What is Mach 1? Mach Speed is when an object moves faster than the speed of sound. For normal and dry conditions and temperature of 68 degrees F, this is 768 mph, 343 m/s, 1,125 ft/s, 667 knots, or 1,235 km/h.

If you’ve ever watched a movie with fighter jets in it, chances are you’ve heard them talk about Mach numbers. Yet while pilots in these movies will routinely talk about planes traveling at Mach 2 or 3, what does that mean in reality?

As it turns out, Mach numbers don’t indicate a set speed, and two different planes can actually be at the same Mach number while moving at different speeds.

Ultimately, Mach numbers are defined by their relationship to the speed of sound. However, the speed of sound isn’t constant and can actually fluctuate greatly depending on things like the atmospheric conditions observed at a particular place and a particular time.

What Is Mach 1?

Mach numbers were created thanks to the work of Ernst Mach, an Austrian physicist. While Mach contributed much to the fields of cosmology and optics, he was the one to first describe the speed of sound, as well as what happens when an object exceeds the speed of sound. Mach noted that when objects accelerate faster than the speed of sound, an interesting phenomenon occurs.

As an airplane approaches the speed of sound, the sound waves that are emitted by the plane itself cannot get ahead of the plane. This causes the sound waves to pile up and accumulate in a cone of sound which forms directly behind the aircraft.

As the aircraft passes an area, all the accumulated sound is released at once as the cone of sound expands rapidly. This is the mechanism that creates sonic booms.

Mach 1 refers to the point at which an aircraft exceeds the speed of sound, creating a sonic boom. What is the exact speed of sound? That question is more difficult to answer than you would think, as the exact speed of sound is dependent upon a variety of variables, like the current temperature and air pressure of the air the sound is passing through.

As a general rule though, at an air temperature of 0 degrees Celsius (32 degrees Fahrenheit), the speed of sound is approximately 331 meters per second (1,087 feet per second).

In general, sound can travel faster in warmer air, so when the temperature is at 20 degrees Celsius (or 68 degrees Fahrenheit) the speed of sound is at 343 meters (or 1127 feet) a second. Note that the figures given here reflect the speed of sound at sea level, and at higher.

How Fast is Mach 1?

A Mach number is a common ratio unit of speed when one is talking about aircrafts. By definition, the Mach number is a ratio of the speed of a body (aircraft) to the speed of sound in the undisturbed medium through which the body is traveling.

It is said that the aircraft is flying at Mach 1 if its speed is equal to the speed of sound in air (which is 332 m/s or 1195 km/hr or 717 miles/hour.) An aircraft flying at Mach 2 is flying at twice the speed of sound in air, etc. Mach numbers are named after Ernst Mach (1838-1916), an Austrian philosopher and physicist. The term Mach number came into use in 1929.

What Happens When You Break the Sound Barrier?

The Yeager plane wasn’t the first man-made object to travel faster than sound. Cannonballs did it, so did bullets. And even the crack of a bullwhip is caused by the tip moving that fast. But the difficulties of creating an aircraft that could travel so fast led to the idea of a metaphorical “sound barrier” that had to be pushed through.

What actually happens is that as an aircraft approaches Mach 1, the pressure waves that it creates can’t outrace the plane itself. This causes drag and shock waves on the aircraft, making it hard to control. Yeager’s plane had to be modified to counteract this.

When a flying object reaches and exceeds Mach 1, the pressure waves combine into shock waves that are heard as explosion-like sonic booms. A craft flying faster than the speed of sound generates multiple sonic booms along its flight path.

An object that moves slower than the speed of sound is called subsonic. Flying at or near the speed of sound is defined as transonic flight. Speeds between Mach 1 and Mach 5 are called supersonic. And speeds beyond that—the space shuttle, for example, re-enters the earth’s atmosphere at Mach 25—are designated as hypersonic.

When Is It Used, How Useful Is It?

Though we can use the Mach number to measure the speed of any object or vehicle through any medium, we typically use it in aviation for vehicles traveling through the air. This is because it is more useful to measure a vehicle’s speed in units that are both accurate and comprehensible.

Vehicles in aviation can more easily approach speeds that we can measure in terms of the speed of sound. Miles-per-hour does not translate very well to our intuition of travel through air.

Land vehicles do not regularly approach these speeds, so we use a lower unit of speed (miles, kilometers, etc.). Famous exceptions to this include vehicles that are built to break land speed records. These vehicles regularly approach and surpass Mach 1.

Nautical vehicles calculate their speed using knots. This is useful in the Ocean where a vehicle’s surroundings are in constant motion. Due to the resistance and friction inherent in water travel, these vehicles do not approach Mach 1.

The Mach number cannot be used in space. Since sound does not travel through space, it is impossible to calculate the Mach number.

How to Use Mach Number Correctly

It is important to understand that the Mach number is a relative measure of speed. It is not an absolute unit of velocity or distance.

When calculating the Mach number, make sure you use the speed of sound within a similar medium. For example, though an object might travel at 500 miles per hour on Earth and Mars, the Mach number in each location will be different.

It is also best to use the Mach number for objects or vehicles that travel at speeds that make sense to translate into a Mach number. It is not very helpful to describe the speed of a dog in terms of Mach, for instance.

What Mach Is the Speed of Light?

The speed of light is a universal constant. This means that although light may appear to move slower, or propagate more slowly through different states of matter, it does not. It is always traveling at the same speed of 670,616,629 miles per hour, or c.

Using our equation to calculate the Mach number of the speed of light, we get Mach 874,030.49.

As we can see, using Mach to calculate anything relative to the speed of light is beyond reasonable comprehension or comparison. We usually only use the speed of light with anything related to stellar and interstellar sciences and subatomic colliders.

FAQs

What is the speed of Mach 1?

Supersonic speed is the speed of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately 343.2 m/s (1,126 ft/s; 768 mph; 667.1 kn; 1,236 km/h).

What does Mach 1 mean?

A Mach number is the ratio of an object’s speed in a given medium to the speed of sound in that medium. Mach 1, then, is the speed of sound, around 761 mph at sea level on a standard day. The term is also used as a metaphor for high speeds more generally.

What is Mach 1 in an airplane?

By definition, Mach number is a ratio of the speed of a body (aircraft) to the speed of sound in the undisturbed medium through which the body is traveling. It is said that the aircraft is flying at Mach 1 if its speed is equal to the speed of sound in air (which is 332 m/s or 1195 km/hr or 717 miles/hour.)

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