The puck lost its kinetic energy, but the energy in its mass remains.
A delivery truck sits parked and still in a lot. Which of the following does the truck's mass measure?
Delphine says: 'A book lying still on a table carries energy locked up in its mass.' Is Delphine correct?
Which form of energy does every object carry, whether it is moving or still, stretched or relaxed?
A sack of flour sits on a pantry floor: not moving, not lifted, settled at the room's temperature. Which statement about the sack is true?
Mireille lifts a stone from the ground onto a high wall. What happens to the energy locked up in the stone's mass?
Which statement about mass and energy is true?