Kinetic and Potential Energy
Rube Goldberg Machines
The object of any Rube Goldberg machine is to build a machine to perform a simple task using as many different steps possible in a chain-reaction.
the materials you will need vary greatly depending on the steps you decide to incorporate into your invention
Note: be sure that the adult(s) in charge agree to the materials you use and the way in which you intend to use them before you start.
First, you will need to decide on your simple task. It is often helpful to start with the last step first and work backwards.
The different steps you may choose might involve some or all of the following:
- a marble run (see below)
- a domino run For inspiration, check out these clips from Domino Day (an annual quest to break the domino run world record) Domino Day 2008 Domino Day 2010
- weights and pulleys--such as a step that adds an item to a bucket on a pulley, thereby causing the bucket to lower and raising the item attached to the other end of the string
- a chemical reaction, such as adding some vinegar to a balloon filled with baking soda to cause it to inflate, or using Alka Seltzer and water, or Mentos and diet cola in a similar way
- popping an inflated balloon to release another item (you can attach a thumbtack to a vehicle or pendulum etc. to do this)
- a teeter-totter (lever) effect, or a sideways teeter totter that rotates
- ramps (these go well with tracks)
- an electrical circuit--causing a circuit to connect or break in order to start or stop a motor (ie. a start a fan that blows a toy car away on a track to hit a button or cause a domino to fall), light an LED, make a sound, start an electric train, etc.
- a release mechanism--perhaps to start a rubber-band vehicle in motion (see below) or a vehicle with pull-back and go action or a sling-shot, etc.
- using temperature, such as melting an ice cube in order to effect a change in weight (by letting water run off a surface etc.) or heating something (with adult approval!)
- causing expanision by adding water to a "grow" toy (like the dinosaurs you can add water to and watch grow)
- using a rachet and/or cam system to regulate the fall of a series of marbles, the rotation of a weight on a string around a pole, etc.
- wooden train sets (a more mature use for the Thomas set you couldn't part with!), or Hotwheels etc. make good track systems for rolling vehicles and/or marbles
- cause a slow leak in a container of water, flour etc. that causes a weight change (and works a pulley, or fills a vehicle/container to effect another change)
- incorporating a small xylophone, whistle, bell or windchimes into your design helps add interest and mark your progress when things get moving
- you can also try following a theme in your design
- if you are older and have adult permission and supervision, you can also try using electric trains, heat/fire, boiling water, popping popcorn, sprayers, etc. in your machines, as found in some of the videos below
For more inspiration, check out these YouTube videos of Rube Goldberg machines in action
A few years ago, Honda released an ad that used a Rube Goldberg machine
Also, see these:
Ok Go Rube Goldberg Music Video
University of Toronto National Engineering Month 2010 Rube Goldberg Machine
2007 National (US) Rube Goldberg Contest @ Purdue
Homemade Marble Run
choose from what you have on hand:
cardboard tube from gift wrap, paper towels and bathroom tissue
masking tape and/or duct tape
any tracks from toys such as toy trains, Hotwheels, etc.
plastic, rubber or metal tubing (both flexible and rigid are useful)
several marbles and/or small bouncy balls and/or ping-pong balls (choose balls that fit through your tubing)
cardboard and boxboard boxes, chairs (check with your adult first) and other items useful for structural support
adult weilding a hot glue gun
- Lay out your materials and experiment with their arrangement until you have an idea of how you would like your marble run to look. Flexible tubing makes great loops and corkscrews.
- Start taping your run together. Try it out a few pieces at a time to ensure your marbles/balls don't run off the track or get stuck. You may need to trim the edges of the cardboard tubes at an angle to accommodate bends, tuns and drops.
- Another way to vary directions etc. is to cut a hole in the bottom of a tube to allow for drop-through.
- Glue or tape your sections together and try it out. Adjust as necessary.
- Try making two runs the same length and racing, or add some other kinds of motion to make your own Rube Goldberg machine (see above).
In which centripetal force saves the day! (But just in case--try this outdoors first.)
a small bucket with a sturdy handle
a short length of rope
- Fill the bucket about 1/2 way fill with water.
- Tie the rope to the handle with a strong knot.
- Holding the rop about 8-12" (20-30 cm) above the handle, swing it gently so that you get a pendulum action happening.
- Using this action, when it gets to just about horizontal, continue the swing relatively quickly so that the bucket now rotates in a circle.
- Stopping it without spilling is tricky and requires excellent timing. When it reaches horizontal coming down, use your other hand to gently slow it until it stops.
- If it spilled, you probably didn't have enough speed on your swing.
- How do you think engineers use centripetal force when designing roller coasters?
Check out this link to see more roller coaster related physics.
Salad Spinner Art
In which centripetal force creates masterpieces of art.
a salad spinner with a flat bottom on the inside
white drawing / painting paper
non-toxic tempera paint of various colours
optional: newspaper or similar to protect the table/floor from mess
- Cut the paper so that it fits snugly into the bottom of the spinner.
- Dab a few blobs of paint around your paper.
- Place the lid on the spinner, then spin.
- What do you notice about the path the paint takes when the spinner is spun?
Rubber Band Vehicles
This project takes advantage of the energy stored by the twisted rubber bands whose elasticity helps create potention (and then kinetic) energy.
Materials for boat:
a piece of pine or other solid wood betwee 4"x 6" and 6"x 9" and about 1" thick (10 x 15 cm and 15 x 24 cm and ~2-3 cm thick)
an adult weilding a jig saw, or supervising you using a manual coping saw
one or two small c-clamps
sand paper (medium grit is best, but any should do)
two small wood screws
a screwdriver that fits the wood screws
two thin pieces of board, such as those found on clementine or mandarin orange crates cut into rectagles ~2" x 3" (5 x 7 cm)
an elastic band
optional: water proof paint and brushes for decorating
- You will first need to cut your wood into shape. Mark the centre point on the short edge of the wood. Starting about 1/3 down either long side of the wood, lightly mark a curved line that meet at the centre point. Even up the sides so that your boat will be symmetrical. You can try drawing this out on paper then trace it to be sure the sides are identical. This will form the bow of the boat. Have your adult cut along the lines, or if you have adult supervision and permission you can make the cut yourself.
- At the opposite end of the boat, find the centre line and mark it. Now measure the longest side of your thin pieces of board and add 1 cm (1/2"). Now divide the total in half and measure and mark that distance from either side.
- Now measure the width of the thin pieces. Mark that distance from the back of the boat inward along the centre line. Connect that point to each of the two lines you just drew. Now cut out that section. This is where the propeller will sit.
- Sand down any rough edges.
- On the back edge of the boat, midway between the edge and the propeller slot, screw in one of the wood screws about 2/3 of the way into the wood. Repeat on the other side.
- On each of the thin pieces of wood, mark the half-way point between the two longest edges at the centre and continue the line to the edge of the piece. Cut a slot along these lines so that the thickness of the slot matches the thickness of the wood. Slide these together slot-to-slot, sanding and adjusting as necessary.
- To power the boat: Thread two blades of the propeller into the rubber band and attach one end of the rubber band to one screw and the other to the other screw. Twist the propeller back so that the rubber band twists around until it is very tight. Set in water and let it go.
Rubber Band Car
2 axles (bamboo skewers)
corrugated cardboard: 2 4"x 6" (10 x 15 cm) or larger and 1 6" x 4" (15 x 10 cm) or larger pieces or a narrow block of wood
if using a block of wood, you will also need 2 wood screws and screwdriver and a drill with a long enough bore to drill through the entire width of the wood (for the back axle)
scissors and/or small coping saw
if using a box or coardboard, you will need a brass fastener
a hammer and nail for making holes in the wheels
2 sets of wheels: choose from 2 identical thread spools or 2 film cannister lids or 2 identical juice bottle caps or two frozen juice lids for each set of wheels (the front and back wheels do not need to match)
an elastic band
a small flat metal paperclip
an adult weilding a hot glue gun
optional: paint and brushes, stickers, etc. for decorating
optional: extra rubber bands or cross-sections cut from a balloon to add to the wheels to improve traction
This plan follows similar principles to the boat above.
- First make your car body. You can use a block of wood, corrugated cardboard or a small box for this. See the diagram for a suggested shape. Note that the axle is in grey at the bottom of the slot. The black dot will be the anchor point for the rubber band (wood screw or brass fastener, see below).
- The wood willl need a hole cut through the width near the back and another at the front in order to accommodate the axles, so it is a good idea to keep those part fairly narrow yet wide enough at the back to accommodate a slot for the rubber band. The slot should be at least 1 cm (1/2") wide. Just in front of the slot, screw in the wood screw so that it is about 2/3 into the wood.
- If you use corrugated cardboard, you will need to cut 3 pieces as follows: 2 ones in which the corrugations run front to back and one (to be placed in the centre and which will also become the axle) in which the corrugations run side-to-side. In the front-to back pieces, cut the notch for the elastic so that it is 1 cm deeper than the side-to side piece. Glue the pieces together using white glue and let dry. In the middle piece that extends a bit more into the slot, you will need to poke a hole and insert a brass fastener. This will be where the rubber band attaches.
- Use the hammer and nail to poke a very small hole through one of the rear wheels. Use this as a template to mark the spot where you wish your axle to be (lower down on the car will give you better clearance on uneven surfaces). Have an adult drill a hole through the width of the back of the wood or carefully punch a hole through your box in that spot and repeat on the other side.
- Make a similar hole in the second back wheel using the hammer and nail. Enlarge each hole only as much as necessary to ensure a tight fit. The wheel and axle need to rotate together.
- Attach one wheel to the end and use the glue gun to affix it on the end of the skewer.
- Check the axles by inserting the skewer into the drilled hole (if using wood) or through the corrugations of the centre piece of cardboard near the back (if you are using cardboard). The axle will need to rotate freely, so enlarge to hole with the drill bit and/or by wiggling the axle until it moves freely. If you are using wood, you may wish to rub some candle wax on the axle to help it move better.
- Thread the loose end of the skewer through one of the axle holes passing through the centre andd out the far hole.
- Fasten on the far wheel as you did for the first. Centre the axle before proceeding to the next step.
- Use the hot glue to fasten a paperclip to the centre of the axle. Once cool and dry, this join must be rigid and strong enough to hold under the tensions of the stretched rubber band.
- Loop one end of the rubber band through the paperclip. Loop the other end through the first end and pull tight. Attach the longer loop to the wood screw or brass fastener.
- Attach your front wheels as you did for the back, skipping the paperclip/rubber band steps.
- To run your car, wind up the rubber band by either pulling your car backwards or pick it up and use your hand to wind it. Line it up and let it go!
Larger flywheels have been used historically in lumber mills and can be found in most cars, many factories, and NASA is even working on them as a reliable substitute for chemical batteries.
a two-wheeled multi-geared bicycle (it needs a wheel that can continue spinning once the pedals are still)
two strong magnets
a length of copper wire (the longer the better)
duct tape or masking tape and/or rubber bands for attaching magnets to the bike
a small LED bulb
- Turn your bike upside down and balance it on the seat and handlebars.
- Pedal the bike with your hand for several revolutions, then let go. Notice how long your back wheel keeps spinning even after your stopped?
- Try changing gears to see which gearing allows for the longest rotation after pedaling for a set number of rotations.
- Now, tape one magnet to the rim or tire of the back wheel.
- Wrap the wire around the other magnet, leaving a bit of length at either end of the wire.
- Wrap one end of the wire around one of the LED leads and the other around the other lead.
- Tape this to the frome of your bike in a place near where the magnet on the wheel will pass when the wheel is spun. Do not tape over the wire leads as you may need to make an adjustment.
- Pedal the bike and watch the LED. Does it flicker?
- If the LED does not flicker, try switching the leads. Most LEDs will only work in one direction, so changing the polarity may be necessary.
This is a simplified generator. Larger generators, such as those on hydro turbines (you can see these at Niagara Falls), wind turbines and fossil fuel power stations all work in a similar way, by spinning magnets to create a electricity. Thanks to Michael Faraday who first noticed that electicity has a magnetic field and made this connection!
Pendulum of Peril
a length of rope or twine
a sponge soaked in water
a person to hold the rope
a person to release the rope
a brave volunteer (or a coward who understands physics!)
- Tie the wet sponge to one end of the rope.
- The rope holder stands at the centre. If this person is not tall, it may be necessary to have them stand on a stool or chair.
- The other two people stand a ways to the side. They must be immediately beside each other.
- The rope releaser brings the sponge end of the rope up immediately beside the profile of the brave person, keeping the rope straight and taut.
- On the count of three, the releaser lets go and the brave person must stay in place without moving.
- If everyone has done this without moving, the pendulum should swing back just shy of the brave person.
- Try this a few times trading places and making predictions for the height of the pendulum swing. Can you find any other patterns?
- What forces cause the swing to lose height?
- What do you notice about the timing of the higher swings compared with the lower swings?