Levers and Pulleys

Levers A lever is a tool that people use to make work easier. Levers are used to lift things or overcome resistance. Levers give us an advantage by making work easier.

Vocabulary The lever arm is a stick or beam, that can pivot or turn at a point. The fulcrum is the point around which the lever arm pivots or turns The mass lifted by the lever is the load. The effort is the force (push or pull) needed to lift or pull the load

Challenge: Set the load at 15 cm. Can you lift load using 1 finger? Does it always take same effort to lift load? Where should you press to lift load with least effort? Discuss in groups: What advantage can be gained by using the lever to lift the load? How can you measure advantage provided by the lever?

Practice reading spring scale Spring scales measure the effort needed to lift the load Effort is a force. Force is measured in Newtons. Use the scale right side up. Hang it, and pull down on bottom hook. The amount of force is read directly from the scale. Spring scale

Rules for using scales: Always be sure the scale reads zero. Use it right side up, not upside down. Pull until the lever arm is level, then read the scale in Newtons. Stop before the scale goes past 10 N. Additional rules – scale readings are made from the top of the metal bar Each little line represents.2 N. When indicator is between 2 lines, students should estimate to nearest.1 N.

How much force is necessary to lift load? A scale is helpful to determine how much force is necessary. Force is measured in Newtons Today, the load stays at 10cm. Effort is applied at different distances from the fulcrum. Record the scale reading on the left side of the effort column.

Lever Experiment A Demonstrate the force of the scale: Put load 5 cm from fulcrum. Put scale 25 cm on other side. Pull down to balance. Read scale. How can this be?

Lever Experiment B Using the graphs for both Lever Experiment A and Lever Experiment B, answer this question. Where should you put the load, and where should you put the effort, for the greatest advantage? Where is it easiest to lift the load?

Lever Classes Does the fulcrum always have to be in between the load and the effort? If the fulcrum is not in the middle, is it still a lever? Is there an advantage to moving the fulcrum to a different position on the lever arm?

Lever Class It’s as easy as: F L E The number stands for the class. The letter stands for what’s in the middle. ABC Baby you and me!

Remember 123 FLE Label each drawing and then identify the lever class

Real Life Levers Go back to the first slide and label the fulcrum, the load, and the effort. Then identify the class of lever.

Pulleys A wheel with a grooved rim in which rope can run to change the direction of the pull that lifts the load. Task: How can a pulley be used to lift a load?

Pulley’s Advantage Pulleys can give two kinds of advantage: Reduced effort is called mechanical advantage Pulleys can also change the direction that the effort is applied. That is called directional advantage.

Pulleys Lesson 2 How are fixed and movable pulleys the same? What kind of advantage is produced by each system? In what way are levers and pulleys the same? Is there any advantage to using two pulleys at the same time?

Drawing Pulley Diagrams Draw an anchor point at top Draw large dot to show where rope attaches. Draw lines to show how rope goes around pulley Draw load and effort using same symbols and letters