SMART Carts in AP Physics 1

In AP Physics 1, students use the PASCO SMART carts to study motion, forces, momentum, and energy.  The carts have built-in sensors which can measure position, velocity, acceleration, and force; all of which is transmitted to the students’ laptops in real time.  This allows students to see how the changes in the physical motion of the carts produce the changes in data on the computer screen.  By observing these changes in real time, students make solid connections between visual observations and quantitative data.  In the picture below, students accelerate the cart by tying a string to the force sensor, the other end of which is attached to a mass which hangs over a pulley.  The students see how the velocity of the cart changes as it speeds up.  By varying the mass of the cart or the mass tied to the other end of the string, students derive the relationship between acceleration, force, and mass (Newton’s 2nd Law of Motion) from their own data.

Velocity exploration while varying mass

The carts also allow students to measure quantities that are difficult to measure otherwise.  The picture below students connecting two of the carts together, which are then connected to a third mass which hangs over a pulley.  This allows the students to observe the forces between the two carts as they acceleration, discovering that the force on one cart is always the same as the force on the other (Newton’s 3rd Law of Motion).  These measurements have not been possible for high school students in the past.  

Exploration of Newton's 3rd Law

In the picture below, students use the carts’ force sensor to study the effects of cushioning during a collision.  The carts roll down a track and collide with an object at the bottom.  Because this collision happens very quickly, with a time frame of a few hundredths of a second, the force on the cart can’t be measured with typical lab equipment.  The carts force sensor can measure forces over these small times, allowing students to clearly see the differences between crashing into a block of wood versus a block of foam.  They also derive that the impulse on the cart (force multiplied by time) is equal to the change in momentum of the cart by finding the area under the graph, a mathematical technique they will learn in calculus.  

Impulse exploration

An example of the data collected is shown below.  Students see that the force is much less for the soft collision, but that the impulse is the same for both.

Impulse data from collision with block of wood and with foam

The most powerful aspect of using the SMART carts is their versatility and ease of student use.  By using the carts many times throughout the year for a variety of different labs, students build an understanding of how to set up data collection and how to interpret the data.  The first time they use them, they require step by step instructions from the teacher.  By the end of the first semester, they can design a lab completely on their own.  This includes deciding the question or problem to be studied, the data to be collected, setting up the software and the carts for data collection, and interpreting and analyzing the data, applying other mathematical techniques as needed.  The students in the picture below designed a lab to show why car collisions are designed to be inelastic (cars stick together) rather than elastic (cars bounce apart after colliding).  This would not be possible if the students were not intimately familiar with the carts and the software.

Exploration of elastic and inelastic collisions

Written by Dan Marek
AP Physics Teacher at Grapevine High School