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Activity

Roller coaster

Summary: 
Build a marble roller coaster from foam tubing and masking tape. Incorporate features of real roller coasters and learn about potential and kinetic energy.
Science content (2016 curriculum): 
Physics: Motion and Forces, Newton’s Laws, Gravity (K, 2, 6)
Physics: Energy forms, Conservation of Energy (1, 3, 4, 5)
Materials: 
  • foam pipe insulation, 6ft by 3/4 inch
  • masking tape
  • marbles
  • optional: metal balls the same size as the marbles
  • boxes, chairs and other supports for sections of the roller coaster
Procedure: 

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).

Free experimentation activity:
The challenge: build a roller coaster for marbles. Include at least one of each of these elements: a loop, a hill and a curve.
Students freely experiment to build tracks, encouraged to test it out continually during building, 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.
Loops that are smaller will slow the marble down less.
Banking a corner (tipping up one side) might help keep a marble on track.

After some time gather the class around each group in turn to show their run, show cool features of their track, and explain how they overcame challenges.
Encourage students to then 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.

At some point, introduce some basic concepts and terms as appropriate:
Potential energy ("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 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 acceleration 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.

Students could name the sections of their track and draw a graph of the PE and KE going up and down along the length (see photos).

Allow students to work on their track some more, using ideas from other groups, and possibly inspiration from real roller coaster elements e.g. corkscrew, inclined loop (https://en.wikipedia.org/wiki/Roller_coaster_elements)
As they work, talk to them in terms of energy.

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 transfer 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+acceleration down). Less than zero gs at the top of a hill (from deceleration being greater than the force of gravity). 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.

Structured activities on force, motion and friction:
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).

Attached documents: 
Notes: 

I started out thinking groups would combine their tracks to make one big one, but students are very resistant to move a track they have spent time perfecting. Better to start students out in groups that they will stay in.

For spaces without much stuff to build on, make a pegboard to plant supporting upright rods: http://makeitatyourlibrary.org/workshop-play/marble-machines-board#.Vkdy...

When the initial hill was higher than 2m, the speed of the marble on initial descent made it challenging for it to stay on the track.

Grades taught: 
Gr 2
Gr 4
Gr 5
Teacher: 
Ingrid
Shelley Weir
Teaching site: 
General Gordon Elementary
ingridscience afterschool