Physics Calculators
Free calculators for the formulas that come up most in school physics: speed, distance and time, kinetic and potential energy, power, Ohm's law and the dew point.
6 calculators each one also works as a widget
- Speed Distance Time Calculator Fill in any two of speed, distance and time to get the third, with travel time in hours and minutes.
- Kinetic Energy Calculator Kinetic energy of a moving object from its mass and speed (KE = ½mv²).
- Dew Point Calculator Dew point from the air temperature and the relative humidity.
- Gravitational Potential Energy Calculator Potential energy of an object from its mass and height (PE = mgh).
- Mechanical Power Calculator Power from work and time, force and speed, or voltage and current, in watts or horsepower.
- Ohm's Law Calculator Find voltage, current, resistance or power from any two of them.
Which Physics Calculator Do You Need?
Most physics problems give you some quantities and ask for one more. Pick the calculator for the relationship the problem is about, enter the values you have, and it works out the one you are missing.
Motion problems (how fast, how far, how long) use the Speed Distance Time Calculator. Fill in any two and it gives the third, with the travel time written in hours and minutes.
Energy problems use KE = ½mv² for a moving object and PE = mgh for an object raised above the ground. The Kinetic Energy and Gravitational Potential Energy calculators take the mass and the speed or the height. Power is how fast that energy is used, and the Mechanical Power Calculator finds it from work and time, force and speed, or voltage and current.
Circuit questions use Ohm's law, V = IR, together with P = VI. The Ohm's Law Calculator takes the values you know and finds voltage, current, resistance and power. The Dew Point Calculator answers a weather question instead: the temperature at which the air is saturated and water starts to condense.
Keep the Units Consistent
Kilograms, meters and seconds give answers in joules and watts. If your numbers come in grams, kilometers or hours, convert them first, or pick the unit in the calculator where it offers a choice. Mixing grams with kilograms, or minutes with seconds, is an easy way to get an answer that is a thousand or sixty times off.
A Worked Example
A 1,000 kg car moving at 20 m/s (72 km/h) has a kinetic energy of ½ × 1,000 × 20² = 200,000 J, or 200 kJ. Lifting the same car 10 m would give it a potential energy of 1,000 × 9.81 × 10 = 98,100 J. If the engine supplies those 200 kJ in 10 seconds, its power is 200,000 ÷ 10 = 20,000 W, which is 20 kW or about 27 horsepower.
Each step uses one of the calculators on this page, and each calculator page shows its own worked examples, so you can check a homework answer one stage at a time.
Frequently Asked Questions
What is the formula for speed?
Speed = distance ÷ time. Rearranged, distance = speed × time and time = distance ÷ speed. At 60 mph, 150 miles take 150 ÷ 60 = 2.5 hours, which is 2 h 30 min.
What is the difference between kinetic and potential energy?
Kinetic energy is the energy of motion, ½mv². Gravitational potential energy is the energy an object has because of its height, mgh. A falling ball turns its potential energy into kinetic energy as it speeds up.
How do I use Ohm's law?
Ohm's law says voltage equals current times resistance, V = I × R. A 12 V battery across a 4 Ω resistor drives a current of 12 ÷ 4 = 3 A, and the resistor uses 12 × 3 = 36 W of power.