Topic Area(s) Cost Time Grade Level Supplies. minutes. or plate Friction. Hot glue gun Fluid mechanics. or tape Motion

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1 Balloon Hovercrafts Topic Area(s) Cost Time Grade Level Supplies Force balance $.50 / kit CD, cardstock Properties of air minutes or plate Friction Hot glue gun Fluid mechanics or tape Motion Pop-top lid from drink bottle or soap bottle Balloon Curriculum Links Current curriculum Grade 6 Processes of Science: o Manipulate and control a number of variables in an experiment o Apply solutions to a technical problem (e.g., malfunctioning electrical circuit) Grade 7 Processes of Science: create models that help to explain scientific concepts and hypotheses New curriculum (based on latest online version August 2015): 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

2 Materials (for class of 30, working in pairs) 15x Balloons 15x Plates, CDs or cardstock 15x Pop-top lid from drink bottle or soap bottle collect these from your recycling until you have enough Tape or glue gun Surfaces to test on (smooth table or floor) Background Information Newton s Laws of Motion Newton s laws of motion are three physical laws that describe the relationship between a body, the forces acting upon it and its motion in response to those forces. When forces acting on an object are in equilibrium (i.e. the forces are balanced), the object will remain either stationary or continue to move at a constant velocity. This is also known as the law of inertia or the first law where a body continues to do whatever it happens to be doing unless a force is exerted upon it. Movement will occur in the direction of the net force (the total force acting on the object when all the individual forces are added). The force on an object is equal to the mass of the object multiplied by the acceleration of the body. This is Newton s second law. F = ma Newton s third law states that for every action (force) there is an equal and opposite reaction. For example, this law is seen when a person walks: they push against the floor and the floor pushes against the person. Friction Friction is the force that resists the relative motion of two surfaces sliding against each other. The force of friction (Ff) is dependent on the coefficient of friction (µ) of the two surfaces and the normal force (Fn) exerted by each surface on the other. In the simple case of a mass resting on a surface, the only component of the normal force is the force due to gravity. F f μf n Figure 1: Free body diagram for a block on a ramp by Krishnavadela (CC0 1.0) via Wikipedia

3 Air Cushion Hovercrafts glide over smooth surfaces by hovering upon an air cushion. An air cushion is made by currents of low pressure air that are pushed downward against the surface below the hovercraft. The currents are trapped below the hovercraft with a skirt. These trapped currents current the air cushion that allows the hovercraft to glide on smooth surfaces. Figure 2: Hovercraft: 1) propellers, 2) air currents, 3) fan, 4) flexible skirt by MesserWoland (CC-BY-SA-3.0) via Wikipedia Procedures 1) Glue or tape the pop-top lid to the CD, making sure that the hole in the cap and CD are aligned. 2) Ensure the pop-top lid is closed. 3) Blow up the balloon and pinch it so no air escapes do not tie it off. 4) While pinching the balloon, stretch the mouth of the balloon over the bottle cap. 5) Place the hovercraft on a hard, smooth surface, open the pop-top lid and nudge it along. Extensions: Drag the hovercraft along the testing surface with the balloon deflated. Why is it easier to move when the balloon is inflated? Try using your hovercraft on a number of different surfaces to investigate where it works best. How can you alter the hovercraft to make it hover for longer? Try using alternate materials (cardstock or plates) or different sizes of balloons. Have students measure variables (distance travelled, time hovering, balloon size, weight, etc.), enter into a table or graph and interpret. Want a bigger project? Build a hovercraft with a leaf blower for students to try sitting on:

4 What Happened? Before you release the air from the balloon, the hovercraft is at rest. The air inside the balloon is exerting pressure evenly against the balloon walls. When you release the mouth of the balloon, air is forced out of the balloon. This creates air currents beneath the hovercraft. This creates an opposite force upwards which lifts the hovercraft off the group, explained by Newton s third law of motion. This air cushion also helps the hovercraft move by reducing the amount of friction between the hovercraft and the ground. Figure 3: Free body diagrams of the forces of the hovercraft and ground

5 Connecting Engineering to Your Classroom Hovercrafts are crafts capable of travelling over land, water, mud or ice and other surfaces. They are used throughout the world as specialized transports in disaster relief, coastguard, military and survey applications. Very large versions have been used to transport hundreds of people across the English Channel, others have been used to transport large equipment in hostile environments and terrain. The Richmond Coast Guard station has three hovercrafts they can often be toured at Richmond s Ships to Shore event ( and other community events. Friction is an important consideration for engineers who design moving objects. Sometimes they design materials to increase the friction and other times to reduce the friction. Snow tires may have metal studs that poke into the snow and ice, creating more friction than rubber alone. Rollerblade wheels must be sticky enough for control, but not so soft that they create too much drag or wear out too fast. Engineers also reduce friction between moving parts so that they run smoothly and do not wear down as quickly.