Why the HESI A2 Physics Section Matters
Not every nursing program requires the Physics section of the HESI A2, but if yours does, it can feel intimidating — especially if it has been a while since your last physics class. The good news? The HESI A2 Physics section focuses on conceptual understanding rather than complex calculations, and the topics are directly relevant to how the human body works.
Understanding physics helps nurses grasp fluid dynamics (IV drip rates), pressure changes (blood pressure, ventilators), radiation safety, and body mechanics for patient lifting. This guide breaks every major topic into digestible sections so you can study efficiently and score confidently.
What to Expect on the HESI A2 Physics Section
The Physics section typically contains 25 questions and covers fundamental physics concepts. You will have a calculator available, but most problems require you to apply formulas and reason through scenarios rather than crunch heavy numbers.
The section is organized around these core areas:
- Motion and Forces — speed, velocity, acceleration, Newton's Laws
- Energy and Work — kinetic energy, potential energy, conservation of energy
- Waves and Sound — frequency, wavelength, Doppler effect
- Electricity — current, voltage, resistance, Ohm's Law
- Thermodynamics — heat transfer, specific heat, phase changes
- Optics and Light — reflection, refraction, lenses
- Pressure and Fluids — Pascal's Law, buoyancy, hydraulics
Motion and Forces
Speed, Velocity, and Acceleration
These three concepts describe how objects move. Though they sound similar, each has a specific meaning:
- Speed = distance ÷ time (scalar — no direction). Example: 60 mph.
- Velocity = displacement ÷ time (vector — includes direction). Example: 60 mph north.
- Acceleration = change in velocity ÷ time. Measured in m/s². Negative acceleration is called deceleration.
Key Formula: v = v₀ + at — final velocity equals initial velocity plus acceleration multiplied by time.
Practice Problem: A car accelerates from rest at 3 m/s² for 5 seconds. What is its final velocity?
Solution: v = 0 + (3)(5) = 15 m/s
Newton's Three Laws of Motion
Newton's Laws form the backbone of classical mechanics and appear frequently on the HESI A2:
First Law (Inertia): An object at rest stays at rest, and an object in motion stays in motion at a constant velocity, unless acted upon by an unbalanced force. Nursing connection: A patient on a stretcher will slide forward when the stretcher suddenly stops — this is inertia.
Second Law (F = ma): Force equals mass times acceleration. The heavier an object, the more force is needed to accelerate it. Nursing connection: Lifting a heavier patient requires proportionally more force.
Third Law (Action-Reaction): For every action, there is an equal and opposite reaction. Nursing connection: When you push down on a wheelchair brake, the ground pushes back with equal force, holding the chair in place.
Gravity and Free Fall
All objects near Earth's surface experience gravitational acceleration of approximately 9.8 m/s² (often rounded to 10 m/s² on the exam). In free fall, air resistance is ignored and all objects accelerate at the same rate regardless of mass.
Key Formula: W = mg — Weight equals mass times gravitational acceleration.
Energy and Work
Work
In physics, work is done when a force moves an object through a distance:
Formula: W = F × d × cos(θ)
If you push a cart with 50 N of force for 10 meters in the direction of motion (θ = 0°), the work done is 500 Joules.
Kinetic and Potential Energy
- Kinetic Energy (KE) = ½mv² — energy of motion. A faster or heavier object has more KE.
- Potential Energy (PE) = mgh — stored energy due to height. A patient on a high bed has more gravitational PE than one on a low bed.
Conservation of Energy
Energy cannot be created or destroyed — it only changes form. A ball rolling down a ramp converts PE to KE. At the top, PE is maximum and KE is zero. At the bottom, KE is maximum and PE is zero. The total energy stays constant (ignoring friction).
Practice Problem: A 2 kg book sits on a shelf 3 m high. What is its potential energy? (Use g = 10 m/s²)
Solution: PE = (2)(10)(3) = 60 Joules
Power
Formula: P = W ÷ t — Power is the rate of doing work, measured in Watts. A nurse who lifts a patient faster uses more power (even if the total work is the same).
Waves and Sound
Wave Properties
A wave transfers energy without transferring matter. Key wave properties include:
- Wavelength (λ) — distance between two consecutive peaks
- Frequency (f) — number of wave cycles per second, measured in Hertz (Hz)
- Amplitude — height of the wave from the rest position, related to loudness (sound) or brightness (light)
- Speed — how fast the wave travels through a medium
Key Formula: v = fλ — wave speed equals frequency times wavelength.
Sound Waves
Sound is a longitudinal wave that requires a medium (air, water, tissue) to travel. It cannot travel through a vacuum. Sound travels fastest through solids, then liquids, then gases.
Nursing connection: Stethoscopes work because sound waves from the heart and lungs travel through body tissue and air to the earpieces.
The Doppler Effect
When a sound source moves toward you, the frequency increases (higher pitch). When it moves away, the frequency decreases (lower pitch). This is why an ambulance siren sounds higher as it approaches and lower as it passes. Nursing connection: Doppler ultrasound uses this principle to measure blood flow velocity.
Electricity
Current, Voltage, and Resistance
- Current (I) — flow of electric charge, measured in Amperes (A)
- Voltage (V) — electrical potential difference, measured in Volts (V). Think of it as the "pressure" pushing electrons through a wire.
- Resistance (R) — opposition to current flow, measured in Ohms (Ω)
Ohm's Law: V = IR — Voltage equals current times resistance. This is probably the most tested electricity formula on the HESI A2.
Practice Problem: A circuit has a voltage of 12 V and a resistance of 4 Ω. What is the current?
Solution: I = V/R = 12/4 = 3 Amperes
Series vs. Parallel Circuits
- Series: Components connected end-to-end. Current is the same through all components. If one breaks, the circuit stops.
- Parallel: Components connected on separate branches. Voltage is the same across each branch. If one branch breaks, others still work.
Nursing connection: Hospital electrical systems use parallel circuits so that one piece of equipment failing does not shut down everything in the room.
Thermodynamics
Heat and Temperature
Temperature measures the average kinetic energy of molecules. Heat is the transfer of thermal energy from a warmer object to a cooler one. They are related but not the same — a bathtub of warm water contains more heat than a cup of boiling water, even though the boiling water has a higher temperature.
Methods of Heat Transfer
- Conduction — direct contact (touching a hot pan). Solids conduct best.
- Convection — movement of heated fluid or gas (warm air rising from a radiator).
- Radiation — electromagnetic waves (warmth from the sun). No medium required.
Nursing connection: Warming blankets use conduction; incubators for premature infants use convection and radiation.
Specific Heat Capacity
Formula: Q = mcΔT — heat energy equals mass × specific heat × change in temperature. Water has a very high specific heat (4.18 J/g°C), which is why the human body (60% water) resists rapid temperature changes.
Pressure and Fluids
Pressure
Formula: P = F/A — Pressure equals force divided by area. This explains why sharp needles penetrate easily (small area = high pressure) and why wide mattresses reduce bedsore risk (large area = low pressure).
Pascal's Law
Pressure applied to a confined fluid is transmitted equally throughout the fluid. This principle is used in hydraulic lifts and syringes. When you press the plunger of a syringe, the pressure is transmitted to the fluid inside, pushing the medication out.
Buoyancy (Archimedes' Principle)
An object submerged in fluid experiences an upward buoyant force equal to the weight of the fluid displaced. Objects float when the buoyant force exceeds their weight. Nursing connection: Hydrotherapy and aquatic physical therapy reduce stress on joints because buoyancy supports the patient's weight.
Optics and Light
Reflection and Refraction
- Reflection — light bounces off a surface. The angle of incidence equals the angle of reflection.
- Refraction — light bends when it passes from one medium to another (air to water). This is why a straw in a glass of water looks bent.
Lenses
- Convex (converging) lenses focus light to a point — used in magnifying glasses and the human eye.
- Concave (diverging) lenses spread light apart — used to correct nearsightedness.
Essential Physics Formulas Cheat Sheet
Memorize these formulas before test day:
- Speed:
v = d/t - Acceleration:
a = Δv/t - Force:
F = ma - Weight:
W = mg - Work:
W = Fd - Power:
P = W/t - Kinetic Energy:
KE = ½mv² - Potential Energy:
PE = mgh - Wave Speed:
v = fλ - Ohm's Law:
V = IR - Heat:
Q = mcΔT - Pressure:
P = F/A - Density:
ρ = m/V
Top Study Strategies for HESI A2 Physics
- Focus on concepts, not calculations. The HESI tests whether you understand why things happen more than whether you can grind through math.
- Connect physics to nursing. Every topic has a real-world medical application. When you link a formula to a clinical scenario, it sticks.
- Memorize the formula sheet above. Write each formula 5 times, then work a practice problem for each.
- Use elimination on the exam. Many physics questions include units in the answer choices — if your units do not match, eliminate that option.
- Practice unit conversions. Know how to convert between metric units (cm to m, g to kg) because the HESI sometimes requires it mid-problem.
- Don't overthink it. The HESI A2 tests introductory-level physics. If your calculation requires calculus or advanced trig, you are probably on the wrong track.
Practice Quiz: Test Your Physics Knowledge
Try these five questions before you move on:
1. A 5 kg box is pushed across a floor with a force of 20 N. What is its acceleration?
Answer: a = F/m = 20/5 = 4 m/s²
2. A wave has a frequency of 500 Hz and a wavelength of 0.68 m. What is its speed?
Answer: v = fλ = (500)(0.68) = 340 m/s (approximately the speed of sound in air)
3. How much heat is needed to raise 200 g of water by 15°C? (c = 4.18 J/g°C)
Answer: Q = mcΔT = (200)(4.18)(15) = 12,540 Joules
4. A circuit has a current of 2 A and a resistance of 6 Ω. What is the voltage?
Answer: V = IR = (2)(6) = 12 Volts
5. Which of Newton's Laws explains why passengers lurch forward when a bus stops suddenly?
Answer: Newton's First Law (Inertia) — the passengers' bodies tend to stay in motion even after the bus stops.
Final Thoughts
The HESI A2 Physics section is highly manageable when you break it into its core topics and connect each one to real nursing scenarios. Focus your study time on the formula sheet, work through practice problems, and remember that this section rewards understanding over memorization. With consistent practice, you'll walk into test day feeling confident and prepared.