Pressure in Physics

Study Notes

Pressure

Pressure is defined as force per unit area.
Units for pressure include Pascals (Pa), atmospheres (atm), mmHg, and cmH₂O.
One Pascal is equal to one Newton per square meter (N/m²).
One atmosphere (atm) is equal to 1.013 x 10⁵ Pa, 760 mmHg, or 1033 cmH₂O.
Pressure in a liquid column (P) can be calculated using the formula P = pgh, where p is the density of the liquid, g is the acceleration due to gravity, and h is the height of the column.
Mercury has a density of approximately 13.6 g/cm³ and water has a density of 1 g/cm³. A water column would need to be 13.6 times higher than a mercury column to exert the same pressure.
Blood has a density of approximately 1.06 g/cm³ at 37°C.

Types of Pressures

Blood pressure.
Pressure inside the skull (intracranial pressure).
Eye pressure (intraocular pressure).
Pressure in the skeleton.
Pressure in the urinary bladder.
Ear pressure.
Pressure in the lungs.
Hyperbaric oxygen therapy pressure.
Pressure in the digestive system.

Negative Pressure

Negative pressure is any pressure lower than atmospheric pressure.
During inhalation, the pressure in the lungs must be lower than atmospheric pressure.
The pressure in the lungs during inhalation is a few centimeters of water pressure.

Calculating Atmospheric Pressure

Example calculation: Calculate atmospheric pressure when the height of the mercury column is 76 cm.
P = pgh = 13.6 g/cm³ * 980 cm/s² * 76 cm = 1.013 x 10⁶ dyn/cm² = 1.013 x 10⁵ N/m².

Blood Pressure

Sphygmomanometer is the most common clinical instrument for measuring blood pressure.
Two types of pressure gauges used in sphygmomanometers are mercury manometers and aneroid gauges.
Recently, a digital sphygmomanometer is used.
Blood pressure is a routine clinical measurement of health.
It is measured using a sphygmomanometer, which consists of a cuff, a bulb, and a meter to measure the pressure in the cuff.

Blood Pressure Ranges

Blood pressure is measured in systolic/diastolic form.
Normal blood pressure is less than 120/80 mmHg.
Prehypertension: systolic < 120 and diastolic < 80
Stage 1 High blood pressure : 140-159
Stage 2 High blood pressure: 160 or higher

Measuring Blood Pressure

Blood pressure is measured using a sphygmomanometer.
Measurement takes place at the brachial artery of the upper arm.
Two pressures are recorded: systolic and diastolic.
Systolic pressure occurs during ventricular contraction.
Diastolic pressure occurs between heartbeats, during ventricular relaxation.
Normal blood pressure for young adults is typically 120/75 mm Hg.

Abnormalities of Blood Pressure

Hypertension (high blood pressure): Chronic resting blood pressure greater than 140/90. Can weaken small blood vessels and cause aneurysms.
Hypotension (low blood pressure): Chronic low resting blood pressure, may be caused by blood loss, dehydration, or anemia

Pressure Inside the Skull

The brain is filled with approximately 150 cm³ of cerebrospinal fluid (CSF).
Hydrocephalus is a disorder resulting from blocked CSF flow or trapped CSF in the skull, causing raised intracranial pressure.

Measuring Hydrocephalus

Crude method: Measuring the circumference of the skull above the ear. Normal values for infants are 32-37 cm. Larger head size may indicate hydrocephalus.
Qualitative method (transillumination): Using light scattering properties, method used to evaluate brain fluid levels.

Eye Pressure

The eye contains aqueous and vitreous humors (fluid) that transmit light.
Eye pressure (intraocular pressure) maintains the eye's shape and size.
Normal eye pressure ranges from 12-23 mmHg.
Glaucoma is a condition where fluid drainage is blocked leading to increased pressure and vision impairment. Glaucoma can be mild (tunnel vision) or severe (blindness).

Measuring Eye Pressure

A physician can estimate eye pressure by feeling it with their fingertips.
Tonometers are instruments that precisely measure intraocular pressure.

Description

This quiz explores the concept of pressure, including its definition, units, and calculations. Participants will also learn about various types of pressure and their importance in both physics and biology. Test your understanding of how pressure is measured and its applications in real-life scenarios.