Levers Objective 4 07 Determine how people use

Levers Objective 4. 07 Determine how people use simple machines to solve problems.

• A lever is a bar that pivots around a fixed point called a fulcrum. When a force is applied to part of the bar either by pushing or pulling, the lever swings about the fulcrum and overcomes a resistance force. The seesaw is a good example of a lever. If you sit down on one end of the seesaw and a heavier person sits on the other end, their downward force will cause your end of the seesaw to move in the other direction—up.

• Using a flat-head screwdriver to pry open a paint can is another example of the use of a lever. When you push down on the screwdriver, the lid of the paint can moves up. Therefore, the screwdriver changes the direction of the force. The fulcrum in this example is between your push of the screwdriver (input force) and the upward movement (resistance force) of the lid.

• There are different types of levers, depending on where the load, the effort, and the fulcrum are positioned. For this reason, levers are classified into 3 separate groups: Class 1, Class 2, and Class 3.

Class 1 Lever • This is where the fulcrum is between the load and the effort. • One example would be using a screwdriver to open a can of paint (see Diagram 4). In this case, the screwdriver is the lever. The load is the resistance of the lid of the paint can, the effort is the force that the person applies to the lever, and the fulcrum is the outside rim of the paint can that helps you to lever up the lid.

• Imagine how much harder it would be if you had to lift the lid off a paint can with your fingers, without the help of a lever! The screwdriver provides a mechanical advantage (a smaller force is being used to overcome a larger load). • The direction of the force is also being changed by the lever. Pushing down on the lever (the screwdriver) raises the load (the paint can lid). • Other examples of Class 1 levers include using a bottle opener to open a bottle of drink, using a claw hammer to pull out a nail, and playing on a see-saw.

Class 2 Lever • This is where the fulcrum is at one end of the lever, the effort is at the other end, and the load is in between. • One example would be a person lifting a load in a wheelbarrow (see Diagram 5). In this case, the wheelbarrow and its handles are the lever, the load is the weight in the wheelbarrow, and the force applied by the person lifting the handles is the effort. The fulcrum (the balance point of the lever) is the axle of the wheelbarrow.

• The mechanical advantage (remember, this is what makes the load easier to lift) is created by having the load closer to the wheelbarrow axle (the fulcrum) than to the person lifting the handles (the effort). • Other examples of Class 2 levers are staplers that staple sheets of paper together, and nutcrackers that have the hinge at the end of the machine.

Class 3 Lever • This is where the fulcrum is at one end of the lever, the load is at the other end, and the effort is in between. These levers involve using a large effort to move a small load a long distance. • An example is a person playing golf (see Diagram 6). In this case the golf club plus the person's arms is the lever, the golfer's shoulder is the fulcrum, the force being applied to the golf club by the golfer's hands is the effort, and the load is the weight of the golf ball.

• The aim is to use a large force for a small distance (the effort applied to the golf club by the golfer's hands) to move a small load (the golf ball) for a much larger distance. • This type of lever often trades distance force. You can use a large force for a small distance to move a small load for a larger distance. Other examples are using a baseball bat, a tennis racquet or a hockey stick to hit a ball, and a fishing rod to cast a fishing line.

THREE Classes of Levers Use this to help you remember the classes, FLE 123 (F = fulcrum, L = load, E = effort)

Levers in Balance • For a lever to be in balance (not moving) the forces trying to turn it in one direction (the turning effect) will be exactly balanced by the forces trying to turn it in the opposite direction. • A see-saw is actually a lever with a fulcrum in the middle (see Diagram 7). Think about a see-saw that is balanced, with two people sitting at different distances from the fulcrum. If one person is twice as heavy as the other, the lighter person must sit twice as far away from the fulcrum as the heavier person for the see-saw to be balanced.

• This is because the turning effect depends on two things - the size of the force (in this case the weight of the people), and the distance from the fulcrum. Longer levers give more leverage than shorter ones. Therefore, the smaller person has to create greater leverage to balance the heavier weight of the other person by sitting further away from the fulcrum. Once balanced, it requires very little force for each person to push the see-saw up and down with their legs.

Review 1. Which simple machine is defined as a rigid bar that is free to move about the fulcrum when an effort force is applied? A. wheel and axle B. inclined plane C. screw D. lever

2. An example of a second-class lever is a _______. A. seesaw B. door C. shovel D. crowbar A class 2 lever has the resistance or load in the middle, the fulcrum at one end and the effort at the other. An example of a class 2 lever is a wheelbarrow, where the front wheel is the fulcrum.

3. A broom is considered a third-class lever. The fulcrum is ________. A. In the middle of the lever. B. At the end opposite the one you hold C. At the end you hold D. missing A class 3 lever has the effort in the middle, the fulcrum at one end and the load at the other. An example of a class 3 lever is a broom.

4. An example of a first-class lever is a __________. A. scissors B. wheelbarrow C. tweezers D. fishing rod A class 1 lever has the fulcrum in the middle and the load and effort on either end. The fulcrum does not have to be geometrically in the middle of the fulcrum; the important thing is that it is between the load and effort. This seesaw is an example of a class 1 lever.

5. A baseball bat can act as what type of simple machine? A. pulley B. wheel and axle C. lever D. screw

The End!!!