Constant Velocity Car (Tumble Buggy)

Specs:

Size: 7" x 4"

Power Source: Two C Batteries (Sold Separately)

Frequently Asked Questions

What is the Constant Velocity Car?

The Constant Velocity Car, also called a tumble buggy, is a battery-powered car that travels in a straight line at a steady speed. It gives students a visible, repeatable source of uniform motion to measure, graph, and analyze, which is hard to produce any other way in a classroom.

What topics can I teach with it?

Uniform motion and constant velocity, position vs. time graphing and reading slope as velocity, speed comparisons and proportional reasoning, relative velocity, vectors and the independence of perpendicular motions, friction investigations, and uniform circular motion as an extension. The Representing Motion article and the Measuring Constant Velocity lab both use this car.

Does it come with batteries?

No. The car takes two C batteries, sold separately. Fresh batteries matter more here than in most equipment, since a fading battery slowly changes the car's speed and muddies student data.

How fast does it go, and can I change the speed?

The car runs at one steady speed, and students measure it rather than look it up. You can also run it at a second, slower speed: cover one of the C batteries in a layer of aluminum foil, and use it in place of one battery. Having two speeds available is what makes speed comparisons and chase problems possible with a single class set.

What surfaces does it run on?

Smooth, flat floors and long lab tables work best. Hallway tile is the classroom favorite because it gives students enough run length for several timing intervals. Carpet and rough surfaces slow the car and break the constant-speed assumption, though that makes a useful comparison when you move into friction investigations.

How many cars do I need for a class?

Plan on one car per lab group, so six to eight covers most sections. Two cars per group opens up relative velocity work: two cars moving toward each other, or a faster car catching a slower one, which is where the graphs start doing real work.

What grade levels or courses is this best for?

Middle school through AP and Honors physics, plus introductory college labs. Middle school students measure distance and time and calculate speed. High school students build position vs. time graphs, extract velocity from slope, and write equations of motion. AP students use it as the control case for comparing constant velocity against accelerated motion.

What else do I need to run the lab?

A meter stick or tape measure, a stopwatch, and masking tape to mark positions. For more precise data, pair the car with a BeeSpi V photogate, an Electronic Spark Timer, or a PocketLab Voyager 2 riding on the car itself.

How do students produce a position vs. time graph?

Mark the floor at fixed time intervals as the car passes, or mark fixed distances and time each one. Either way students plot position against time and get a straight line whose slope is the car's velocity. Because the motion really is uniform, the points fall close to the line, so students can focus on interpreting slope instead of explaining away scatter.

Can I use two cars for relative velocity problems?

Yes, and it is one of the strongest uses of the car. Run two cars at different speeds using the foil dummy battery trick, then have students predict where and when the faster car catches the slower one. They solve it algebraically or graphically first, then mark the floor with their prediction and watch it play out. See Fresh Ideas for Your Relative Speed Discussions for setups.

How is this different from the Acceleration Car?

The Acceleration Car is a pull-back car that speeds up and then slows down, so it models changing velocity. This car holds a steady speed. Running both gives students a direct contrast between a straight-line position graph and a curved one, which is usually the moment the difference between velocity and acceleration lands.

Does it include instructions?

Yes. The Instructional Guide lays out a series of investigations, from basic speed measurement through friction and circular motion extensions. The Hands-On Kinematics page adds classroom-ready graphing activities.