Levers

There is an updated version of this post here.

balance

During our Simple Machines unit, we learned about levers.

Key Concept of Levers:

You place a long bar onto a fulcrum (pivot point). You apply force in one direction, and the pivot point re-directs the force in another direction. You may need the same weight, or more weight or less weight on one end to lift the other end… all depending on where the fulcrum is.

If you’re working with small kids, you can stick to that basic point, and skip all the details I’m about to give on classes of levers!

First Class: There are three classes of lever. A first-class lever has the fulcrum in between the effort and the load (e.g. between you and the weight you’re trying to lift). You push down on one end, and the other raises up.

first class

If the fulcrum is in the middle (like on a seesaw or a balance scale), then to lift ten pounds of weight, you’d need to apply ten pounds of force. There’s not a mechanical advantage (i.e. the lever doesn’t let you lift anything heavier than you could normally lift). If you place the fulcrum very close to the load, and have a long bar to press down on, this gives you a mechanical advantage – it makes it easier to lift the load.

first MA

Second class: The load is in between the fulcrum and the effort. The best example is a wheelbarrow. You lift up on one end, and the fulcrum rests on the ground.

second class

Third class: The effort happens between the load and the fulcrum. “A hammer acts as a third-class lever when it is used to drive in a nail: the fulcrum is the wrist, the effort is applied through the hand, and the load is the resistance of the wood.  Another example of a third-class lever is the human forearm: the fulcrum is the elbow, the effort is applied by the biceps muscle, and the load is in the hand.” (Source)

third class

A Demonstration:

A see-saw is your ideal demonstration. You can put similar size kids on each end, and they see that it balances out. Then you can put an adult on one end, and see how many kids you need to lift the adult. And then you can try having the adult sit in the middle of the beam on their side, and one kid sit all the way at the end on their side and search for the balance point.

If you don’t have a see-saw, can you create one? It may be hard to easily build something strong enough (and safe enough) to lift an adult and kids, but you could lift a basket of books using something as simple as giant tinker toys.

I’ve listed several activities below. I’ve divided them by which class of lever they are. (I think I’m right on all these – let me know if you disagree!) But again, you can ignore the whole idea of different classes of lever and just treat them all as “levers” if that’s better for the age group you’re working with.

First-class lever activities:

See-saw: See above.

Balance scale: If you have a balance scale, this is a great time to get it out and let the kids experiment.

IMG_20150418_105322699

If you don’t have a scale, you could also build one with a variety of materials, including Tinker Toys (see top of post) or K’NEX.

scale

Or you could build a balance with a coat hanger: http://inspirationlaboratories.com/balancing-with-mms/

Or, with Dixie cups, string, and a popsicle stick. (See my post on measurement.)

Crow bar: Use a crow bar to pry up a heavy load. Or use a stick balanced over a small rock to lift a big rock. Or use a stick balanced over a brick to tip a cinder block over. Or take a pencil, and a ruler and a book: use the pencil as your fulcrum. Put one end of the ruler under the book, and then press down on the other end of the ruler.

Claw hammer: When you use a claw hammer to pull out nails, you’re using it as a first class lever. If you had the kids pound golf tees into something for the wedges lesson, they can use the claw hammer to pull them back out!

claw

Catapults: Put a pencil on the table (your fulcrum). Balance a popsicle stick over it (your bar). Put a pompon on the lowered end (your load). Strike the other end. The pompon flies into the air. Your kid may repeat for hours. More catapult ideas in this post.

IMG_20151003_094219761

Second-class levers:

Wheelbarrows: If you have access to a wheelbarrow, they are GREAT toys for outdoor time. Let the kids load them up and move them around.

Bottle opener: Let your child open a bottle of soda with a bottle cap.

Third-class levers:

Human arm: We had paper arms kids could decorate, then cut, then fasten together with a brad to create an elbow joint. Then they used yarn to represent the muscle.

IMG_20151003_094230834

Shovel, rake, or broom: When you use one of these tools, you have one hand at one end, serving as the fulcrum. The other hand is part way down the handle, providing the effort. (You could also use a stick to hit a piñata to demonstrate the force.)

Baseball bat: In addition to helping you lift loads, levers can also be used to speed something up by giving it a push. During outside time, use a baseball bat, or tennis racket, or other tool to demonstrate. Your hands are the fulcrum.

Double levers:

Tongs, tweezers, pliers: You could fill a sensory bin with pom poms and tongs. You could get a dried corn cob, and let kids use tweezers to pick out the kernels. Kids could use pliers to pull nails out of something (like pull the golf tees out of the pumpkin from the wedges activity!)

Scissors: Scissors are a double first class lever. Let kids have some scissor practice. (Like cutting out the arms for the activity above.)

Nutcracker: A nutcracker is a double second-class lever. If you’re not a nut-free facility, cracking walnuts open can occupy kids for hours!

Hammer: When a hammer is used to hammer in nails, it’s a third class lever.

Creation Station: In our classroom, we have a creation zone filled with recyclables (toilet paper rolls, margarine container lids, and so on), and small dibs and dabs (buttons, interesting pasta shapes, shells, plastic gems, and so on). There’s always an open table with some glue and kids are allowed to create anything they want. The oldest child in our Inventors Lab creates something fabulous each week, tied into the theme. On levers week, she built this seesaw.

IMG_20151003_151208151

Building toys: We also have one room called “The Construction Zone” where we put out various building blocks or other supplies. This week we had giant tinker toys. In the picture at the top of this post, you can see what a dad and child created… it was a see-saw like balance scale, but notice that on the end near the child there are free-floating discs. Those are weights that can be slid back and forth to adjust the power of the lift.

Snack: Use scissors to cut something – like pita bread. Use forks or chopsticks to eat with.

Addendum: Next year, we’ll add in this Duplo seesaw project.

IMG_20160802_173540517

Advertisements

7 thoughts on “Levers

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s