Why do we need the first law of thermodynamics? What use is it? Dr Suzie Sheehy explains what it means to a particle physicist. Day 9 of our advent calendar. Watch all the videos here: http://www.rigb.org/christmas-lectures/supercharged-fuelling-the-future/thermodynamics-2016-advent-calendar?utm_source=youtube&utm_medium=social&utm_campaign=201612_channel_advent The four laws of thermodynamics touch almost every type of science, and impact on research and understanding in different ways. In this animation, particle accelerator physicist Suzie Sheehydiscusses why the first law of thermodynamics is so important to particle physics. To describe the motion of almost any system, from a car on a road to particles in an accelerator, you have to be able to trust that certain quantities are conserved. From the simple rule that energy is conserved, you can deduct incredible information. In a particle accelerator, particles are collided with each other, or with other matter. The result is a spray of the component particles, but some of these can’t be detected by modern machines. For example, neutrinos have almost no mass and as such are almost impossible to directly detect. But because energy is always conserved, the physicists can tell what properties they haven’t detected by calculating the difference between the initial input and the output they find. The first law of thermodynamics gives a predictive power that lets scientists understand the world. This video was supported by the Science and Technology Facilities Council. The 2016 advent calendar explores the four laws of thermodynamics with a new short film each day, with explosive demonstrations, unique animations, and even a musical number. Open the calendar at http://www.rigb.org/christmas-lectures/supercharged-fuelling-the-future/thermodynamics-2016-advent-calendar?utm_source=youtube&utm_medium=social&utm_campaign=201612_channel_advent Subscribe for regular science videos: http://bit.ly/RiSubscRi