Coffe Filter Terminal Velocity (Drag Lab)

Before this lab, we gathered as a class to discuss important ideas, and after our teacher's very important story of when he went skydiving with the jumpmaster and learning complex techniques like "the bellybutton banana" we went on to our normal routine of testing ideas through a lab.  We talked about how in skydiving the person accelerates down for a period of time, but after a while they stop accelerating and keep a constant, terminal velocity, but what makes this happen?  Well we know that if there is no acceleration, then all forces must be balanced, so what is counteracting the force on the earth pulling the skydiver downward.  As a class, we came to the consensus that it is air resistance creating a force strong enough to push up with as great of a force as is pushing down on the skydiver.  We wanted to learn more about the air resistance, yet without a plane we were stuck, so we decided to take coffee filters that we could measure the surface area and mass to test what the terminal velocity is.



We did two labs, one where we kept the mass the same but changed the surface area, and the other where we changed the mass but not the surface area.  When we kept mass constant we needed to start with 6 coffee filters stacked up and taped together, then used a motion sensor to find the terminal velocity, but changed the surface area by then making 2 stacks of 3 coffee filters and taping together (with the same amount of tape to keep the mass constant) then 3 stacks of 2 and finally 1 stack of 6.  We recorded our data and moved on, and with our second lab we just used one stack but added mass by merely stacking more and more coffee filters on.

Using what we learned from this lab and our previous knowledge, we decided that adding mass makes the terminal velocity higher, which makes sense as a higher mass would then mean a higher force of the earth on the object and to balance that force, the velocity must be higher.  However, we also found that surface area was inversely related to terminal velocity, so as it grew, the terminal velocity shrunk.  This also makes sense as why when parachutes shoot out they slow skydivers down by adding surface area.  With this in mind we realized when air resistance is added, not all objects fall at the same rate, only if they have a proportionate mass and surface area.  To learn more about terminal velocity, visit this video: https://www.youtube.com/watch?v=x4_dFDEpAaI and see how we found the terminal velocity of a ball without dropping it.  Thanks and I'll see you next time, probably a couple days before our third quarter ends and grades are due.

Modified Atwood Machine Lab

Welcome back, for the Modified Atwood's Machine Lab.  If you don't know about the regular Atwood's Machine or my lab my group and I did please visit http://tylerphysicsrules.blogspot.com/2016/01/the-atwoods-machine-lab.html.  This lab is very similar, except one of the suspended sides of the string we attached to a cart at the same level as a pulley to act as extra weight without adding force to the system and without adding friction so we could find an equation for the tension of the string.  We did two labs again with this new set up, one to where we change the mass and keep the force the same, and one where we change the force while keeping the mass the same.

To do the first lab, we just added mass on top of the cart to change the mass, but did not add any to the part of the string suspended in the air and therefor added no additional forces to the system.  As the mass increases we saw an inverse relationship with acceleration which fit our equation we got from the last lab, a=Fnet/mass.  As for the second lab, to change the force we added mass to the string suspended in air while taking the same amount of mass off the cart, so the mass of the system stayed the same while the force increased.  With the data gathered from this situation, we got another equation of a = 1.565 (Fnet), staying true to our a=Fnet/mass.

After doing these labs we went on to try and find tension during our Atwood Machine labs.  Our teacher gave us the equations a=(m1g-T)/m1 and a=(T-m2g)/m2, m1 being the mass of the heavier block or in the Modified Atwood's Machine it is the mass of the the only block, while m2 is only in the original lab and is the lighter block.  Using this and the original a=Fnet/mass equation, we can find tension in order to create a more accurate force diagram for each block.  To learn more in depth about these please visit my video at https://www.youtube.com/watch?v=EGy48BedMr0 where I explain the force diagram of a Modified Atwood's Machine.  Thanks, and I'll see you next time, likely my last time for at least a couple of months where I describe the physics behind coffee filters.

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.

Back at it Again in Physics (Ramp Angle and Acceleration Lab)

Well, it's the end of the quarter and midterms are next week, so I guess it means it's that time again to start cranking out these blogs.  To do this, we have to go all the way back to November 5th when we did the Ramp Angle vs. Acceleration Lab.  This lab was to see that if an object was placed on a ramp with no friction, how would the acceleration change in comparison to the angle of the ramp.  Based on what we know and that the fastest would be 90 degrees (free fall) and the slowest was 0 degrees (stationary), we made a hypothesis saying it was linear.  However, this lab was different from most because soon after we realized, what if the angle is increased over 90 degrees, them the acceleration starts to go back down.  We had to do the lab to find the right equation to compare the two variables, so to do so we downloaded an app on our phone to find the level of the ramp, and we used carts to simulate an object with no friction.  We also used motion sensors to gather the data for what the acceleration was at different levels.  Below is the picture of our group hard at work gathering data during this lab.

As we worked through it we figured we were right with what we thought would happen.  As the angle rose from 0 degrees to 90 degrees, so did the acceleration, however it wasn't quite linear, but at the same time it wasn't quite quadratic or a square root graph either.  We didn't know what to do with the data until our teacher came by and explained the situation to us.  We actually had to insert a sin graph in with the data to fit our points which is something we haven't seen in a physics lab before, yet it made sense as when the angle gets above 90 degrees a sin graph would also start a downward trend until it gets to the stationary 180 degrees.  After having this epiphany we put all the data on a whiteboard and got our equation to discuss what we learned with the rest of the class.

Our final numbers showed the equation that acceleration was equal to 10 x sin (0.0159 x degrees).  In addition to this we tried to find where the 0.0159 comes from and it turns out it is close to pi divided by 180 which converts from radians to degrees on the computer.  With that and the 10 being the acceleration of force of the earth on the object (g), the final equation is a = g x sin(θ).  To learn more, you can see a video I made about the forces acting on an object at rest on an inclined plane and accelerating down on an inclined plane at https://www.youtube.com/watch?v=mte2JCFTht0.  Thanks for visiting, and until next time... in about 20 minutes.