IB Force Table Lab

This is an optional Lab - every person should do their very own calculations - but work in a group and help each other.  I will give you 5 points of lab extra credit if you submit your very own calculations.

• We have 6 round force tables in the back, and 12 sets of precision masses - Each group should grab one table, and two sets of masses.  There are also Jumbo Paper Clips that each have a mass of about one gram if you need them.  Please put your masses back the way they are when you pick them up, and use the metal handle to carry them, don't try to support them from the bottom, or they will fall all over.  These sets are expensive, so treat them with care - if you do drop them, find all the pieces and put them back together.

• There are two different labs you can do - either one unknown (VF9B) or two unknowns (VF9C - with matrices).  IMO the two unknowns is easier to do (even though it involves matrices) because you don't need to find an angle which students find confusing.  Pick one of these (or do both if you want)

• You will need to use the camera on your Satan Phone to submit your work.  This is not a license to then go on Satanic Social Media.

Here's what to do:

1. Pick two different mass amounts to put on the hangers.  In this picture I chose 200 grams and 150 grams.  Keep in mind that the hanger itself has a mass of 50 grams, so I put 100 + 50 on the one that has 200 grams, and just a 100 gram mass on the other.

2. Pick a couple angles like I did.  Put them in the same half of the circle to keep things easy.  In this example I put them in the same quarter of the circle, but I could have put the 200 gram in the upper left quadrant as well.  Loosen the thumbscrew, move the pulleys to the angles you picked, and tighten the thumbscrew so the pulley stays put.

3. Make a force diagram on your paper and use maths to calculate the components of the equilibrant Fx and Fy, and ultimately its magnitude, and the angle it makes with either x or y.  (In this example I found the angle with y)  Show your two equilibrium expressions like this: (Yours will be different...)

   1. X:   Fx + 200sin(10) + 150cos(25) = 0

   2. Y:   Fy + 200cos(10) + 150sin(25) = 0

4. And draw a picture of the equilibrant, labeling the magnitude (hypotenuse) and some angle.

5. Put the third pulley at the angle you calculated, and put a mass equal to its magnitude on the end of the string (keeping in mind that the hanger already has a mass of 50 grams).  If you need a mass smaller than 5 grams, use Jumbo Paper Clips - they each have a mass of about 1 gram.

6. Shift the strings around on the keyring in the middle so they come off it 90o from the ring itself

7. If it works, and you did it right, the ring will stay off the post in the middle, so use your Satan Phone to take a picture of your group saying Ta Daa! and holding your hands in a celebratory pose.  (There are some examples in the linked document - replace those with your own photo)

8. Take a photo of your very own work on your very own paper, and put that in the first part of the linked document. 

Here's what to do:

1. Put a known mass (not too big - 200-500 grams) on a pulley that is straight toward you.  In this picture I put 200 grams at 0o.

2. Put the other two pulleys at two different angles.  To make it easy, pick angles like I did that are in the other half of the circle, so it's like the problems we solve.  Here I picked 23 degrees on the left side, and 55 degrees on the right side.  (Pick your very own angles)

3. Make a force diagram on your paper and use maths (matrices??) to calculate the values of A and B.  Be sure to show me the equilibrium expressions.  For my setup, the expressions would be:  (Yours will be uniquely different ; - )

   1. X:   -Acos(23) + Bcos(55) = 0

   2. Y:      Asin(23) + Bsin(55) - 200 = 0

4. Place the appropriate mass on A and B that you calculated.  You can use Jumbo Paper Clips as one gram masses if you need to.  Keep in mind that the hangers themselves have a mass of 50 grams.

5. Shift the strings around on the keyring in the middle so they come off it 90o from the ring itself

6. If it works, and you did it right, the ring will stay off the post in the middle, so use your Satan Phone to take a picture of your group saying Ta Daa! and holding your hands in a celebratory pose.  (There are some examples in the linked document - replace those with your own photo)

7. Take a photo of your very own work on your very own paper, and put that in the first part of the linked document.