Featured contributor PhD Applied Physics; former research associate at a national metrology lab.

Dr. Helena Ortiz

Senior Reviewer, Science & Engineering

0 calculators 0 articles Member since Jun 2026

About

Helena is the senior technical reviewer for physics, chemistry, and unit-conversion calculators. She is the last pair of eyes on every formula — checking constants, units, and edge cases against primary sources and standards bodies.

She holds a PhD in Applied Physics and previously held a research post at a national metrology lab.

Areas of expertise

Physics Chemistry Unit conversion Measurement standards

Education & credentials

BSc Physics — Universidad Complutense de Madrid
PhD Applied Physics — Stanford University

Physics / Mechanics

Wedge Mechanical Advantage Calculator

Compute the ideal mechanical advantage of a wedge from its slope length L (the distance the wedge is driven) and its thi...

basic

8,640 4.3 1 min

Physics

Vis-Viva Elliptical Orbit Velocity Calculator

Compute the orbital speed at distance r from the central body for an elliptical orbit of semi-major axis a, using the vi...

basic

3,420 4.8 1 min

Physics

Electric Potential Energy of Two Point Charges Calculator

Calculates the electric potential energy U = k·q₁·q₂/r between two point charges and the electric force F = k·q₁·q₂/r²....

basic

3,611 4.8 1 min

Chemistry

Density from Molar Mass and Molar Volume Calculator

Compute the mass density of a substance from its molar mass M and molar volume Vm: ρ = M / Vm. For an ideal gas at STP,...

basic

18,527 4.8 1 min

Chemistry

Internal Energy Change ΔU Calculator

Compute the change in internal energy ΔU of a closed system using the first law of thermodynamics, ΔU = q + w, with the...

basic

8,263 4.3 1 min

Chemistry

Integrated Rate Law — Zero-Order Reaction Calculator

Compute the concentration of reactant A at time t for a zero-order reaction: [A] = [A]₀ − k · t. Also reports the time a...

basic

6,181 4.8 1 min

Sports

Wrestling Weight Cut Hydration Calculator

Calculates the weight to lose for a weight class, estimated water deficit, and recommended rehydration volume for wrestl...

basic

992 4.6 1 min

Sports

Sweat Rate and Fluid Replacement Calculator

Calculates sweat rate = (pre_weight − post_weight + fluid_consumed) / exercise_hours. Recommends fluid replacement per h...

basic

15,774 4.1 1 min

Chemistry

pH after Mixing Two Strong-Acid Solutions Calculator

Compute the resultant pH after mixing two strong-acid solutions of arbitrary molarity and volume. Strong acids fully dis...

basic

16,661 4.6 1 min

Chemistry

Moles of Gas Collected Over Water from Total Pressure and Volume Calculator

Compute the moles of dry gas collected by water displacement: subtract the water-vapour partial pressure at the experime...

basic

9,513 4.9 1 min

Physics / Mechanics

Torque from Force and Lever Arm Calculator

Compute the torque produced by a force applied to a lever arm at an angle: τ = F · r · sin θ. Reports the torque in N·m,...

basic

20,569 4.0 1 min

Physics / Mechanics

Lever Mechanical Advantage Calculator

Compute the mechanical advantage of a class-1 lever from the effort and load arm lengths, plus the effort force required...

basic

22,539 4.4 1 min

Showing 193 to 204 of 504 results

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Reviewed by Dr. Helena Ortiz

These calculators were technically reviewed by Dr. Helena Ortiz for accuracy.

Chemistry / Reactions

Equilibrium Constant Calculator

Compute the equilibrium constant K_c from the concentrations of two products (with stoichiometric coefficients 1) divide...

basic

5,060 4.0 1 min

Conversions / Length

Length Converter

Convert between meters, kilometers, miles, feet, inches, and yards.

Featured basic

4,965 4.2 1 min

Chemistry / Solutions

Combined Gas Law Calculator

Find the missing pressure, volume, or temperature using the combined gas law for a fixed amount of gas.

basic

5,360 4.2 1 min

Physics / Electricity

Capacitance Calculator

Compute the capacitance of a parallel-plate capacitor from plate area, plate separation, and the dielectric constant.

basic

12,524 4.1 1 min

Chemistry / Solutions

pOH Calculator

Compute pOH from hydroxide ion concentration and the matching pH at 25 °C.

basic

18,221 4.2 1 min

Ecology / Carbon Footprint

Carbon Footprint Calculator

Estimate your annual personal CO₂e footprint from home energy, driving, flying, and diet — with adjustable emission fact...

Featured basic

15,826 4.9 1 min

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Dr. Helena Ortiz

Wedge Mechanical Advantage Calculator

Vis-Viva Elliptical Orbit Velocity Calculator

Electric Potential Energy of Two Point Charges Calculator

Density from Molar Mass and Molar Volume Calculator

Internal Energy Change ΔU Calculator

Integrated Rate Law — Zero-Order Reaction Calculator

Wrestling Weight Cut Hydration Calculator

Sweat Rate and Fluid Replacement Calculator

pH after Mixing Two Strong-Acid Solutions Calculator

Moles of Gas Collected Over Water from Total Pressure and Volume Calculator

Torque from Force and Lever Arm Calculator

Lever Mechanical Advantage Calculator

Reviewed by Dr. Helena Ortiz

Equilibrium Constant Calculator

Length Converter

Combined Gas Law Calculator

Capacitance Calculator

pOH Calculator

Carbon Footprint Calculator