Energy and Heat: Key Concepts and Conversions
Questions
Describe how energy can be converted from one form to another in a wind-up toy. Elastic potential energy stored in the wound-up spring is converted to kinetic energy as the spring unwinds and the toy moves.
What is the law of conservation of energy state? Energy cannot be created or destroyed.
As an object falls in free fall, what energy change is taking place? Gravitational potential energy is converted into kinetic energy as the object falls.
What did Einstein conclude about the relationship between energy and mass? Energy and mass are equivalent, and can be converted into one another.
Questions
In what direction does heat flow on its own spontaneously? Heat flows spontaneously from hot objects to cold objects.
How is the temperature of an object related to the average kinetic energy of its particles? Temperature is related to the average kinetic energy of the particles in an object due to their random motions through space.
Name two variables that affect the thermal energy of an object. Mass of the object, temperature
What causes thermal expansion of an object when it is heated? Particles of matter tend to move farther apart as temperature increases.
How do the temperature increases of different materials depend on their specific heats? The lower a material’s specific heat, the more its temperature increases when equal amounts of thermal energy are added to equal masses.
What principle explains how a calorimeter is used to measure the specific heat of a sample material? A calorimeter uses the principle that heat flows from a hotter object to a colder object until both reach the same temperature.
Why is it necessary to have regularly spaced gaps between sections of a concrete sidewalk? The gaps provide space for concrete slabs to expand into so they do not buckle.
An iron spoon and silver spoon have the same mass. Which becomes hotter when both are left in hot tea for one minute? Both spoons absorb the same energy and have the same mass. Because silver has a lower specific heat (0.235 J/g•°C) than iron (0.449 J/g•°C), the silver becomes hotter.
If it takes 80.0 joules to raise the temperature of a material by 10.0C, how much heat must be added to cause an additional increase of 20.0C? Doubling the temperature change doubles the energy required, so 160 joules must be added.
What type of energy change results when friction slows down an object? Friction causes the conversion of kinetic energy to thermal energy.
Describe the energy of a playground swing at its highest position. The swing has maximum gravitational potential energy and no kinetic energy at its highest position.
Why does a bouncing ball rise to a lower height with each bounce? What energy conversion is taking place? Friction within the ball, between the ball and the ground, and between the ball and the air converts kinetic energy into thermal energy. Each bounce has less kinetic energy.
To begin a dive, a diver jumps into the air and then lands on the diving board, causing it to bend. What type of energy conversions occur as the board springs back and propels the diver up into the air? energy. Each bounce has less kinetic energy. The elastic potential energy of the board is converted into both kinetic energy and gravitational potential energy (because the diver’s height increases while the diver is still in contact with the board).