Speed

Measurement is a key concept in science. We measure various quantities using base or fundamental physical units. Speed is one of these quantities. It calculates how far an object travels over a certain period. This session will focus on understanding speed in more detail, including its physics and units.

What is Speed? – Definition

Speed is defined as the rate at which an object covers distance. It measures how quickly something is moving from one place to another, typically expressed in meters per second (m/s) or kilometers per hour (km/h).

Speed Formula and Symbol

Speed is a fundamental concept in physics, represented by the symbol v. The formula to calculate speed is:

v = d/t​

Where:

• v is the speed,
• d is the distance traveled,
• t is the time taken to travel that distance.

How to measure the Speed

1. Determine the Distance: First, measure the distance the object has traveled. This can be done using a meter stick, a measuring tape, or other suitable measuring tools, depending on the length required.
2. Record the Time: Use a stopwatch to measure the time it takes for the object to travel the measured distance from start to finish.
3. Calculate Speed: Apply the speed formula: v=td​ where v is the speed, d is the distance, and t is the time. This calculation will give you the speed in units like meters per second (m/s) if you measure distance in meters and time in seconds.
4. Repeat Measurements: For accuracy, repeat the measurement several times and calculate the average speed.

Speed Unit

• SI Unit: Meters per second (m/s)
• CGS Unit: Centimeters per second (cm/s)

Examples of Speed

1. A Car on the Highway: A car traveling at a speed of 60 miles per hour (mph) on the highway.
2. A Jogger in the Park: A jogger running at a speed of 6 kilometers per hour (km/h) in a local park.
3. A River Current: A river flowing at a speed of 2 meters per second (m/s).
4. A Bicycle in a Race: A cyclist racing at a speed of 25 km/h in a cycling competition.
5. An Airplane: An airplane cruising at a speed of 500 mph at altitude.
6. A Conveyor Belt: A factory conveyor belt moving at a speed of 1 meter per second.
7. Earth Rotating: Earth rotates at an equatorial speed of about 1,670 km/h.
8. A Bullet Train: A high-speed bullet train traveling at 300 km/h.
9. Wind Speed: Wind blowing at a speed of 15 m/s during a storm.
10. A Spacecraft: A spacecraft traveling at about 28,000 km/h in orbit around Earth.

Types of Speed

1. Average Speed

Average speed is calculated by dividing the total distance traveled by the total time taken to travel that distance. It is a useful measurement when assessing the overall rate of travel over a journey that may include varying speeds. For example, if you drive 100 kilometers in 2 hours, including stops and starts, your average speed is 50 kilometers per hour.

2. Instantaneous Speed

Instantaneous speed measures the speed of an object at a specific instant. It is often recorded using speedometers in vehicles, which show the speed at any given moment. This type of speed is crucial for understanding dynamic conditions, such as a car’s speed as it maneuvers around a curve or when adjusting for road conditions.

3. Constant Speed

Constant speed occurs when an object moves at a steady rate with no changes in velocity — no acceleration or deceleration. An example of constant speed is a clock’s second hand which moves at a consistent pace around the clock face. Constant speed is rare in everyday situations because external factors often cause speed to vary.

4. Variable Speed

Variable speed describes an object whose speed changes over time. This can involve acceleration (speeding up) or deceleration (slowing down). Variable speed is commonly seen in vehicles navigating through traffic or during athletic activities, like running a race where speed may vary dramatically based on the racer’s strategy and endurance.

5. Relative Speed

Relative speed considers the speed of one object in relation to another. It is particularly relevant when objects are moving in different directions or at different speeds. For example, if two trains move towards each other, each at a speed of 60 km/h, their relative speed is the sum of their speeds, which is 120 km/h. This concept is critical in scenarios like avoiding collisions or in sports where players move towards or away from each other.

6. Angular Speed

Angular speed is used in scenarios involving rotational motion and describes how quickly an object spins around an axis. It’s typically expressed in radians per second or revolutions per minute. Angular speed is crucial in engineering applications involving gears, turbines, and engines, as well as in observing celestial objects in astronomy. For example, the angular speed of Earth’s rotation can be described as about 0.0000727 radians per second, equating to approximately 360 degrees per 24 hours (a full rotation each day).

FAQs

What is speed and its unit?

Speed measures how fast an object moves. The SI unit of speed is meters per second (m/s).

What is speed and velocity?

Speed is a scalar quantity indicating how fast an object moves, while velocity is a vector, including direction and magnitude.

What is the speed short answer?

Speed is the rate at which an object covers distance.

What is speed equal to?

Speed equals the distance traveled divided by the time it takes (speed = distance/time).

Is velocity speed in physics?

In physics, velocity refers to speed with a direction, making it a vector quantity, whereas speed is scalar.