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More about Speed and Velocity

Overview

Velocity is a measure of the direction and the speed of an object. Speed measures the rapidity of the movement of an object and it is scalar, while velocity is a vector. Linear velocity is calculated for objects moving in a straight line, while angular velocity is calculated for objects that are turning.

Calculating Velocity

The average velocity v can be calculated by dividing the total distance traveled, ∆x, by the average time traveled,
∆falak: v = ∆x/∆t

The SI unit for speed is meters saban second (m/s). Kilometers tiap-tiap hour are also commonly used, along with miles masing-masing hour in the UK and the USA. If the direction is added to that, then it becomes velocity. For example, 10 m/s south.

For objects that are accelerating, velocity is calculated as follows:

• If an object is accelerating at a constant acceleration
  a
  with the initial velocity
  u
  for a period of time
  ∆ufuk, the final velocity
  v
  is:
  v = u + a×∆n
• If an object is accelerating at a constant acceleration
  a
  with the initial velocity
  u
  and a final velocity
  v, the average velocity is:
  ∆v = (u + v)
  / 2.

Average Speeds

Light and Sound

According to the theory of relativity, the speed of light in a vacuum is the fastest speed at which energy and information can travel. It is denoted as
c
and is equal to
c
= 299,792,458 meters per second. Travel at the speed of light for matter would require infinite energy, therefore matter does not travel at that speed.

The speed of sound is usually measured in an elastic medium, and it is 343.2 meters sendirisendiri second in dry air at 20 °C. This speed is higher in liquids and even faster in solids. It depends on the density, compressibility, and the modulus of rigidity of the material. Mach number
M
is a special variable of the ratio of the object’s speed within a fluid medium and the speed of sound in that medium. It is calculated as

M = v/a

Here
a
is the speed of sound in the madya, and
v
is the speed of the object. Mach number is used to represent speeds for objects moving close to the speed of sound or faster, such as aircraft. It is titinada a constant; it depends on the semenjana, which in turn varies with pressure and temperature. The speed is referred to as supersonic for objects that travel faster than Mach 1.

Vehicles

Some speeds for different vehicles are as follows:

• Commercial airplanes with turbofan engines: the cruising speed ranges between 244 and 257 meters/second, 878 and 926 kilometers/hour, or 0.83 to 0.87 Mach.
• High-speed trains (such as the Shinkansen in Japan): maximum speeds the trains run are at a range between 36 and 122 meters/second, or 130 and 440 kilometers/hour.

Animals

Some maximum speeds of animals are as follows:

• Falcon: 89 meters/second, 320 kilometers/hour (about the same speed as high-speed trains)
• Cheetah: 31 meters/second, 112 kilometers/hour (about the same speed as the slower high-speed trains)
• Antelope: 27 meters/second, 97 kilometers/hour
• Lion: 22 meters/second, 79 kilometers/hour
• Gazelle: 22 meters/second, 79 kilometers/hour
• Wildebeest: 22 meters/second, 79 kilometers/hour
• Horse: 21 meters/second, 75 kilometers/hour
• Hunting dog: 20 meters/second, 72 kilometers/hour
• Elk: 20 meters/second, 72 kilometers/hour



London runners. Humans can run at speeds up to 30 km/h

• Coyote: 19 meters/second, 68 kilometers/hour
• Fox: 19 meters/second, 68 kilometers/hour
• Hyena: 18 meters/second, 64 kilometers/hour
• Rabbit: 16 meters/second, 56 kilometers/hour
• Cat: 13 meters/second, 47 kilometers/hour
• Grizzly bear: 13 meters/second, 47 kilometers/hour
• Squirrel: 5 meters/second, 18 kilometers/hour
• Pig: 5 meters/second, 18 kilometers/hour
• Chicken: 4 meters/second, 14 kilometers/hour
• Mouse: 3.6 meters/second, 13 kilometers/hour

Humans

• Humans can walk at about 1.4 meters sendirisendiri second, which is 5 kilometers per hour, and run at speeds of up to about 8.3 meters per second, which is about 30 kilometers sendirisendiri hour.

Examples of Different Velocities

Four-velocity

While the classical velocity is a vector in three dimensions, in special and general relativity velocity has an additional fourth dimension, to be represented in spacetime. This velocity is also referred to as four-velocity. The four-velocity of an object changes in direction, but the value is constant at the speed of light
c. It is defined as:

U = ∂x/∂τ

Here
x
represents the world line, a unique distance that the object has traveled, and
τ
is the proper time or the time between two events in the reference frame of the two events.

Group Velocity

Group velocity is measured for waves. It describes the combined shape of the waves’ amplitudes. It can be calculated by finding
∂ω/∂k, where k represents the angular wavenumber, which is the spatial frequency of the wave. It is usually measured in radians saban meter. The angular frequency of the wave, a scalar measure of the rate of rotation, is denoted by
ω. It is generally measured in radians masing-masing second.

Hypervelocity

Hypervelocity is the velocity that is faster than 3000 meters per second. Solids moving with hypervelocity behave similarly to fluids because the stresses due to the inertia are much higher than the strength of the material upon impact. When the hypervelocity is extreme, the two colliding objects turn to the gas state, becoming vaporized. Objects move with hypervelocity in space and it is a phenomenon that the spacecraft designers and astronauts need to consider because collisions at these speeds cause significant damage to parts or to the entire spacecraft. NASA has a hypervelocity impact testing facility, where they experiment with hypervelocity impacts between the orbital debris and spacecraft and spacesuit materials. The researchers accelerate small objects to velocities greater than 7500 meters saban second to test their impact on shields, spacecraft, and spacesuits.

References