In sports such as athletics (or swimming, …), the gold medal is awarded to the person who finishes first, ie the person who reaches the finish line in the shortest time, and we call that movement the fast runner. the fastest (or the fastest swimmer).

You are watching: What is Velocity?

*So what is the quantity to know how fast or slow the motion is? that is speed. In this article, we will learn in detail what speed is? How are the formulas for speed and the units of velocity written?*

**I. What is velocity?**

– Velocity is the distance traveled in a unit of time

– Velocity magnitude indicates how fast and slow the motion is and is calculated as the distance traveled in a unit of time.

**II. Speed calculation formula**

Speed is calculated by the formula:

– In there:

v: Velocity of the object.

s: Distance traveled by the object

t: Time goes all the way

**III. Unit of speed**

– The unit of velocity depends on the unit of length and the unit of time

– Legal unit m/s; km/h

1m/s = 3.6km/h; 1km/h = 0.28m/s.

– The magnitude of the velocity is measured by the tachometer

* * Question C5 page 9 Physics textbook 8:* a) The speed of a car is 36 km/h, that of a cyclist is 10.8 km/h of a train is 10 m/s. What does that indicate?

b) Which of the three movements above is the fastest and the slowest?

**° Solution:**

a) – The speed of a car is 36 km/h. In one hour, the car travels 36 km.

– The speed of a cyclist is 10.8 km/h indicating that in one hour, the cyclist travels 10.8 km.

– The speed of a train is 10m/s: in one second, the train travels 10m.

b) To compare the motions, the velocities of the movements must be compared to the same unit.

– The speed of the car is: v1 = 36 km/h = 36000m/3600s = 10 m/s

– The speed of the bicycle is: v2 = 10.8 km/h = 10800m/3600s = 3m/s

The speed of the train is 10m/s.

→ So the train is the fastest, the cyclist is the slowest.

* * Question C6 page 10 Physics textbook 8:* A train in 1.5 hours travels a distance of 81 km. Calculate the speed of the train in km/h, m/s.

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**° Solution:**

The speed of the train in km/h is:

– Convert s = 81(km) = 81000(m), t = 1.5 hours = 1.5.3600 = 5400(s)

⇒ The speed of the train in m/s is:

* * Question C7, page 10, Physics textbook 8: *A cyclist rides a bicycle for 40 minutes at a speed of 12 km/h. What is the distance traveled?

**° Solution:**

– We have: 40 minutes = 2/3 hours

– From the formula for calculating the speed:

⇒ The distance traveled by the person is:

– Answer: s = 8(km).

* * Question C8 page 10 of Physics textbook 8: *A person walks at a speed of 4 km/h. Find the distance from home to work knowing the time it takes the person to get from home to work is 30 minutes.

**° Solution:**

– We have: 30 minutes = 0.5 hours.

– The distance from home to work is equal to the distance that person has traveled in 30 minutes.

⇒ The distance that person has to travel is: s = vt = 4,0.5 = 2 (km).

So, for this lesson, you need to remember the formula for calculating speed is v = s/t from which you can deduce the formula for calculating the distance s = vt and the formula for calculating time t = s/v. At the same time, you should also note that the unit of legal speed is m/s or km/h.

*—You may be interested:*

In addition, in navigation, people also use “button” as a unit of speed measurement. The node is the speed of a movement traveling 1 knot per hour. Knowing the length of 1 nautical mile is 1,852km, we can easily calculate the node to km/h: 1 node = 1,852 km/h = 0.514m/s.

The speed of light is 300 000 km/s (3,108 m/s). In the universe, the distances between celestial bodies are very large, so in astronomy people often express those distances by “light years. A light year is the distance light travels in a year.

In astronomy, people take a light year as 1016 meters (10 million billion meters). Yet the distance from Earth to the near star (near- **Proxima Centauri)** up to nearly 4.3 light-years.

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So, with the content of the lesson, did you understand what speed is? Memorize formulas and units of velocity and apply in solving exercises. These concepts will accompany us throughout the content of physics, so you need to remember them well, good luck with your studies.

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