Physics 01
Why Do You Feel Pushed Outward on a Bend?
Nothing pushes you outward on a bend: the car turns and you go straight. Centrifugal vs centripetal force, with numbers for cars, spin cycles and orbits.
calculators
Physics 02
How Does Carbon Dating Work, and How Far Back Can It Go?
Carbon-14 halves every few thousand years, so what is left in a bone or seed gives its age. The maths, the half-life puzzle and the 50,000 year limit.
Space 03
How Long Does Sunlight Take to Reach Earth?
Sunlight takes 8 minutes 19 seconds to reach Earth on average: 8 min 11 s in January, 8 min 27 s in July. The sums, plus light times to planets and stars.
Space 04
How Long Would It Take to Drive to the Moon?
At 100 km/h, a non-stop drive to the Moon takes 160 days, about 5.3 months. Here are the sums, plus walking, flying and Apollo 11 for comparison.
Space 05
How Many Miles Have You Travelled Around the Sun?
Earth carries you 584 million miles round the Sun every year. Work out your lifetime total, see the sums, and learn why galaxy figures cannot be added.
Physics 06
How Many Watts Can a Human Produce? The Stair Test
A sprint up six steps can top one horsepower. How the stair test turns mass, height and time into watts, and how much power people can keep up.
Space 07
How Old Would I Be on Mars? Mars Years Explained
How old you would be on Mars: divide the days you have lived by 686.98. Worked examples, a quick rule, sols, the next Mars birthday and every other planet.
Technology 08
How Random Is Random? Fair Ways to Pick Teams
Why shuffling by sorting, swapping with any position or a remainder trick is quietly unfair, and how a proper shuffle splits a class into groups.
Physics 09
How to Find the Spring Constant (With a Home Experiment)
Find a spring constant with k = F ÷ x: hang known loads, measure the stretch, and take the slope of the graph. A worked home experiment using cups of water.
Space 10
Which Star's Light Left the Year You Were Born?
Vega's light takes 25.0 years to reach us, so a 25-year-old sees light that left the year they were born. Find your birthday star and the sums behind it.
Physics 11
Why Average Speed Is Not the Average of the Speeds
Drive 60 km/h out and 40 km/h back and you average 48, not 50. Why slow legs count for more, the harmonic mean, and pace for runners.
Environment 12
Why Does a Cold Glass Sweat? The Dew Point Explained
The water on a cold glass comes from the air, not the drink. It forms when the glass is colder than the dew point. Here is how to work that out.
Environment 13
Why Does Humid Heat Feel Hotter Than Dry Heat?
Sweat only cools you when it evaporates, and humid air slows that down. The heat index puts a number on it: 32 °C at 70% humidity feels like 40 °C.
Physics 14
Why Does Ice Float? Density Explained With Numbers
Ice floats because it is about 8% less dense than water: 0.917 vs 0.9998 g/cm³. Why that is, how much of an iceberg sits under, and how to measure it.
Physics 15
Why Does Sound Travel Faster in Water and Steel?
Sound is 4 times faster in water and 17 times faster in steel than in air, because stiffness matters more than density. The numbers, worked through.