What's a positive feedback loop

Stage in which a star’s outer layers have started to cool and grow outward?

Is a pencil falling to the floor anon contact force, a force, or a contact force

Large helium-filled balloons are used to lift scientific equipment to high altitudes. what is the pressure inside such a balloon if it starts out at sea level with a temperature of 10.0ºc and rises to an altitude where its volume is twenty times the original volume and its temperature is – 50.0ºc ?