Heat and Temperature: Thermal Equilibrium, Transfer, and Effects
Heat and Temperature
Thermal Equilibrium and the Concept of Temperature
When we describe a body as hot or cold, we are referring to its temperature. We can measure temperature using a thermometer.
Thermal Equilibrium
Two bodies are in thermal equilibrium when they have the same temperature. Thermometers measure temperature by reaching thermal equilibrium with the object they are measuring.
Bodies are considered hot or cold when their temperature is high or low, respectively. Bodies in thermal equilibrium have the same temperature.
Thermal Imbalance and the Concept of Heat
Two bodies are in thermal imbalance when they have different temperatures.
Heat always flows from the body with a higher temperature to the body with a lower temperature. If both bodies have the same temperature, there is no heat transfer.
Heat is measured in Joules, and its value represents the energy transferred from the hotter body to the colder body.
Do bodies “have” heat?
No, bodies possess thermal energy. They can either absorb heat or release it when they come into contact with other bodies at different temperatures. We can say that bodies are hot or that they give off heat, but not that they “have” heat.
Effects of Heating: Fundamentals of Thermometers
Thermal Expansion
Generally, bodies expand when their temperature increases. This increase in volume is called thermal expansion. Gases expand significantly more than liquids and solids.
Mercury Thermometers
When the temperature of a mercury thermometer increases, the mercury expands and rises in the tube. Each level in the thermometer corresponds to a specific temperature value.
How is Heat Transferred?
Heat transfer can occur without mass transfer (conduction), with the movement of matter (convection), and without matter (radiation).
Does Cold Exist?
Cold is not a separate entity but rather the absence of heat. We perceive objects as cold when their temperature is lower than our skin temperature.
Changes of State
Melting Point: The temperature at which a substance changes from a solid to a liquid state.
Boiling Point: The temperature at which a substance changes from a liquid to a gaseous state.
During changes of state in pure substances, the temperature remains constant. However, the energy content of steam is higher than that of liquid, and the energy content of liquid is higher than that of solid, even at the same temperature.
Biological Responses to Stimuli
Functions of Living Organisms
- Collecting environmental information (both external and internal): Sensory organs
- Processing information: Nervous system
- Developing and executing responses: Locomotor system and glands
Stimulus and Response
Stimulus: A physical or chemical change in the environment capable of eliciting a response.
Behavior: A sequence of actions in response to a stimulus (e.g., crying).
Response: The most visible part of the stimulus-response relationship. Carried out by effector organs:
- Motor responses: Conducted by the locomotor system.
- Glandular responses: Glands produce and secrete substances.
Receptors: Structures specialized in detecting stimuli.
Effectors: Organs that carry out the response.
Proprioceptive Senses: Detect stimuli from inside the body (e.g., balance, hunger, thirst).
Types of Stimuli
- Chemical: Caused by chemicals:
- Contact: Taste
- Distance: Smell
- Thermal: Related to heat and cold (e.g., touch, heat pits).
- Mechanical: Provoked by touch or pressure (e.g., touch, hearing, lateral line).
- Light: Related to light (photoreceptors).
The Nervous System
Communication between receptors and effectors is carried out by the nervous system, which consists of nerves and nerve centers. This communication is very fast and efficient.
Central Nervous System: Receives information from receptors and produces responses. It has memory.
Neurons: Cells of the nervous system that process information and transmit nerve impulses.
Synapses: Connections between neurons.
Nerves: Communicate receptors with nerve centers. Transmit information.
Vertebrates: Brain – Spinal cord
Invertebrates: Brain – Ganglia chain
Types of Nerve Fibers
- Sensory: Transmit information from receptors to the nerve center.
- Motor: Transmit information from the nerve center to effector organs.
- Mixed: Carry both types of information.
Communication Without Nerves
Chemical messages, carried by the endocrine or hormonal system through glands that secrete hormones into the bloodstream.
Endocrine Glands: Release hormones into the bloodstream (e.g., pituitary gland).
Exocrine Glands: Release substances through ducts (e.g., sweat glands).
The nervous and endocrine systems are coordinated by the hypothalamus. They are interdependent.
Behavior in Plants
Plants lack sense organs but can still receive stimuli and respond to them.
Tropism
Tropism: A change in plant growth caused by a stimulus. It is a slow response.
- Phototropism: The stimulus is light. The plant grows towards the light source.
- Geotropism: The stimulus is gravity. Regardless of the seed’s position, the stem grows upwards, and the root grows downwards.
- Hydrotropism: The stimulus is water. The roots grow towards the water source.
Some plants secrete irritants. Others respond to pressure stimuli (e.g., carnivorous plants).
Motion Formulas
Displacement: The difference between the final position and the initial position of an object.
Distance Traveled: The length of the path measured along the path.
Formula for Distance: D = x2 – x1 (x1: starting position, x2: ending position)
Speed: Indicates how fast an object moves.
Formula for Speed: V = d / t (d: displacement, t: time)