This activity adapted from UC Boulder's Teach Engineering website.
This activity can easily expand to an hour lesson, and even longer with discussion at each group's tracks.
Students can build in pairs or in a larger group, up to four students is best.
It is helpful to have more than one building a run, so that one can hold the track in position while the other tapes.
The Play-Debref-Replay method of science teaching works great for this activity (see the resource).
Concepts covered can either be Energy transformations for older grades (potential, kinetic also sound, heat), or Forces on the marble for upper Primaries (gravity, friction), or Pushes and Pulls for lower Primaries.
Free experimentation activity:
The challenge: build a roller coaster for marbles. Discuss with students elements of a real roller coaster they have seen (loop, inclined loop, hill, corkscrew, banked curve... https://en.wikipedia.org/wiki/Roller_coaster_elements). Ask them to include two of these elements in the track they build for a marble.
Give each group 3 pieces of foam to build their track. Give them a cup to tape to end of their track so that the marble does not roll away.
Start Play. Students freely experiment to build tracks, encouraged to test it out continually as it extends if they are tending to build a huge track before running marbles down it. They will quickly learn what works and what does not.
Some tips for students, once they have been experimenting for a while, and if frustration creeps in:
Start as high as you can.
Make a loop smaller if the marble does not have enough energy to make it around a larger one.
Banking a corner (tipping up one side) might help keep a marble on track.
Debrief:
If time allows, gather the class around each track in turn to show their run, show cool features of their track, and explain how they overcame challenges, and if there is a feature they would like input on.
During this time, introduce some basic concepts and terms as age appropriate. For younger students stick with the forces on the marble - gravity pulls it down the track and friction slows it down. For older students discuss energy forms and transformation:
Potential energy ("gravitational energy", or "height energy" for younger students) is the energy the marble has from being high (most students intuitively start their track high, giving the marble a lot of potential energy to start it of).
Kinetic energy ("motion energy") is energy the marble has as it moves. It needs a lot of kinetic energy (i.e. must be going fast) to make it through a loop, or around a corner.
Energy is conserved as the marble moves, but is transformed between different kinds of energy. Starting high and stationary it has all gravitational potential energy, which is converted to kinetic energy as it rolls downwards. As a marble moves along a track its energy changes from potential to kinetic and back as it goes lower and higher. At the top of a hill it has a lot of potential energy, which changes to kinetic energy as it speeds up down the hill (and the PE drops). As it moves up a hill, it slows so loses KE, but gains PE as it gains height. Energy is conserved throughout.
The marble gradually loses all of its energy to friction with the track (rubbing against the track).
Friction generates thermal (heat) energy and sound, so when the marble comes to a stop all its initial potential energy has been converted to thermal and sound energy.
In a loop, if the marble is going fast enough, it will stay on the track. The marble wants to keep going in a straight line, so pushes against the track. The track keeps curving over, pushing back against it. A marble in a tighter loop will accelerate more than a marble in a wider loop. If the marble is not going fast enough, it will not push against the track enough and fall off.
Replay:
Return students to their own tracks, encouraging them to use other groups' ideas and incorporate into their own - engineers and scientists use each other's ideas all the time, and cooperate to make the best projects this way.
While circulating, insert the terms discussed during Debrief into conversations
Measuring and Graphing:
Students can measure the height of their tracks at various places and graph against a linear drawing of their roller coaster (see attachment for worksheet and photo). The height data correlates with the potential energy. Students can also indicate where the marble has most kinetic energy (where it is also losing the most PE).
Background information on real roller coasters:
A real roller coaster has no engine and once elevated to its start point is entirely driven by the force of gravity. At the start of the ride, which must be the highest point, the roller coaster has a certain amount of potential energy, and will not gain any more energy, but transfers PE to KE and back again, while losing both to friction.
Weightlessness and heaviness that you feel in a roller coaster car is from the combination of gravity and acceleration when the roller coaster changes direction.
More than 1g at the bottom of a hill (gravity gives 1g + acceleration down gives additional gs) - feels like you are being pushed down into the seat.
Less than zero gs at the top of a hill (negative gs from deceleration are greater than the 1g force of gravity) - feels as if you are being lifted up. Weightlessness can also be explained in this way: when the roller coaster car starts descent from the top of a hill, the riders and seat are both falling due to gravity, and without the force of seat pressing on them, the riders feel like they are weightless.
One ramp to vary height and object rolled down (younger students)
Each group of students sets up two ramps of different heights, and rolls a marble down each. As them to compare the speeds of the marbles i.e. which marble goes faster and ‘wins’. Students can measure the height that the marble starts at, to practice measuring. (Note that the ramps have to have quite different heights for the speeds to be noticeably different e.g. 20cm and 70cm).
Discuss why the marbles goes faster down the higher ramp. At the beginning of the ramp the marble starts with ‘height energy’ (called ‘potential energy’). With a higher ramp the marble has more height energy to start. The height energy of the marble changes into motion energy as it moves down the ramp. So a marble that starts with more height energy gets more motion energy so moves faster and goes further.
Ask students to compare rolling a pebble and a marble down their ramp. Make sure the tracks are the same height and the marble and rock are about the same size (so the only variable is the item being rolled down the track). A rock with a bumpy shape will rub against the track more - it has more friction. Friction is a force which slows things down. The marble can roll so it has little friction, so retains more motion energy and can go faster. Discuss other things that roll (anything spherical, wheels).
Kindergarten activity
Students work in pairs with two tracks only. Help them to tape the tracks together so that there are no tape bumps at the join.
If they want to include a loop help them to tape it together, although many Ks are happy with the hills and ramps that they create.
Discussion on why the marble rolls down the track: it is pulled down by gravity. Draw a hypothetical track on the board with an elevated end-point and discuss where the marble will eventually stop (at the lowest point).
U-track for marble collisions and energy transfer
Curve one track into a U shape and tape ends to two chairs. Use four marbles of different colours to roll down the track and try different starting positions to see how energy transfers between the marbles. (If the marbles are the same colour, students think that one marble goes through another rather than passing the energy to each other.) Marble collisions worksheet attached below.
