1. Bellwork
A truck is applying a 5000 N force to the right, a car 3000 N to the left. If the truck weighs 2000kg and the car 1500kg and are chained together, what rate will the whole system be accelerating at?

2. Atwood Machine Lab

3. Your tasks:
You will be given a pulley to make an Attwood machine out of.
You will have 2 tasks:
Predict the amount time it will take for one of your weights to be displaced 50 cm.
Place weights on your Attwood machine to make it travel 50 cm in a given amount of time (between 1 and 5 seconds)

4. This is a Performance Based Lab
You will get your times 15 minutes into class on Wednesday
A performance based lab is where you are given a task and are given points on how you do. In this lab…
12/10 for 5 or lower percent error
10/10 for 10 percent error
8/10 for 15 percent error… and so forth

5. Rules, Guidelines, and tips
Any and all resources you can find are fair game
If your are using an Atwood machine you have a 5 minute window. Make your prediction then grab the Atwood.

6. Rules, Guidelines, and tips
I have a photogate in the room for exact measurements of time.
Yes you have a week to work on this but it will take ALL of your time
If you are on your phone it needs to be on task or I will take the phone.
BE ON TASK

7. Rules, Guidelines, and tips
Assign Jobs:
Captain: Keeps everyone on task.
Takes care of logistics.
Math dude/chick: the one with the whiteboard
head up derivation of equations (whiteboards are great)
Recorder: the one with the paper
write down what you’re doing/ come up with mock times and accelerations to test yourself with
Nay sayer: The one who asks thoughtful questions.
look at things critically, frequently ask “why”
There's a big difference between being a dirt bag and being helpful. Don’t be the wrong one

8. A good starting place…
Create a formula which mathematically describes the situation. (use kinematic equations to find time when you have acceleration)
Create a prediction
Test that prediction. If it works, great, if not try and figure out why.
Did you account for friction/ did you need to….
Did you mess up your math…

9. How are your predictions going?
Bellwork
Sit with your lab group.
How are your predictions going?
Do they work with large mass differences?
What about small mass differences?
Why might that be the case

10. Friction
Find friction (from contact) by multiplying the normal force by a factor between 0 & 1 (this factor is written as “µ”)
Friction always exists, but it is sometimes negligible.
The longer something is in motion the more friction matters.
If the difference between actual and calculated gets bigger as time increases you need to include friction in your math

11. Using friction…
Your currently have … A=(g*m1-g*m2)/(m1+ m2) On top you have forces (g, an acceleration times mass= force) On the bottom you have masses. Friction is a force so it goes on the top… Friction normally slows things down so be sure to take that into account

12. Example problems
2 masses are tied together in an Atwood machine. If one mass is .5 kg and the other is .75kg what is the acceleration of the weights if the coefficient of friction is .1
In the above problem what is the smallest coefficient of friction that would prevent the system from moving? (no acceleration happens when the net force = what)

13. The second challenge… Find two weights which pass .5 m in a given time
Friction matters here too!!!
Don’t forget to do this one…
In order to solve…
Find the required acceleration
assign one weight
solve for the other one.

14. This is your second and last work day.
If you are ready to practice I will have numbers for you to practice on.