Unit 4 - Energy

Question 1

What is energy?

Answer 1

The capacity to do “work”.

Question 2

Define thermal energy

Answer 2

Thermal energy: atoms possess thermal energy – the faster they move the greater it is

Question 3

Define electrical energy

Answer 3

Electrical energy: possessed by charged particles, transferred as they move through a circuit

Question 4

Define radiant energy

Answer 4

Radiant: travels via waves, no particles required

Question 5

Define nuclear potential

Answer 5

Nuclear potential: the nucleus of every atom has stored energy which can be released via fissions, etc.

Question 6

Define gravitational potential

Answer 6

Gravitational potential: a raised object has stored energy due to its position above some reference level

Question 7

Define kinetic energy

Answer 7

Kinetic: every moving object has energy of motion – kinetic energy

Question 8

Define elastic potential

Answer 8

Elastic: potential energy stored in objects that are stretched or compressed

Question 9

Define sound energy

Answer 9

Sound: produced by vibration, travels by waves through a material to the receiver

Question 10

Define chemical potential

Answer 10

Chemical potential: in chemical reactions, new molecules are formed and energy is released or absorbed

Question 11

Explain work and its directions

Answer 11

When a force acts on an object and causes displacement, it is said that work is down.

Work is measured in Joules (J)

W = F x D (x cos0) – the angle between the applied force and the distance

• Positive - force and displacement are in the same direction
• Negative - force and displacement are in the opposite direction
• Zero - force is applied, but results in the displacement

Question 12

Define total mechanical energy

Answer 12

Total Mechanical Energy: The sum of the gravitational potential energy and the kinetic energy.

Question 13

Formula for E_p

Answer 13

E_g = mgh (mass x -9.8 x height), J

Question 14

Formula for E_k

Answer 14

E_k = mv²/2, J

Question 15

Explain mechanical efficieny

Answer 15

The ratio of useful energy provided by the device to the energy required to operate the device. For example, a lightbulb produces heat as well as light.

Efficiency = E_out/E_in x 100%

Energy in = the added force’s work, W = F x D

Energy out = potential energy, E_p = mgh

Question 16

What is conduction?

Answer 16

• Process of heat transferring through a substance by the collision of atoms and electrons.
• Conduction occurs best in metals because electrons move more freely. This makes them good conductors of electricity.
• Allows temperature to flow from high to low temperatures.

Question 17

What is convection?

Answer 17

• Transfer of heat by a circulating path.
• Hot air rises because it becomes less dense and cool air falls because it becomes denser.

Question 18

What is radiation?

Answer 18

• Transfer of heat that requires no particles.
• Transferred via electromagnetic waves…
  
  • Visible light
  • Microwaves
  • Radio waves
  • Radar
  • X rays
  • Infrared rays

Question 19

Thermal energy vs. Temperature

Answer 19

Thermal Energy

• Total kinetic and potential energy of the atoms or molecules of a substance.
• Depends on mass, temperature, nature, and state of a given substance.

Temperature

• Measure of the average kinetic energy of the atoms and molecules of a substance, which increases if the motion of the particles increases.

Question 20

Define specific heat capacity:

Answer 20

Specific Heat Capacity: the amount of heat required to raise the temperature of 1.0 kg of that material by 1.0°C

Question 21

Equation for heat transfer:

Answer 21

Q = m•c•∆T, J

Question 22

Equation for heat exchange:

Answer 22

m_hc_h∆Th + m_cc_c∆Tc = 0

Question 23

Work vs. Power

Answer 23

Work versus Power:

• Power is the rate at which WORK is done.
• For example, two individuals of the same mass and height can perform the same amount of work while running 100m, because work is distance x force.
• However, if one individual can complete the 100 m distance in a shorter period of time, they have more power, because to calculate power, work is divided by the time it takes to complete the work.
• Power is measured in Watts (W).

Power = Work/time, W