Today we investigated how mass and force affect acceleration. We used the air track, attaching a string from the glider, across a pulley on the end of the track, to a small basket hanging off the end of the table. The weight of the basket will be the constant force pulling on the glider and causing a constant acceleration. The recording of data and analysis was very similar to last week – we used Video Physics and Graphical Analysis apps, but they had to run through the process many times. The students took data for three different forces pulling on the cart and found the acceleration each time by finding the slope of the linear velocity vs time graph (see photo above).
They also took data for three different cart masses – you can add weights to the cart to increase its mass. The acceleration of the cart changed as expected, when pulling with a great force, the acceleration increased. If the mass of the cart was greater but the force was the same, then the acceleration decreased. So we can conclude that our data supports Newton’s 2nd Law, F = ma.
We had to be very careful with units in this lab. The students have to set an origin and scale in the Video Physics app and if they did it in centimeters (cm), they had to either write their acceleration is cm/s2 or convert to m/s2. We were adding masses labeled in grams to the bucket to change the force, but had to convert those to kg so we could calculate the force in Newtons (kg m/s2). This experiment can also be done with a simple cart with wheels and a pulley attached to the edge of a table. I encouraged the students to sketch the apparatus in their lab books, unfortunately I forgot to take a picture.