Which of the following is the best example of potential energy?
question 1 options:
a ball sitting at the top of a hill
a ball sitting at the bottom of a hill
a ball rolling down a hill
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question 2 (1 point) question 2 unsaved
which of the following is an example of kinetic energy?
question 2 options:
a girl running in a race
a car sitting motionless
a tank containing gasoline
a sled sitting at the top of a hill
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question 3 (1 point) question 3 unsaved
the water held by a dam is an example of which type of energy?
question 3 options:
kinetic energy
chemical energy
electrical energy
potential energy
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question 4 (1 point) question 4 unsaved
what does the kinetic theory explain?
question 4 options:
heat is due to pascal´s principle.
heat is due to temperature.
heat is due to potential energy.
heat is due to the motion of molecules.
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question 5 (1 point) question 5 unsaved
if the atoms and molecules of a substance are moving very fast, the substance is
question 5 options:
porous
cold
hot
frozen
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question 6 (1 point) question 6 unsaved
heat energy is measured indirectly by
question 6 options:
temperature
kinetics
recording the motion of molecules
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question 7 (1 point) question 7 unsaved
what are the ways that heat moves?
question 7 options:
heat only moves through air currents.
heat moves through conduction, convection, and radiation.
heat only moves through conduction and radiation.
heat moves from a cold object to a warm object.
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question 8 (1 point) question 8 unsaved
convection requires to transfer heat.
question 8 options:
the vacuum of space
fluids (liquids or gases)
insulation
solids
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question 9 (1 point) question 9 unsaved
what does an insulator do?
question 9 options:
an insulator slows heat transfer.
an insulator cools a substance.
an insulator warms a substance.
an insulator emits electromagnetic radiation.
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The best example of potential energy is a ball sitting at the top of a hill.

An example of kinetic energy is a girl running in a race.

The water held by a dam is an example of potential energy.

A kinetic theory explains that heat is due to the motion of molecules.

If the atoms and molecules of a substance are moving very fast, the substance is hot.

Heat energy is measured indirectly by temperature.

It should be noted that heat only moves through conduction and radiation.

Convection requires fluids (liquids or gases) to transfer heat.

The function of an insulator is that it slows heat transfer.

The main difference between potential and kinetic energy is that while the potential energy is stationary, kinetic energy is the energy in motion.

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1. a ball sitting at the top of a hill

Explanation: potential energy is the energy related to the position of an object: in particular, gravitational potential energy is the energy that an object possesses due to its height relative to the ground. It is given by

where m is the mass of the object, g the gravitational acceleration and h the heigth of the object above the ground. From the formula, we see that the higher the object above the ground, the larger h, so the greater the potential energy: among the choices given, the ball sitting at the top of the hill has therefore the largest potential energy.

2. a girl running in a race

Explanation: kinetic energy is the energy due to the motion of an object, and it is given by

where m is the mass of the object and v its speed. In this problem, we see that the only situation in which the object is moving is the first one (girl running in the race): in all other cases, the objects are at rest, so their speed is zero and their kinetic energy is zero as well.

3. potential energy

Explanation: as stated in #1, potential energy is the energy due to the height of an object relative to the ground. In this case, the water held by the dam has potential energy, because it is held at a certain height above the ground (this energy will be eventually converted into kinetic energy as the water is released and falls down)

4. Heat is due to the motion of molecules.

In the kinetic theory, gases consist of atoms/molecules that are continuously moving. One of the consequences of the kinetic theory is that the temperature of a gas is directly proportional to the average kinetic energy of its atoms/molecules: in a hotter gas, molecules move faster, while ina colder gas, molecules move slower.

5. hot

Explanation: as stated in the previous exercise, the temperature of a gas is directly proportional to the average kinetic energy of its molecules, which is proportional to the square of the speed of the molecules. This means that if the molecules move faster, the substance is hotter, while if the molecules move slower, the substance is colder.

6. temperature

Explanation: heat and temperature are strictly related but they are slightly different. In fact, heat is a measure of the total energy due to the motion of the molecules in a substance; on the contrary, temperature gives a measure of the average energy of motion of the molecules in the substance. The two quantities are of course strictly related, because when the average kinetic energy is higher (higher temperature), the total energy (heat) is alse greater.

7. Heat moves through conduction, convection, and radiation

Heat can move through 3 different methods:

- Conduction: this occurs when heat is transferred through the collision between the molecules of two different mediums (or two different parts of the same substance)

- Convection: this occurs in fluids, when an external heat source heats the molecules in a part of the fluid. This part of the fluid becomes less dense, so it rises and it replaces the colder part, which sinks. The mechanisms continues, generating the so-called convection current.

- Radiation: this occurs when heat is transferred by electromagnetic waves. This is the only method of heat transfer that can occur also through a vacuum.

8. fluids (liquids or gases)

Explanation: as stated in the previous exercise, convection is one of the three methods of heat transfer, and it occurs in fluids. Convection occurs when an external heat source heats the molecules in a part of the fluid. This part of the fluid becomes less dense, so it rises and it replaces the colder part, which sinks. The mechanisms continues, generating the so-called convection current. Convection cannot occur in solids because in solids molecules are not free to move.

9. An insulator slows heat transfer

Explanation: an insulator is a material which slows down the heat transfer. Air is an example of good insulator.

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