Measuring the Speed of an Object: Physics Lab

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• 0:01 What Is Speed?
• 0:39 Physics Lab Steps
• 3:00 Lesson Summary

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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this video, you will be able to explain what the speed of an object is and how to calculate it in real life situations. A short quiz will follow.

What is Speed?

Speed is the rate at which an object's position changes, measured in meters per second. For example, if an object starts at the origin, and then moves three meters in three seconds, its speed is one meter per second. The equation for speed is simple: distance divided by time. You take the distance traveled (for example 3 meters), and divide it by the time (three seconds) to get the speed (one meter per second).

But what practical considerations do you have to make to measure an object's speed in real life? Time to do an investigation!

Physics Lab Steps

For this physics lab, you will need:

• A baseball or other small ball
• A constant-velocity car (or any battery powered motorized car that keeps going by itself)
• A stopwatch
• A tape measure or ruler
• Duct tape

Step 1: Place the constant velocity car in position on a surface, with plenty of space in front of it. Use the duct tape to mark the starting position of the car, placing a piece right behind the back wheels.

Step 2: Measure a distance from the tape, a few meters along the floor (longer is better), and place a second piece of duct tape. Note down the total distance.

Step 3: Turn on the motorized car, place it in position in front of the starting tape, and release it, starting the stopwatch at the same time.

Step 4: Stop the stopwatch when it reaches the second piece of tape, and note down the time in a data table that looks something like this:

Step 5: Repeat the experiment at least five times, and note down all the trials.

Step 6: Find the average of your five or more trials by adding up the numbers and dividing by how many trials you did.

Step 7: Calculate the speed of your car using the equation: speed equals distance divided by time.

And that's it; you've measured the speed of the car. To make this as accurate as possible, you should try to get to the second piece of tape before the car does - eye-line is important for accurate measurements. Whenever you measure anything, your eye should be directly above or next to the thing you're looking at.

Now we can try to do the same thing with the baseball, by dropping it from a height.

So Step 8: Measure a height along a wall or table leg, and mark it with a piece of duct tape.

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