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Pulleys

Pulleys. Vanderbilt Student Volunteers for Science Fall, 2010 Training Refresher. Important!. Please use this resource to reinforce your understanding of the lesson! Make sure you have read and understand the entire lesson prior to picking up the kit!

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Pulleys

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  1. Pulleys Vanderbilt Student Volunteers for Science Fall, 2010 Training Refresher

  2. Important! • Please use this resource to reinforce your understanding of the lesson! Make sure you have read and understand the entire lesson prior to picking up the kit! • We recommend that you work through the kit with your team prior to going into the classroom. • This presentation does not contain the entire lesson—only selected experiments that may be difficult to visualize and/or understand.

  3. Management Notes • Groups should have at least 4 students. • ALL VSVS volunteers need to know how to do this experiment. We highly encourage that you practice using the pulleys before teaching them! • VSVS members should each supervise one or two groups of students to ensure that the groups are following instructions and using materials properly to achieve appropriate results. • Write down balance readings from each group on the board (tabular form may be the easiest to use).

  4. I. Demo: Tug of War (pg. 3) • This introduces pulleys and the trade off between the distance an object moves and the amount of force needed to move an object. • Arrange the PVC pipes as shown on the right with the rope tied to one and wind the rope around the pipes. • Pick one of the smaller students to be the person that will pull the rope and have the student put on gloves (optional, but recommended).

  5. I. Demo: Tug of War (cont.) • Two VSVS volunteers, each holding a PVC pipe and pulling in opposite directions, try to separate the pipes. • At the same time, the student volunteer, standing along side of one of the VSVS volunteers and gripping the free end of the rope with both hands, pulls on the rope to attempt to draw the pipes together. • Unwind the rope until it is only around the pipes once. Then ask the student volunteer to try again (this time, the student will not be able to prevent the VSVS volunteers from separating the pipes).

  6. II. Intro to Pulleys (p. 4) • Refer to manual for more details. • What are the six classes of simple machines? • What are pulleys? • Simple machines that are used in different ways to lift objects. • They can change direction of a force and can make it easier to lift heavy objects. • Single, fixed, movable pulleys. • Demo all procedures in Parts III and IV so that students will understand what to do. One VSVS member should call out instructions for each activity.

  7. III. Examining Materials and Using a Spring Balance (pg. 5) • The pulley stands must be placed near the edge of a table. • Weights need to sit flat on the recessed end with the hook up.

  8. III. Examining Materials and Using a Spring Balance (cont.) • Have students examine the spring balance. • Show students how to adjust zero by pulling or pushing the metal tab at the top of the plastic casing. • Tell students that the metal tab marker should always start out even with the “0” mark. • Tell students they must “zero the balance” each time they measure. • Check to make sure student groups do this correctly.

  9. III. Examining Materials and Using a Spring Balance (cont.) • Have students hold the spring balance by the top metal ring. • Practice weighing the 200g weight by itself by hooking the spring balance to the hook on the weight and carefully raising the spring balance until the 200g weight is hanging freely. Keep arm still to get a good reading. • Record the reading of the weight in the Mass of Object (load) column on the Pulley data sheet. (If readings are significantly different from 200g, check the balance or the way the students are using it)

  10. IV. Single Fixed Pulley (pg. 6) • Hand out a set of pulley diagrams to each group. • Remind the students that it will take several group members to do each measurement—they will need to work together to manipulate and string the pulleys! • Make sure the pulley stands are near the edge of the table with the lettered side facing the students who will be stringing the pulley. • Have students follow the diagram for Single Fixed Pulley as a VSVS member gives the instructions.

  11. IV. Single Fixed Pulley (p. 6) • Place a single pulley on the middle ring (B) of the stand. • You may want to wind the strings of A and C around the pipe to prevent the strings from becoming tangled. • Take the short loose string off the straw. Thread the string through the top of the pulley (or between the pulley wheel and the metal bar surrounding it). Try to keep the string in the groove of the pulley. • Hook the paper clip to the weight. Let go of the string on the other side, but keep tension on the string by pulling down gently.

  12. IV. Single Fixed Pulley (cont.) • Take the spring balance, check the zero, and hold the balance upside down. • Hook the spring balance and pull the spring balance gently until the weight lifts off the platform. • The spring balance may need to be pulled below the level of the pulley stand as shown on the right. • Keep tension on the balance and take a reading. • Refer to the manual for discussion. • Dismantle the setup. Wind the string around the straw and put it back in the ziploc bag.

  13. V. Single Movable Pulley (pg. 8) • Unwind the short string already attached to ring A on the pulley stand. • Note: the pulley may twist around if the student is not holding it properly. Before a balance reading is taken, students should make sure that neither the pulley nor the string is twisted. • Hold the hook above the wheel on the single pulley and hook its bottom hook to the weight. One student should continue to hold the pulley until it is connected. • Thread the short string attached at “A” through the bottom of the pulley (from left to right), and slip it in the groove of the pulley. • Grasp the paper clip and hold it up toward the top of the stand. Make sure the string is in the groove of the pulley.

  14. V. Single Movable Pulley (cont.) • Hold the balance upright and check the zero. • Attach the spring balance to the paper clip that is being held up in the air. • Let go of the pulley and slowly raise the balance until the weight is about 1” above the base of the stand. • Take a balance reading. • Refer to discussion in the manual.

  15. VI. Single Fixed Pulley with Single Movable Pulley (pg. 9) • Unwind the long string near ring C. • Place the weight on the stand. Hook a single pulley to ring B on the stand. Grasp one of the hooks of the other single pulley and attach it to the weight (one should continue to hold it until it is connected later). • Take the long string attached to ring C and thread the string through the bottom of the lower pulley (right to left) and over the top of the fixed upper pulley (left to right). • Grasp the end of the paper clip and pull down gently so that the string remains taut.

  16. VI. Single Fixed Pulley with Single Movable Pulley (cont.) • Let go of the pulley and make sure the strings are still in the grooves of the pulleys. • Zero the balance. Hold the balance upside down and attach it to the paper clip at the end of the string. • Gently pull down until the weight is about 1” above the base of the stand. • Take a reading.

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