# Up to the Edge of Space Squeeze, heat, cool and pump a gas cylinder to see how pressure, volume, temperature and moles combine into PV = nRT, then launch a weather balloon that bursts near 33 km\. By Numa Topic: Physics & Chemistry [Open the interactive Jig](https://ask.jig.com/j/b9JpBTr4uwjF) ## Transcript ### 1. Up to the Edge of Space Twice a day, at weather stations around the world, someone lets go of a balloon like this one\. It climbs for about two hours, swells to the width of a house and bursts more than 30 kilometres up\. To find out why, we start with the gas in this glass cylinder\. This station is 2 kilometres up, where the air already presses about a fifth less than at the coast\. ### 2. A gas is particles in motion A gas is tiny particles in mostly empty space, moving in straight lines until they hit something\. Turn on Follow one particle to see its path\. This picture of a gas is the kinetic molecular theory\. Their hits on the walls add up to pressure, measured in kilopascals, or kPa\. Temperature, in kelvin, or K, measures their average energy of motion\. The yellow marks show where particles hit the walls\. A nitrogen molecule in room\-temperature air moves at about 500 metres per second\. ### 3. Squeeze it: Boyle’s law Keep the temperature the same and squeeze the gas into a smaller volume, the space it fills\. Drag the piston handle down from 2 litres to 1 litre and watch the gauge\. What happens to the pressure when the volume halves? Then pull the handle up to give the gas more room\. Robert Boyle measured this in 1662 with a J\-shaped glass tube\. ### 4. Heat it, cool it: Charles’s law Drag the cylinder onto the hot plate, then into the ice bath, and watch the piston\. It slides freely now, so the pressure stays the same\. Gas laws use the kelvin scale, which starts at absolute zero, the coldest anything can be\. 0 °C is 273 K\. Doubling the kelvin temperature doubles the volume\. Doubling degrees Celsius does not\. ### 5. Lock the piston: Gay\-Lussac’s law The clamp now holds the piston, so the volume cannot change\. Drag the hot plate dial round clockwise to heat the gas\. Hotter particles hit the walls harder and more often, so the pressure climbs with the kelvin temperature\. Each reading lands on the graph\. Then press Extend line to see where the pressure reaches zero\. Tyres follow this law: a drive that warms the air from 20 °C to 35 °C raises their pressure about 5 percent, so they are checked cold\. ### 6. Add more gas: Avogadro’s law Push the pump handle all the way down, again and again, to add air, and watch the volume\. Chemists count particles in moles\. One mole is 6\.02 × 10²³ particles\. The clamp is off, so pressure and temperature stay the same, and volume rises in step with moles\. At 0 °C and 101\.3 kPa, one mole of any gas fills 22\.4 litres\. ### 7. All together: PV = nRT The four laws join into one, the ideal gas law: pressure times volume equals moles times R times temperature\. R is a fixed number called the gas constant, 8\.314 when you measure in kPa, litres, moles and kelvin\. Check it with your cylinder's readings: both sides come out the same\. A sealed bag of chips puffs up on a plane because the cabin is kept near 75 kPa\. ### 8. Launch to the edge of space Press Release and watch how much the balloon grows\. It is partly filled with helium and carries a radiosonde, a small box that radios back pressure and temperature\. Higher up, the air presses far less but is only a little colder, so the helium spreads out\. At about 33 km the latex bursts\. A parachute brings the radiosonde down, and its readings go into the next weather forecast\.