--- title: Keeping cold: fridges, freezers and heat pumps — a lesson of Mova's school · trees and pragmatics description: «Keeping cold: fridges, freezers and heat pumps», a lesson of the technology course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: A fridge does not make cold: it moves heat out of the box and lets it go from pipes at the back, which is why the back o --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [Technology](https://md.mova.elamur.ai/free/en/corpora/school/technology/) / Keeping cold: fridges, freezers and he… # Keeping cold: fridges, freezers and heat pumps Lesson 10 of the technology course of Mova's primary school: 18 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: [the lesson at school](https://md.mova.elamur.ai/free/en/school-run/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/0/) — A fridge does not make cold: it moves heat out of the box and lets it go from pipes at the back, which is why the back of a fridge feels warm. - [1](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/1/) — A pump called the compressor pushes a special liquid round pipes; inside the fridge it turns into a gas and soaks up heat, the way drying sweat cools your skin, and outside it gives the heat away. - [2](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/2/) — The humming you hear in the kitchen is the compressor switching on, and the quiet is it resting when the inside is cold enough. - [3](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/3/) — Cold matters because germs grow slowly below about 5 degrees and stop growing in a freezer at about minus 18, so milk and meat keep much longer. - [5](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/5/) — A fridge moves heat out rather than making cold: a special liquid turns to gas in pipes inside and soaks up heat, and the heat is let out from pipes at the back. - [6](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/6/) — The humming noise is the compressor, a small pump, switching on and off to keep the inside cold; a fridge is one of the few machines in a house that runs day and night. - [7](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/7/) — A freezer works like a fridge but colder, around minus 18 degrees, so germs stop growing and food keeps for months. - [8](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/8/) — Freezing does not kill most germs; they wake up again when the food thaws. - [9](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/9/) — A small switch turns on the fridge light when the door opens and off when it shuts, and a rubber seal with magnets inside keeps the cold in; a piece of paper shut in the door should be hard to pull out. - [10](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/10/) — Food stays safer in a fridge kept below about 5 degrees, because germs grow slowly in the cold, so leftovers go in once they have cooled. - [11](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/11/) — Each time the door is open, cold air spills out at the bottom, so the door should not be left open; an open fridge cannot cool the kitchen, because it works harder and lets out even more heat at the back, so the room gets warmer. - [12](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/12/) — Water gets bigger when it freezes, which is why a full glass bottle can crack in the freezer. - [13](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/13/) — Rules: never climb inside a fridge or freezer, because you could get trapped, and never put ice or metal straight from the freezer on your lips or tongue, because it can stick and hurt. - [14](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/14/) — A cool box has thick foam walls, mostly trapped still air, which slow heat getting in, and its ice packs soak up heat as they melt. - [15](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/15/) — An air conditioner works like a fridge for a room, taking heat from inside and pushing it out through a box outside; the first modern one was built in 1902 to stop paper wrinkling in a print shop. - [16](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/16/) — Air conditioners drip water outside because cooling the air turns some of its water vapour (water as an invisible gas in the air) into droplets. - [17](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/17/) — A heat pump works like a fridge backwards: it collects heat from the outside air or the ground, even in winter, because even cold air holds some heat, and pumps it into the house. - [18](https://md.mova.elamur.ai/free/en/corpora/school/technology/10-keeping-cold-fridges-freezers-and-heat-pumps/18/) — Open supermarket chillers blow a curtain of cold air down the front to keep most of the cold in, and adding doors to them saves a lot of electricity. - ← previous: [Phones and computer chips](https://md.mova.elamur.ai/free/en/corpora/school/technology/9-phones-and-computer-chips/) - next →: [Cooking machines: oven, microwave, kettle, toaster and hob](https://md.mova.elamur.ai/free/en/corpora/school/technology/11-cooking-machines/) - ↑ back to [Technology](https://md.mova.elamur.ai/free/en/corpora/school/technology/)