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The Physics of Classic Pullback Cars

In 1978, a Japanese company called Takara made the most famous pullback car in the world. The Choro-Q, referred to as “Penny Racers” in the United States, consisted of squeezed images of a real car. It also had a coil-spring pullback motor. These cars quickly became collectibles due to their low price and availability of special edition models. The pullback car has a metal or plastic outer shell, which houses a chassis with the gear box, axles, and wheels. The axle and back wheels are attached to the gear box, which contains gears. When the user turns the wheels, the axle winds the gears in the gear box, making the car move.

Physics Background

It is important to understand the difference between velocity and acceleration, especially when working with pullback cars. An object accelerates when its velocity changes, but velocity is not just a measure of speed. It also takes direction into account. Acceleration is when an object’s direction of motion, speed, or both change. An object can accelerate if it is moving in a straight line with changing speed or if it is moving in a circle with variable or constant speed.

If you close your eyes while moving at a constant velocity, you cannot even tell that you are in motion. This is why amusement ride designers would never create rides that move with constant velocity. You can feel the acceleration of amusement rides, especially rides like roller coasters and swings. For those who love these rides, the faster speed and direction change, the better. Acceleration occurs due to the action of an unbalanced force on an object. This falls under Newton’s Second Law of Motion, which states that acceleration is in direct proportion to the unbalanced force. The acceleration is inversely proportional to the object’s mass. This makes sense when thinking about the mass of cars and the power of their engines. Two cars with the same mass will not accelerate the same if they have different engines. Tractor trailers take much longer to get up to the speed limit due to their sheer size.

Physics Activities with Pullback Cars

The pullback car is ideal for helping kids understand physics, as it is easy to use in a number of experiments. The net force of the car is produced by a spring, which winds as someone drags the car backward across a flat surface. Students can increase the inertia of the car by placing small objects in the car’s front seat; this allows them to see how mass and acceleration are related. During the first 1.5 meters of its motion, the car accelerates in a predictable manner. After this, the acceleration becomes negative, which may cause the car to veer off to the side. The following activities are just some of the many ways the pullback car can help teach students about physics.

Exploring with Cars

Sparking an interest in uniform and accelerated motion can be as easy as placing a few pullback cars on a desk or laboratory table before class begins. Students will naturally pick up the cars and start racing them, which can lead to curiosity about what makes the cars work.

Top Speed Determination

Students should develop an experiment to determine the top speed of a pullback car. One question that can accompany this laboratory activity is “Does the speed you measured represent an instantaneous or average speed?” This question often sparks discussion about determining the speed of a pullback car or other object. Some teachers use this experiment to introduce limits and the concept of the derivative.

Introducing Acceleration

After discussing the meaning of acceleration, students should work together to develop a procedure for measuring the acceleration of their pullback cars. After determining the acceleration, students should compare the acceleration of their cars with the acceleration of the other cars in the classroom.

Ticker Tape Timer Experiment

Teachers who have access to a ticker tape timer can help students study the details of the car’s acceleration. Students should use the tapes to determine if acceleration is constant the entire time the car is moving, or if the acceleration is only constant during a portion of the movement.

Automobile Research

Students should research the acceleration of pullback cars versus the acceleration of pullback cars. Provide auto magazines or access to the Internet so students can research this information. Hold an informal discussion about the results once each student has completed the assignment.

Mass and Acceleration

Give students small objects and instruct them to add mass to their cars. They will be able to observe that each car accelerates regardless of mass. They will also be able to observe that acceleration decreases when a car’s mass increases.

The following resources explain more about acceleration, velocity, and other physics concepts.

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Article by
Matt Robertson
Matt is the Managing Partner at Leland-West Insurance Brokers, Inc. He started with the firm while still a college student, way back in 1984. According to Matt his only remaining hobby is Motorsport ... because its all he can afford ("will work for tires"). Reach him at matt@lelandwest.com