Understanding Speed in Softball and Everyday Life

Did you ever play softball? You may have found it easy to hit the large slow moving ball. Well that's only one kind of softball. Fast-pitch softball is a whole new game. The ball is not pitched slowly. Instead, its speeds are nearly as fast as a baseball. Female athletes can throw the ball at speeds of around 120 km/h. That’s about 75 mi/h. For a male athlete, the ball may travel even faster. The speed of the ball makes it very hard to hit. The batter barely has time to swing the bat.

In fast-pitch softball, the pitcher uses a "windmill" motion to throw the ball. This is a different technique than other softball pitches. It explains why the ball travels so fast.

Speed is one aspect of motion. It is a measure of how fast or slow something moves. To determine speed you must know two things. First, you must know how far something travels. Second, you need to know how long it takes to travel that far. Speed can be calculated using this formula:

A familiar example is the speed of a car. In the U.S., this is usually expressed in miles per hour (mph). Think about a trip you and your family made in the car. Maybe the trip covered 120 miles and it took 3 hours. What was the car’s speed?

The speed of a car may also be expressed in kilometers per hour (km/h). The SI unit for speed is meters per second (m/s). This is the unit of measure a scientist would use.

Speed limit signs like this one warn drivers to reduce their speed on dangerous roads.

When you travel by car, your speed may vary. In other words, you usually don’t move at a constant speed. You may go faster or slower. It may depend on the speed limits, traffic, and traffic lights. For example, you might travel 65 miles per hour on a highway. When going through a city, you may only be going 20 miles per hour. You might even have to stop at traffic lights. You slow down as you turn corners. You speed up to pass other cars. It's easy to figure out the average speed, but what about your speed at any moment?

The speed you are going at any given instant is called instantaneous speed. It may vary from moment to moment, and is hard to calculate. Fortunately, we have speedometers to tell us how fast we are going in a car at any moment. You may even have a speedometer on your bike.

Cars race by in a blur of motion on an open highway but crawl at a snail’s pace when they hit city traffic.

It's easy to figure out the average speed. The average speed is the total distance traveled divided by the total time it took to travel that distance. To calculate the average speed, you can use the general formula for speed that was given above. What if you took a 75-mile car trip with your family? Your instantaneous speed would vary throughout the trip. If the trip took a total of 1.5 hours, your average speed would be:

average speed = 75mi/1.5h = 50mi/ h

You Try It!

Problem: Terri rode her bike very slowly to the top of a big hill. Then she coasted back down the hill at a much faster speed. The distance from the bottom to the top of the hill is 3 kilometers. It took Terri 15 minutes to make the round trip. What was her average speed for the entire trip?

What is speed? How is it calculated?

Sam ran a 2000-meter race. He started at 9:00 AM and finished at 9:05 AM. He started out fast but slowed down toward the end. Calculate Sam’s average speed during the race.