1. Understanding Speed
Speed tells us how fast an object is moving. It shows how much distance an object covers in a certain amount of time.
If an object covers more distance in less time, it is said to be moving faster.
1.1. Speed as a Measure of Fastness
When you compare two vehicles and say, “This one is faster,” you are actually comparing their speeds. Speed gives a simple number to describe this idea of fastness.
1.2. Scalar Nature of Speed
Speed is a scalar quantity, which means it has only magnitude. It does not tell us anything about direction.
2. Formula for Speed
Speed can be calculated using a simple formula:
\( \text{Speed} = \dfrac{\text{Distance}}{\text{Time}} \)
This formula tells us that speed increases if distance increases and decreases if time increases.
2.1. Example of Calculating Speed
If you travel 100 meters in 20 seconds, your speed is:
\( \dfrac{100}{20} = 5 \, \text{m/s} \)
2.2. Units of Speed
Common units include:
- meters per second (m/s)
- kilometers per hour (km/h)
Vehicles usually use km/h, while scientific measurements often use m/s.
3. Types of Speed
Speed may not always be constant. Sometimes an object moves steadily, and sometimes its speed keeps changing.
3.1. Constant (Uniform) Speed
If an object covers equal distances in equal intervals of time, its speed is constant.
3.2. Variable (Non-Uniform) Speed
If the distance covered in equal time intervals keeps changing, the speed is not constant. This happens often in real life, like in city traffic.
4. Speed in Everyday Life
We frequently use the idea of speed without even noticing it. When a cyclist moves faster than a walker, or when a car overtakes a bike, we are comparing speeds.
4.1. Comparing Speeds
If two people start running at the same time, the one who covers more distance in the same time has the higher speed.
4.2. Instantaneous Speed (Informal Idea)
The speed shown on a speedometer at a particular moment is called instantaneous speed. It tells you how fast you are going right now.
5. Speed Cannot Be Negative
Speed only has magnitude. It cannot have direction, so it is never negative. Even if you move backward, the speed value will still be positive because distance is always positive.
5.1. Example
If you walk 5 meters backward in 2 seconds, your speed is:
\( \dfrac{5}{2} = 2.5 \, \text{m/s} \)
Even though you moved backward, speed remains positive.