Balloon Car Category: Physics: Force and Motion Type: Make & Take Rough Parts List: 1 4 2 2 1 1 Balloon Wheels Pieces of straw Dowels or bamboo skewers Small piece of ½” PVC pipe Piece of cardboard Tools List: Masking tape 13/16” paddle bit Hot glue gun Utility knife Drill bit, same diameter as dowel Video: http://www.youtube.com/user/FresnoCSW/videos How To: Cut a slit in the cardboard, careful not to cut all the way through the cardboard. Cut a hole in the side of the cardboard with the paddle bit (no drill necessary). © 2012 Fresno Community Science Workshop. All Rights Reserved worldwide. When linking to or using FCSW content, images, or videos, credit MUST be included. Bend the cardboard and place hot glue into the slit to hold it up for reinforcement. Cut and glue two pieces of straw onto the bottom of the car. It works best if they stick out past the edge of the cardboard. Drill or punch a hole through the center of each wheel. Push a dowel through the hole of two wheels. Slip the dowels through the straws and connect the remaining two wheels. Glue the wheels onto the dowels from the outside. Wrap the mouth of a balloon around the PVC and tape it in place. Push the PVC through the hole in the cardboard and glue in place. © 2012 Fresno Community Science Workshop. All Rights Reserved worldwide. When linking to or using FCSW content, images, or videos, credit MUST be included. Blow up the balloon, place the car on a flat surface, and watch it drive away! Fine Points: → It is easiest to fit a balloon around ½” PVC pipe than around a larger diameter pipe. → The size of the paddle bit should be the same size as the outer diameter of the pipe. That’s 13/16th for ½” pipe. → Weight may need to be added onto the back of the car to make it run better. Concepts Involved: •
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Pressure is a force over a certain area. The force of air molecules pushing on the walls of the balloon is called air pressure. An outside force is needed to propel an object forward. Focus Questions: 1. What happens if smaller balloons are used? Larger balloons? 2. What would happen if multiple holes were drilled so that more than one balloon could power the car? 3. How would the car work if you put a larger or smaller tube at the mouth of the balloon? Elaboration: Everyone knows that you have to push something to get it going. More technically speaking, a force is required to get something to move from a standstill. This was #2 of Isaac Newton’s three laws of motion. It is usually expressed with an equation: F=ma. An approximate English translation for this mathematical expression would be: A force (F) applied to an object will give a change in velocity (acceleration, a) that depends on the object’s mass (m). Thus, if you have no force, you have no acceleration. Pressure is a force applied over a certain area. The inside of a balloon has a certain area, and when you blow up the balloon, the elasticity of the balloon squeezes the air inside. When you tie the balloon, this is a situation of equilibrium, with the air inside pushing out with exactly the same pressure as the outside air and the balloon’s elasticity combined pushing in. When forces are all in equilibrium, there is no acceleration, that is, if things are not already moving, they don’t start moving. When you open the mouth of the balloon, now you’ve ruined the equilibrium. The up-­‐down pressures are still in equilibrium, and the side-­‐to-­‐side pressures are still in equilibrium, but the front of the balloon has a good bit of pressure pushing on it from the inside while at the back of the balloon the air is rushing out, © 2012 Fresno Community Science Workshop. All Rights Reserved worldwide. When linking to or using FCSW content, images, or videos, credit MUST be included. that is, the air is not pushing on the balloon at all. The result is a force on the front of the balloon in a forward direction, perfect for getting the car to move forward. Forces come in pairs. This was Newton’s third law of motion: for every action there is an equal and opposite reaction. In this car the action is the air rushing out the back of the car. The reaction is the car being pushed forward. This is not usually how a car goes! Usually, the forward force comes from the tires on the road. The action is the cars pushing the ground back, and the reaction is the car moving forward. The tires get their force from the drive train, which in turn gets its force from the engine. Inside the engine, petroleum is combusted with oxygen giving force due to the expanding gases produced in the chemical reaction. Thank goodness we don’t have to put all the force in to our cars by blowing up balloons before we go somewhere. Experiment with balloons of various sizes and shapes to change the speed and distance the car can travel. Also try different sizes of pipe. Small balloons allow the car to travel fast, but only over a short distance because the air escapes quickly. Larger balloons propel the car further because the balloon holds more air, but the force exerted by the escaping air is not as great as that from smaller balloons so the car will not travel as fast. Medium sized balloons should provide the best results; traveling further than the car with the small balloon, yet faster than the car with the larger balloon. Of course what is considered to be “the best result” depends upon whether you are judging for speed, distance, or the two combined. Links to k-­‐12 CA Content Standards: Grades k-­‐8 Standard Set Investigation and Experimentation: Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other strands, students should develop their own questions and perform investigations. Grades k-­‐12 Mathematical Reasoning: 1.0 Students make decisions about how to approach problems: 1.1 Analyze problems by identifying relationships, distinguishing relevant from irrelevant information, sequencing and prioritizing information, and observing patterns. 1.2 Determine when and how to break a problem into simpler parts. 2.0 Students use strategies, skills, and concepts in finding solutions: 1.1 Use estimation to verify the reasonableness of calculated results. 1.2 2.2 Apply strategies and results from simpler problems to more complex problems. 1.3 Use a variety of methods, such as words, numbers, symbols, charts, graphs, tables, diagrams, and models, to explain mathematical reasoning. 2.5 Indicate the relative advantages of exact and approximate solutions to problems and give answers to a specified degree of accuracy. 3.0 Students move beyond a particular problem by generalizing to other situations: 3.1 Evaluate the reasonableness of the solution in the context of the original situation. 3.2 Note the method of deriving the solution and demonstrate a conceptual understanding of the derivation by solving similar problems. 3.3 Develop generalizations of the results obtained and apply them in other © 2012 Fresno Community Science Workshop. All Rights Reserved worldwide. When linking to or using FCSW content, images, or videos, credit MUST be included. circumstances. © 2012 Fresno Community Science Workshop. All Rights Reserved worldwide. When linking to or using FCSW content, images, or videos, credit MUST be included.