The Atwood's Machine Lab

Here's yet another lab that we did to learn more about how the world works around us, called the Atwood's Machine.  In this we put a string through a pulley with attachments on either end to add weights to.  By using this system and adding certain weights on each side we were able to do a lab where we could keep the total force the same and just add to the mass of the system and find the acceleration.  This means that if there is a 0.5 kg difference in mass with the 2 sides that would make a difference of 5 newtons of force, and we could add the same mass to both sides and keep the unbalanced force 5 newtons.  However, even if the force was the same, adding the extra mass changed the acceleration when we let go and the heavier block fell to the floor and the lighter one went up.  For our first lab we did this a few times keeping the force the same and the total mass was our independent variable while the acceleration was the dependent variable changing depending on the mass.  The equation we ended up with for this was a = 0.046/mass.

We did a second lab using the same system, but instead of changing the mass and keeping for force the same, we actually kept the total mass the same and changed the net force.  To do this, we started with the 2 weights on either end of the string with a bigger difference in mass, but changed both of them by the same amount bringing them closer and closer together.  This diminished the total force, while keeping the same mass in the system.  Our final equation we got was a = 14.9 (Fnet) + 0.2, but the 0.2 was so small at the end it could just be taken out due to error.  The picture on the right shows this lab's data on the right side of the board and the first lab's on the left side.

When looking at both these labs we looked at patterns and noticed the equation of the first lab (a = 0.046/mass) the constant, 0.046, was very close to our unbalanced force of 0.05 which never changed throughout this lab.  If this was true, that equation would relate to a = Fnet/mass, so we took that and checked it with the second lab.  In this lab the mass was always .05, and force divided by that is the same thing as multiplying by 20, not far off from our 14.9.  When comparing with other groups they had similar results and we came up with the consensus that acceleration is in fact equal to the total force divided by the total mass in the system.  To learn more please check out my video about the forces behind the Atwood's Machine at https://www.youtube.com/watch?v=pPF2Z6yaU8s.  Thanks and I'll see you soon in my next blog, the Modified Atwood's Machine where we learn about tension in the string.