Speed is a familiar quantity in life, in sports such as racing, athletics, swimming… So what is speed? What is the exact formula for calculating speed, distance and time? The article below will help you better understand this quantity, thereby applying it in work and life.
What is velocity?
- Velocity is a quantity used to describe how fast or slow a movement is.
- The units of speed km/h, m/s, km/s… depend on the units of distance and time being considered.
Uniform straight motion
Formula to calculate velocity
In uniform straight motion, the velocity will be calculated according to the formula:
In it we have:
- v is the velocity
- s is the distance traveled
- t is the time the object moves
Formula to calculate distance
Applying the formula for calculating speed, we can easily calculate two quantities: distance and time.
When we know the speed and time, we have the formula to calculate distance:
Time calculation formula
When we know the speed and distance, we have the formula to calculate time:
The time an object travels is equal to the ratio between the distance traveled and the object's speed during that time:
In there:
- t: time the object travels (s or hours)
- s: distance traveled by object (m or km)
- v: velocity of an object moving uniformly along the distance (m/s or km/h)
- vtb: average speed of object over distance m/s or km/h)
Problem on calculating velocity in uniform motion
Lesson 1: Distance AB is 135 km long. The car goes from A to B in 2 hours and 30 minutes. Calculate the speed of the car, knowing that the car will rest for 15 minutes along the way.
Instruct
The time taken by the car to travel the distance AB (not including rest time) is:
2 hours 30 minutes – 15 minutes = 2 hours 15 minutes
Conversion: 2 hours 15 minutes = 2.25 hours
The speed of the car is:
135 : 2.25 = 60 (km/h)
Lesson 2: On the same distance of 24 km, the car takes the remaining 24 minutes and the motorbike takes the remaining 36 minutes. Which car's speed is greater and how many km/h?
Instruct
Conversion: 24 minutes = 0.4 hours; 36 minutes = 0.6 hours
The speed of the car is:
24 : 0.4 = 60 (km/h)
The speed of the motorbike is:
24 : 0.6 = 40 (km/h)
The speed of the car is greater than the speed of the motorbike and is greater than:
60 – 40 = 20 (km/hour)
Lesson 3: A car leaves A at 12:15 a.m. and arrives at B at 5:35 p.m. Along the way, the car rested for 1 hour and 5 minutes. Calculate the speed of the car, given that the distance AB is 170 km long.
Prize:
The time the car leaves and stops is:
5:35 p.m. – 12:15 p.m. = 5:20 p.m
Travel time by car is:
5 hours 20 minutes – 1 hour 5 minutes = 4 hours 15 minutes nice 4.25 hours
The speed of the car is:
170 : 4.25 = 40 (km/h)
Straight movement
a. Displacement
Displacement is determined by the change in coordinates of the object.
Note:
- In general, displacement is a vector quantity
has the origin at the initial position, direction from the initial position to the final position, the magnitude is equal to the distance between the initial position and the final position.
- Displacement is a quantity that can take on a positive, negative or zero value. While the distance traveled is a non-negative quantity.
b. Speed
- Velocity will be determined based on displacement per unit of time.
- Velocity is expressed in vectors, the vector direction displayed is the direction of motion. The length of the vector will tell us how fast or slow the movement is.
Average speed is a vector quantity determined by the quotient between the displacement of an object and the time it takes for the object to make that displacement.
Save idea: Average speed is only equal to the magnitude of average velocity when an object moves straight without changing direction.
Considered over a very small period of time, the average velocity will become the instantaneous velocity. The magnitude of the instantaneous velocity is the instantaneous speed.
Save idea: Thus, instantaneous velocity is also a vector quantity has its origin at the position of the moving object, points in the direction of motion and has a length proportional to the magnitude of the instantaneous velocity according to a specified scale.
What is speed?
a. Average speed
– A quantity that characterizes a property fast, slow of movement is speed.
If during a period of time the object moves a distance then:
The average speed of the object (symbol vtb) is determined by the quotient between the distance traveled by the object and the time it takes for the object to travel that distance.
– In the SI system, the unit of speed is m/s (meters per second). Some other commonly used units of speed are km/h (kilometers per hour), km/s (kilometers per second), etc.
b. Instant speed
- To consider the fast and slow motion of an object at each time, the speed must be considered in terms of speed very small period of time.
- Average speed calculated in a very small amount of time Instant speed Describes the speed or slowness of the movement at that time.
- When an object moves at a constant instantaneous speed, we say the object's motion is uniform motion. On the contrary, we say the motion of an object is irregular.
Difference between speed and velocity
Many people often confuse velocity and speed as 1. But in reality, these two quantities are completely different.
Basis for comparison | Speed | Speed |
---|---|---|
Meaning | Speed refers to the distance covered by an object in unit time. | Velocity refers to the displacement of an object in unit time. |
Identify | How fast is something moving? | In what direction is something moving? |
Great quantity | Directionless | Vector |
Point out | The quickness of the object. | Quick and location of objects. |
Proportion | Change distance | Shift change |
When the body returns to its original position | It won't be zero | It will be zero |
Moving object | The speed of a moving object can never be negative. | The velocity of a moving object can be positive, negative, or zero. |
Uniform linear motion
Because uniformly variable linear motion has velocity that changes uniformly over time, acceleration remains constant over time: constant.
Call v0 is the velocity at the initial time is the velocity at time t.
Because should