Marble Roller Coaster Topic Area(s) Cost Time Grade Level Supplies Gravity Potential/Kinetic energy Design Process Structures Friction $1.00/Child 30 min 6-12 Stopwatch or phone timer Scissors/utility knifes Marbles Tape Building materials such as newspaper or cardboard Curriculum Links Grade 6 Science Big Ideas: o Newton's three laws of motion describe the relationship between force and motion Grade 6 Content: o Newton s three laws of motion o Effects of balanced and unbalanced forces in daily physical activities o Force of gravity Grade 6 Science Curricular Competencies related to the experimental method, including data collection, analysis and evaluation Grade 7 Science Curricular Competencies related to the experimental method, including data collection, analysis and evaluation Materials (for class of 30, working in groups of 3-4) 10 Stopwatches (participants can use a timer app on their phones) 15-30 scissors or utility knives (if using cardboard) Large bag of marbles Tape measures, metre sticks, or string for each group Various materials such as tape, newspaper, foam pipe insulation, sticky tack, etc. A room or hallway with lots of space and props (tables, chairs, wall space) to incorporate into the roller coaster design! 1
Background Information Newton s Laws of Motion are three universal laws that allow us to understand and predict how objects move. They apply in almost all situations, excluding when objects are extremely tiny (Quantum Mechanics) or moving close to the speed of light (Relativity)! Inertia An undisturbed object will maintain its current state of motion. This means an object will not speed up, slow down, or change direction unless acted on by force. F=ma The net force of an object is determined by its mass and its acceleration. The same amount of force will cause a very small acceleration on a very massive object, and a large acceleration on a smaller or lighter object. Equal and Opposite Every force has an equal and opposite reaction. When you push a wall, the wall actually pushes back; this makes sense because if there was a net force on the wall, it would accelerate, meaning the wall would move! Friction is a resistive force that acts against two objects in contact moving relative to each other. Friction always acts opposite to the direction that the object is trying to move. When friction occurs between an object and a fluid, it s called drag, a common example of which is air resistance. Acceleration is the rate of change in velocity of an object. Velocity is both speed and direction, so if an object changes direction while moving, it is accelerating (even if it never speeds up!). The force that keeps an object moving in a circular path is known as centripetal acceleration. Can you use Newton s laws of motion to explain why you feel pushed to the outside of a circular path, even though you are accelerating towards the centre of rotation? Centripetal Acceleration www.physicsclassroom.com 2
Work is when an object is displaced by a force in the direction of the force. It can also be measured as a change in energy. W = F s Work equals force times change in position. Gravitational potential energy is the energy stored in an object as a result of gravity. Work is needed to act against the earth s gravitational pull and raise an object; the energy is then stored in the object until it comes to rest on the ground. PE = mgh Potential energy depends on the mass of an object and its height. Kinetic energy is the energy stored in an object as a result of it being in motion. Work is needed to accelerate an object to its current velocity; the energy is then stored in the object until it comes to rest at a complete stop. KE = 1 2 mv2 Kinetic energy depends on the mass of an object and its velocity. Conservation of energy is a principle that states energy can be converted from one form to another, but never destroyed. The Engineering Design Process is a series of steps that engineers use to help them solve problems. It is an iterative process that can be repeated as many times as necessary. Often, the problems that engineers need to solve are open-ended and have many possible solutions; this approach helps them avoid using the guess-and-check method, a process which is often inefficient in terms of both time and money. Procedure 1. Distribute starting materials (money, scoresheets, etc.) to each group. 2. Explain the challenge and scoring system to the class. Show students what materials are available to them in the store and how much each item costs. 3. Give groups time to plan their roller coaster and purchase additional materials. Encourage them to create a detailed design and budget while still managing their limited time. 3
4. Allow the students time to build, test, and modify their tracks. Have each group measure their own group and another group s track and features prior to the official testing period. 5. Have each group demonstrate their roller coaster and point out any special features. NOTE: Theoretically, the marble must make a complete run of the track for a group to score any points. 6. Award the winners of the challenge! Expand: Try changing the rules around, e.g. choose a specific target time that teams have to aim for. Changing or adding available materials can have a significant impact. Try incorporating mechanical elements with the use of servo arms and remote controls. Try a more structured planning and building process. Have teams start by sketching multiple design ideas and include details such as proposed length and materials. They can then rank each idea according to aspects such as cost, maximum possible points, and feasibility. Have them build and test their prototype and repeat the process as necessary! What Happened? You may have noticed that the higher up your roller coaster started, the faster your marble traveled. If you had any hills, each one had to be smaller than the one before it in order for the marble to reach the top. This is because the marble has the most potential energy at the top of hills, which is converted to kinetic energy as it goes down the hill (this is why the marble is fastest at the bottom of the hill it has the most kinetic energy). Climbing a hill higher than the previous one would require more energy than the marble had stored. Why can t you assume that the marble will make it over two or three hills in a row of the same height? This is because the potential energy of the marble isn t just converted to kinetic energy; some energy is lost to air resistance and friction between the marble and the track. This means the marble has less energy left to climb to the top of the hill, even if it just came from a hill of the exact same height. If you tried to build a loop in your track, you would ve quickly discovered that the marble must be moving very fast to stay inside the loop. This is because the inertial path of the marble as it enters the loop (the path that it would continue to travel if the track suddenly ended and the marble went flying off) must supply enough upward force to counteract gravity and the centripetal acceleration at the top of the loop. 4
Connecting Engineering to Your Classroom Roller coasters that you see at amusement parks function using the same conversion of potential to kinetic energy. The cars are pulled up the first hill using cables powered by an electric motor, and the rest of the track is powered entirely by gravity. However, energy losses in such a large structure are much greater than the losses in this activity. Air resistance and friction still dissipate the largest amounts of energy, but some is also lost to the vibrations of the cars and the track not to mention the energy it takes to make all that noise! When engineers build a roller coaster they have to be careful to meet safety standards so that no one gets hurt. They follow a similar process of brainstorming, then building and testing smaller size prototypes to identify potential issues. Real people don t actually get on the ride until it s been tested with sandbags or dummies, often hundreds of times. This step by step method that engineers use to solve problems is called the engineering design process. The Engineering Design Process This activity challenges you to think about the best way to solve a problem using limited resources and a finite budget the type of challenge engineers face every day. The best way to approach these problems is to identify the problem, come up with many ideas, and determine which is the best solution. This can be done by taking into account budget, safety, needs of the user, and testing to see which works best. Note that the option that works best isn t always the best solution, because sometimes it isn t safe to use or possible to build within your limit of time and money. (e.g. Gold is an excellent conductor, but you can buy much more copper for the same amount of money and works almost as well as gold for everyday tasks). In this activity, you were given the task you needed to achieve (build a roller coaster). In real life, however, engineers may start from any point in the cycle, and repeat the process or certain steps many, many times. 5