Question: How do gases in exible and rigid containers achieve and lose buoyancy? Learning Goals: Students will (on a molecular level) be able to... 1) Determine what causes a helium balloon to rise or sink in the air around it. 2) Explain why a rigid sphere containing helium oats or sinks, 3) Explain why a hot air balloon must have a heater to keep it aloft (oating in air). 4) Describe the differences between how a hot air balloon, rigid sphere, and helium balloon function and why. Directions: . Don't vary the gravity for this activity. ' Use the procedure provided under each learning goal to conduct your investigation. ' Describe in writing your observations as you progress through the steps. After completing the procedure, write in paragraph form an explanation for what you observed based on your knowledge of the kinetic molecular theory and the relationships between gas variables (pressure, volume, temperature, kinetic energy, velocity, and number of gas particles). Refer to your data and observations to support your explanation. Goal 1: Determine what causes a helium balloon surrounded by air to rise or sink. 1. Open the PhET Simulation "Balloons & Buoyancy" . Choose the "Helium Balloon\" setting from the top menu bar. Set the initial conditions to match those shown in the diagram below. \" Hid. Tools 2. Assume that the heavy gas particles represent air particles. Record the initial temperature, pressure gauge reading, and speed (velocity) of these particles. Temperature: Pressure gauge reading: Speed of air particles: 3. Recall that the density of any substance equals its mass + its volume. This is true for gases, too. Gases, like all other matter on Earth, are affected by the downward pull of gravity. When