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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 ClassIt’s as easy as:1 2 3F L E The number stands for the class. The letter stands for what’s in the middle.
ABC Baby you and me!
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