Question

Each night you measure your height just before going to bed. When you arise each morning, you measure your height again and consistently find that you are 1 inch taller than you were the night before but only as tall as you were 24 hours ago! Is what happens to your body in this instance best described as a physical change or a chemical change? Be sure to try this activity if you haven't already.

Short answer

This phenomenon is best described as a physical change.

Step-by-step solution

Understanding the Phenomenon

When you lie down to sleep, the force of gravity is lessened because you're horizontal, relieving pressure on your spine. This results in slight lengthening, as the spinal discs absorb fluids and expand, making you slightly taller in the morning.

Define Physical Change

Physical changes are changes affecting the form of a chemical substance, but not its chemical composition. Commonly, these changes are reversible and include changes in physical state or form, such as melting, freezing, or lengthening due to external forces.

Define Chemical Change

Chemical changes result in the formation of new chemical substances. This change involves making or breaking of bonds between atoms and is often non-reversible, such as rusting, burning, or digestion.

Identify the Type of Change

The change in your height is due to physical factors (gravity and the state of your spine) and is entirely reversible when you stand up again, as your height returns to normal. No new substances are formed; only the shape and form of your spine temporarily changes.

Conclude the Type of Change

Since the height difference is due to reversible adjustments in the shape of spinal discs without changing the chemical structure, it is best described as a physical change.

Key concepts

Spinal Discs

Spinal discs are the cushioning pads located between the bones of your spine, known as vertebrae. These flexible discs act as shock absorbers, allowing for movement and flexibility while protecting the spinal column.

Each disc is composed of a tough outer layer known as the annulus fibrosus, and a gel-like center called the nucleus pulposus. This structure allows the discs to withstand the compressive forces exerted on the spine throughout the day.

When you lie down at night, the pressure on the spinal discs decreases because gravity is no longer compressing them with the same force. This allows them to expand slightly as they absorb fluid, temporarily increasing your height.

Gravity Effects on Body

Gravity is the force that pulls objects towards the center of the Earth, and it has a significant impact on our bodies, particularly the spine.

Throughout the day, gravity compresses the spinal discs by exerting downward pressure on them, which can cause a mild decrease in height. This is why you might notice you're slightly shorter at nighttime compared to the morning.

When you are lying down, gravity's downward pull on your spine is reduced, allowing the spinal discs to decompress and regain fluid, resulting in a rise in height by morning.

Physical vs Chemical Change

Physical changes and chemical changes are two fundamental types of changes that matter undergoes.

**Physical Change**: This involves changes in the state or form of a substance without altering its chemical identity. Such changes are often reversible. Examples include melting, freezing, and physical deformations like the expansion of spinal discs.

**Chemical Change**: In contrast, this involves the creation of a new chemical substance, with changes in molecular composition and structure. Chemical changes are typically irreversible, such as burning wood or rusting iron.

The height difference observed in the morning after sleeping is a physical change because only the arrangement and volume of your spinal discs change, not their chemical composition.

Reversible Changes

Reversible changes are those that can be undone, returning the material or system to its original state. These are characteristic of most physical changes.

In the context of the human body, reversible changes can be observed when spinal discs expand overnight and return to their normal state after standing.

Other examples of reversible physical changes include melting ice or stretching a rubber band. The key factor in a reversible change is that no permanent alteration occurs to the material at a molecular level.

Anatomy and Physiology

Anatomy and physiology are fields of study that explore the structure and function of the body.

**Anatomy** looks at body structure and form, such as the layout and interrelationship of the spine and spinal discs.

**Physiology** explores the bodily functions and processes, such as how gravity affects the spine or how physical changes like disc compression can impact height.

Understanding these concepts provides insight into how our bodies react to external forces like gravity, and how complex structures like the spinal column are designed to adapt to daily physical demands.