Physics Calculators
Solve physics and electrical engineering problems with our free physics calculators. From horsepower and engine performance to Ohm's law and radioactive decay, these tools provide instant results with formula breakdowns and real-world context for students, engineers, and science enthusiasts.
Half-Life Calculator
Calculate the half-life of a substance or the remaining amount after a given number of half-lives.
Horsepower Calculator
Calculate horsepower from torque and RPM or convert between horsepower units.
Engine Horsepower Calculator
Estimate engine horsepower based on vehicle weight, quarter-mile time, or dyno data.
Ohms Law Calculator
Calculate voltage, current, resistance, and power using Ohm's law equations.
Voltage Drop Calculator
Calculate voltage drop across wires based on wire gauge, length, and current load.
Resistor Calculator
Decode resistor color bands and calculate resistance values for series and parallel circuits.
How to Choose the Right Physics Calculator
Start with the horsepower calculator for straightforward power unit conversions between horsepower, watts, and kilowatts. It handles mechanical, electrical, and boiler horsepower variants and is useful for comparing equipment ratings across different measurement systems.
The engine horsepower calculator is specifically designed for automotive applications. It estimates engine output based on displacement, RPM, and efficiency factors, making it valuable for car enthusiasts, mechanics, and anyone evaluating engine performance modifications.
For electrical circuit analysis, the Ohm's law calculator is the fundamental tool. Enter any two of voltage, current, resistance, or power, and it calculates the rest. The voltage drop calculator extends this to real-world wiring scenarios, helping electricians and DIY enthusiasts ensure their wire runs meet safety codes. The resistor calculator is essential for electronics hobbyists and engineers who need to decode color bands or calculate equivalent resistance for combined resistors.
The half-life calculator addresses exponential decay problems across multiple disciplines. Use it for radioactive decay calculations in physics, drug metabolism rates in pharmacology, or carbon-14 dating estimations in archaeology.
Understanding Physics and Its Applications
Physics is the fundamental natural science that studies matter, energy, and the interactions between them. It seeks to understand everything from the smallest subatomic particles to the largest structures in the universe, using mathematical models and experimental observation. The calculators in this section focus on mechanics (power and work) and electromagnetism (circuits and resistance), two of the most practically applicable branches of physics.
Power measures the rate at which work is done or energy is transferred. One horsepower, originally defined by James Watt as the power a horse can sustain, equals approximately 746 watts. In automotive contexts, horsepower quantifies engine output, while in electrical contexts, power (measured in watts) equals voltage times current (P = VI). Understanding power relationships is essential for sizing motors, generators, electrical systems, and heating or cooling equipment.
Ohm's law (V = IR) is the foundational relationship in electrical engineering. It states that the voltage across a conductor is proportional to the current flowing through it, with resistance as the proportionality constant. Combined with the power formula (P = IV), these relationships allow you to analyze any simple DC circuit. Real-world applications include designing circuits, sizing wires to prevent overheating, selecting appropriate fuses, and troubleshooting electrical problems.
Radioactive decay is a quantum mechanical process where unstable atomic nuclei lose energy by emitting radiation. The half-life is the time required for half of a radioactive substance to decay. This concept follows an exponential decay curve: N(t) = N0 x (1/2)^(t/t_half). Half-life applications extend far beyond nuclear physics into medicine (imaging and therapy dosing), archaeology (carbon-14 dating), geology (rock age determination), and environmental science (contamination remediation timelines).
Frequently Asked Questions
How do I convert horsepower to watts?
One mechanical horsepower equals approximately 745.7 watts. Multiply the horsepower value by 745.7 to get watts, or by 0.7457 to get kilowatts. For example, a 200 HP engine produces approximately 149,140 watts or 149.1 kilowatts. Note that electrical horsepower is slightly different at 746 watts. Our horsepower calculator handles all variants automatically.
How does Ohm's law work?
Ohm's law states that voltage (V) equals current (I) times resistance (R): V = IR. This means if you know any two values, you can calculate the third. For example, a 12V battery pushing current through a 4-ohm resistor produces 3 amps of current (12/4 = 3). Combined with the power formula P = IV, you can calculate all four electrical properties from just two known values.
What is voltage drop and why does it matter?
Voltage drop is the reduction in voltage as electrical current flows through a wire. Longer wires, thinner wires, and higher currents all increase voltage drop. Excessive voltage drop (typically above 3% for branch circuits per NEC recommendations) can cause equipment to malfunction, lights to dim, and motors to overheat. Our calculator helps you select the right wire gauge for your installation distance and current load.
How do I read resistor color bands?
Resistor color bands encode the resistance value using colors. For a 4-band resistor: the first two bands are digits, the third is the multiplier (number of zeros), and the fourth is tolerance. For example, Red-Violet-Orange-Gold means 27 x 1,000 = 27,000 ohms (27k) with 5% tolerance. Colors map to digits: Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9.
How is half-life used in carbon dating?
Carbon-14 has a half-life of approximately 5,730 years. Living organisms maintain a constant level of C-14 through metabolism, but after death, the C-14 decays without being replenished. By measuring the remaining C-14 in an artifact and comparing it to the expected level in living tissue, scientists can estimate how long ago the organism died. This method is reliable for materials up to about 50,000 years old.