DAY 25 LETS GO! TODAY AT A GLANCE: 1) You try a math example and learn about pulleys. 2) We look at pulleys in a different way. 3) LOTS of learning/graphing and questions for pulleys

LETS GET OUT THE HW We will have a HW turn in next class, possible HW are Day 23, Day 24, Day 25. Questions? So we have 1 more HW due for tomorrow.

TENSION AS A FORCE Tension is the force from a rope or string. A rope can only have 1 tension on it.

Put equal masses on each side Put equal masses on each side. Now draw a FBD for each mass under your general picture. .

Put unequal masses on each side Put unequal masses on each side. Now draw a FBD for each mass under your general picture. Remember to figure out which way the imbalance is! .

As one side gets more and more massive, what will happen to the acceleration? Is there a limit to the value? MY THINKING: “The weights oppose each other. As one gets heavier, its like the other weight is not really there. So its going be like its not opposed. Which would be free fall.

Lets Do An Example To Start Us Off Here is a massless pulley that rotates without friction. What does that mean? MAIN GOAL: What is the acceleration of these masses? SIDE GOAL: How much tension is there? 3 kg 7 kg

1st: Draw a FBD on each Circle forces, label imbalance/balanced Next: Lets CREATE net force equations for this situation.

Lets solve for our: Main Goal: Side Goal:

Now for a new, fresh look: Draw this in your notebook front and center. CALL IT: Pulley on table Observe the setup

IN CLASS NOTEBOOK The graph: The reasoning:

IN CLASS NOTEBOOK A) B) The reasoning:

IN CLASS NOTEBOOK The result: The reasoning:

IN CLASS NOTEBOOK The result: The reasoning:

1) What do you observe? 2) What can you measure? 3) What can you change?

GOALS: 1) Determine how the acceleration relates to the force making them move. 2) Determine how the acceleration relates to the total mass of the system (but not changing the hanging mass).

GOALS: 1) Determine how the acceleration relates to the force making them move. Get actual trials More hanging weight = more acceleration in a directly proportional amount 2) Determine how the acceleration relates to the total mass of the system (but not changing the hanging mass). Get actual trials More mass on top = less acceleration because more mass is being moved by the hanging thing.

LETS SHOW IT Assume no friction, and the pulley and rope are mass less (WHY?)

DRAW A FBD FOR EACH Hanging Mass Table Mass Write the imbalance/etc, circle, create a net force equation for each:

DO MORE Lets now solve for TENSION for each Hanging: Table And now set the Tensions equal to each other to solve for acceleration:

QUESTION: Try the 1st HW question for me. On the boards!

1) Any volunteers to tell me what they think? Possible Answers: Block B’s weight pulls it down. The imbalance is down, so the down pull MUST be larger than the up pull on B. The up pull is the tension, so it must be less. The amount of imbalance is the weight of B. That weight moves it and A. Since the tension is just moving A and NOT B, the tension is less than B’s weight.