Exploring simple machines: Physics for young children
“Look!” calls Rachel. “We turned the wagon over. Come and spin a wheel with us.” Four children sit on the playground grass trying to make the wheels spin faster and faster. Meg stops her wheel and points to the long rod connecting the two back wheels. “It’s round too. Let’s see how fast we can make it turn.”
Look around: Where else do you see simple machines?
The wheel on a tricycle
The platform steps
Scissors at the art table
The pushpin on the parents’ bulletin board
A can opener on the kitchen counter
Making work easier
Physics is the study of matter (anything that occupies space) and energy (the ability to do work) and their relationship to each other. In the world of physical science, work is the force we exert to move something. A simple machine is a device that makes work easier by increasing force or changing the direction of a force—without electricity or other power sources. There are three basic simple machines: levers, pulleys, and inclined planes. Other simple tools—and the combinations that make complex machines—combine the attributes of these basic machines. Each gives its user the ability to maximize personal muscle strength as well as power from generated sources to move large and heavy objects—a load.
Levers help lift loads with less effort. A pry bar helps a gardener move a large stone; a jack lever makes lifting a car to change a flat tire possible; a stapler bends metal to fasten paper neatly; and an old-fashioned seesaw allows a child to lift a friend into the air. These and even a simple spoon or fork are all levers. A lever has three parts—the load being moved, the force or muscle power behind the move, and a fulcrum, the support or balance point against which the force is exerted.
In a Type 1 lever, the fulcrum is between the force and the load, as in pliers. In a Type 2 lever, the load is between the fulcrum and the effort. To open a nut with a levered cracker, for example, the nut is between the hinged end and the two handles. A Type 3 lever places the force between the fulcrum and the load. Tweezers, barbeque tongs, and a fishing rod are Type 3 levers.
Wheels and axles make it easy to move large and heavy objects overcoming some of the force of friction. Typically a larger wheel is fastened to a smaller cylinder or axle so that they turn together. When the axle turns, the larger wheel moves a greater distance with less force. The axle moves a shorter distance but needs more force to move it. Door knobs, wagons, and toy cars all move with wheels and axles.
Gears are toothed wheels. In a set of gears, wheels of different sizes link so that the larger wheels move a greater distance and more slowly than the smaller ones. Gears can transfer force from one part of a machine to another. Non-digital clocks, eggbeaters, and hand drills use gears to manage incremental movement.
Inclined planes are flat sloping surfaces over which objects or loads can be pushed or pulled to make the movement easier. Ramps, bridges, rooftops, roller coasters, a staircase, and the bottom of a bathtub are inclined planes. Each can carry or move a load more easily along an incline than in a straight line.
Screws have inclined planes called threads that wrap around a center shaft. Drill bits, bolts, grain grinders, and spiral slides are all examples of screws.
Wedges are two inclined planes placed back to back—a knife blade, an ax, a doorstop, and even your teeth—that split, cut, or fasten a load.
Pulleys are used to increase force and can change the direction of that force. A pulley is a wheel with a groove along its circumference. The weight of a load at one end of a rope, chain, or cord is moved with less force exerted at the other end because of the wrapped wheel between. Pulleys can be fixed and attached in a position over the load like a bucket at a well. Movable pulleys are attached to the load being lifted. Examples of movable pulleys at work include mini blinds, flagpoles, cranes, sailboat rigging, tow trucks, and clothes lines.
A complex machine is two or more simple machines that work together to make work even easier. Examples include a wheelbarrow (wheel and lever); a can opener (two wheels); and a keyed door lock (gears and wedges).
Exploring simple machines
Let children investigate, sort, classify, and count examples of real simple machines—wheels, screws, pulleys, inclined planes, and levers. Ask parents to share examples from home. Start simply and present one class of machine—screws, for example. Gather nuts and bolts, screw-top bottles and lids, pipe fittings, screws, and screwdrivers. Talk with the children about the threads—their distance apart, their sharpness, and the number on each machine. Help the children formulate ideas about why there are differences. Why use a screw-on fastener instead of a snap-on lid?
Build similar collections of other simple machine examples.
Challenge the children to identify specific attributes of the machines. Encourage them to stretch their understanding by identifying attributes that different machines have in common—a pulley, for example, has a wheel and axle.
A collection of the three types of levers offers children the opportunity to explore and discover simple machines. Encourage conversations about muscle strength—how does a lever make our muscles seem stronger. Demonstrate how to open a paint can with a lever. Ask the children for ideas on how else the can might be opened. Explore tweezers and tongs that offer precision and power. Investigate nutcrackers and help children identify and describe how each type works with a lever to make the work easier. Encourage children to make drawings of their investigations.
Pancakes and levers
A standard cooking spatula is a simple and accessible lever. Introduce it with play dough pancakes or the real thing.
Here’s what you need:
flat work area
variety of spatulas
1. Introduce the activity by suggesting that the children make pancakes.
2. Invite children to manipulate the dough, eventually directing them to smash balls of dough into flat disks—pancakes.
3. Introduce a variety of spatulas—toy and real, metal and plastic, narrow and straight, and wide fan-shaped tools.
4. Invite the children to evaluate the spatulas. Does one sort make the job easier than another? Let the children try to flip the pancakes and to move them from the table to a serving dish.
Gather information about children’s background knowledge about wheels with a simple transportation collage.
Here’s what you need:
1. Gather old magazines, junk mail, advertising brochures, and pictures printed from the Internet that feature vehicles with wheels: motorcycles, wagons, cars, big-rig trucks, airplanes, trains, busses, vans, tractors, and unicycles, bicycles, and tricycles.
2. Invite children to make posters of vehicles according to the number of wheels, the type of vehicle, the color of the vehicle, or another attribute.
3. Hang the posters in the classroom and encourage children to study the various vehicles and the wheels that move.
4. Build vocabulary by discussing the people who manage the different vehicles. Ask questions that help children distinguish between driver, pilot, captain, conductor, and farmer, for example.
Wheels and work
Introduce the word friction as you help children discover how wheels minimize resistance and make vehicles move more easily.
Here’s what you need:
cardboard milk cartons or small cardboard boxes
wooden thread spools or bobbins
flat-head roofing nails
empty table top or clear floor area
1. Help children investigate the force of friction. Use a length of tape to mark a starting line. Invite the children to place an empty box on the table at the starting line and flick it with a forefinger. Mark and measure how far the box moves.
2. As the children work to put wheels on the boxes, talk with them about how wheels make work easier.
3. You’ll need four similarly sized spools or bobbins for each vehicle. Position the spools on the nails and push the nails into the box in the same approximate place on each side.
4. Bring the wheeled boxes back to the starting line. Invite the children to again flick the box using the same amount of force as the first time. Again mark and measure the distance the boxes traveled.
Nuts and bolts
Match and compare this example of inexpensive simple machines.
Here’s what you need:
nuts in a variety of sizes and styles
bolts in a variety of sizes
1. Ask for donations or, for a few dollars, purchase the nuts and bolts. At a hardware store you’ll discover machine, wood, carriage, and metal bolts; and hex, wing, and acorn nuts. Both nuts and bolts are available in steel, galvanized metal, and brass in an array of sizes
2. Introduce the collection of nuts and bolts to the children. Demonstrate that several different nuts can fit on a single bolt.
3. Help children identify and name the similarities and differences and to explore sizes with words like smaller, larger, big, little, fit, and same.
4. Invite the children to sort the bolts by size.
5. Investigate weight with a balance scale. How many nuts weigh the same as three bolts, for example?
Small metal and plastic pulleys are inexpensive and available at hardware stores. Attach them to indoor and outdoor walls to offer maximum exploration opportunities.
Here’s what you need:
rope to fit the groove in the pulley wheel
2 buckets with handles
1. Set up the activity by tying one end of the rope to the bucket handle. Thread the other end through the pulley, along the groove in the pulley wheel, and down to the ground.
2. Introduce the activity by helping children understand how a pulley allows us to move and hold heavy weights with less muscle force.
3. Ask the children to fill both buckets with the same number of blocks or other heavy classroom materials.
4. Direct one child to stand next to the bucket that’s attached to the pulley. Pull the rope to lift the bucket into the air.
5. Direct the same child to lift the second bucket—without the help of the pulley.
6. Engage the children in a conversation that lets you evaluate how much they understand. Ask which activity took more effort or strength. Ask which way it would be easier to hold the bucket for a longer time.
Note: Remind children to lower the buckets slowly. Don’t leave the pulley unsupervised.
Wheels allow movement with less force.
Here’s what you need:
scooter board or wagon
large open area for movement
paper and pencils
1. Help the children examine the features of the scooter board or wagon. Talk with them about the size and measure the dimensions. Ask about the size, number, and the spacing of the wheels. Invite the children to sketch the vehicle.
2. Sit on the scooter board. Ask the children why the wheeled vehicle isn’t moving.
3. Invite them to help move the vehicle. Try to let the children work out how to move you—efficiency comes when they are all on one side pushing in the same direction.
4. After the children have been successful in moving you, ask to stop. Again, encourage them to problem solve. Ask if they can feel the scooter moving them before they stop it.
5. Invite the children to take turns sitting on the scooter board letting the other children start and stop the movement.
6. Evaluate the activity by asking the children if they think moving on the board is easier and smoother than sliding across the floor (or grass) without it. Is it easier to move a heavy weight (you) or a lighter weight (a child)? Invite the children to continue the investigation with loaded trucks and wagons.
Ramps, distance, and speed
Inclined planes set at different heights invite children to explore the characteristics of speed, friction, motion, and distance.
Here’s what you need:
wooden or plastic plank
variety of small balls
chart paper and pencil
1. Introduce the activity with free exploration of the materials. Ask for and record predictions on what happens when a ball rolls down a plank. How far will it go? Will it stay in a line or veer left or right? Will a big ball roll farther than a small one?
2. Place a line of tape along one edge of the plank to establish a starting line.
3. Set up the inclined plane with the taped end raised on a single block—a shallow incline.
4. Invite the children to roll different balls from the starting line. Mark and measure the places the balls stop.
5. Change the incline of the plane and repeat the experiment. Be sure to record the changes in how fast and how far the balls travel.
6. Help children review their predictions and compare them to the actual movement of the balls. Invite them to make a second set of predictions based on their new evidence.
7. Vary the experiment by changing the texture of the surfaces—rolling the ball down a carpeted ramp rather than a hard, smooth one or using a wheeled vehicle rather than a ball.
Children’s books that feature simple machines
Burton, Virginia Lee. 1978. The Little House. New York: Houghton Mifflin Books for Children.
Calmenson, Stephanie. 1992. Roller Skates. Logan, Iowa: Perfection Learning.
Carle, Eric. 1998. Pancakes, Pancakes! New York: Aladdin.
Douglas, Lloyd. 2002. What Is a Pulley? New York: Children’s Press.
Frazee, Marla. 2012. Roller Coaster. Pine Plains, N.Y.: Live Oak Media.
Hudson, Cheryl Willis. 2001. Hands Can. Somerville, Mass.: Candlewick.
Mosel, Arlene. 1993. The Funny Little Woman. New York: Puffin Press.
Rockwell, Anne. 2003. Big Wheels. London: Walker Childrens.
Willems, Mo. 2003. Don’t Let the Pigeon Drive the Bus. New York: Hyperion Press.
DeVries, Rheta and Christina Sales. 2011. Ramps and Pathways: A Constructivist Approach to Physics with Young Children. Washington, D.C.: National Association for the Education of Young Children.