Twin Paradox Twin paradox started as a contradiction in ‘time delay’ in Special relativity. The Twin Paradox goes something like this: (Contents vary depending on the media.) One of the twins stays on Earth, and the other leaves Earth in … more

## Minkowski Spacetime

Minkowski Spacetime Minkowski spacetime (or Minkowski space) is a coordinate system devised by German mathematician Minkowski. The peculiar thing is that the coordinate system contains space and time. Minkowski spacetime uses matrices to express a four-dimensional coordinate system (x, y, … more

## Special Relativity: Length Contraction

CAUTION: Read the following instructions to the end to get the result that the moving object appears to be constricted in length. (It is difficult to explain ‘Special Relativity’ only with the above simulation.) The meanings of the symbols used … more

## Special Relativity: Time Dilation

The meanings of the symbols used in this simulation are as follows. L = Distance that light travels in a stationary state, (=ct｡) c = Speed of light (≒ 299,792,458 m/s) t｡ = The transit time of light observed inside … more

## Eratosthenes’ Calculation of Earth’s Circumference 2

Eratosthenes’ Calculation of Earth’s Circumference The first person to measure the earth’s size was Eratosthenes, an ancient Greek scientist about 2,000 years ago. Eratosthenes lived in Alexandria, near the Nile River’s mouth by the Mediterranean coast, in northern Egypt. He … more

## How to use a multimeter

Multimeter A multimeter is a measuring device that combines various measurement functions such as voltage, current, and resistance. Multimeters are classified into analog and digital multimeters according to how they operate. Analog multimeters were used a lot in the past, … more

## Structure of an ammeter

Ammeter The strength of the current in the electrical circuit is measured using an ammeter. There is a rotor with a coil wound inside the ammeter. When the current flows through the ammeter, the coil and the rotor will have … more

## Gulliver’s Nutrition

Why did the King of Lilliput serve 1728 meals to Gulliver? This is because the volume of two objects that resemble each other in three dimensions is proportional to the cube of length. Since Gulliver’s height is about 12 times … more

## Spring Scales

A spring scale is a tool that measures the mass and gravity of an object using the spring’s elastic force. The spring of this scale is lengthened by gravity and shortened by elasticity. You can find out the gravity (or … more

## Doppler Effect

Doppler Effect We have heard an ambulance siren and felt that the ambulance is getting closer. When the ambulance approaches, the sirens sound higher, and when they move away, the sirens sound lower. That is, when an ambulance approaches with … more

## Eratosthenes’ Calculation of Earth’s Circumference

Eratosthenes’ Calculation of Earth’s Circumference The first person to measure the earth’s size was Eratosthenes, an ancient Greek scientist about 2,000 years ago. Eratosthenes lived in Alexandria, near the Nile River’s mouth by the Mediterranean coast, in northern Egypt. He … more

## Archimedes Buoyancy 2

Why is the submerged volume important to understand buoyancy? It is so famous that the 3rd-century Greek philosopher Archimedes shouted “Eureka!” and ran out of the bathhouse naked. （What did Archimedes find out? – Quotations from middle school science textbooks） … more