Hooke's law describes how springs respond to having forces applied. This experiment allows you to apply force using weights and measure how springs of different stiffness extend in response. You can calculate the stored elastic potential energy in the springs and even go to different parts of the Solar System to see how changing the strength of gravity changes the weight applied to the springs!
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Stretching – the truth!
You may wonder why we study springs and why questions about stretching springs appear on exams. Sure, springs are used in the world, but are they really so important? Why is it important to know how springs stretch when they are pulled?
Well, first, springs are incredibly useful. When made from elastic materials, such as most metals, springs stretch when pulled and return to their original size when released. They can also be compressed and, again, return to their original size when released. The stretching or compression stores energy that is then returned when the spring is released. This energy storage and return is the key reason springs are useful. Springs use this capability in all sorts of applications, including in high tech areas such as automotive, industrial tools and robotics, to more everyday items such as trampolines, mattresses, children’s play equipment, door handles and retractable pens.
The second reason is that the way that springs respond to force being applied to them (i.e. being pulled or mass added to one end of them) is identical to how materials in general behave. If materials are pulled, then they stretch. The coiled shape of a spring, though, means that the ends tend to move large distances compared to a regular shape of the same material (e.g. a simple rod). This means that studying what happens to springs when they are pulled allows simple measurements to be performed that give us understanding of how all materials behave when they are pulled. Materials behave this way in any application where they have force applied to them, e.g. in construction, vehicles, heart valves, body implants, plants, rocks, furniture, tools, footwear – the list goes on and on. And don’t forget this includes your body too!
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Download the file below for the quick guide for the Hooke's Law experiment (requires login) or follow these brief instructions:
5. To change to a different part of the Solar System:
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Specific heat capacity of solids is important to understand in lots of applications that deal with heat energy and changes in temperature. This experiment allows you to control the electrical heating power applied to a choice of six different materials and measure the rate at which the sample temperature changes. You can then calculate the specific heat capacity of the chosen material. Compare the different materials, investigate the effect of having thermally insulated or uninsulated samples, and see if different heating powers change the measurements.
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There are lots of ways that we use materials that see them change temperature. Some examples include heating systems in buildings (especially storage heaters), simple household appliances such as an iron or an oven, combustion engines in cars, jet engines in aircraft, high speed machines such as drills, and industrial furnaces; however, examples also include applications where the temperature is reduced, for example in refrigerators, freezers and heat sinks, which are used to help cool another component.
A change in a material’s temperature will also result in a change in its heat energy. Different materials, however, will have a different change in heat energy for a given change in temperature.
The material's property we use to show this difference is called specific heat capacity. This property is key to allowing us to understand how components will perform in thermal applications and help us to choose the most appropriate material. If you go to study Physics or Engineering at university you will probably also learn how specific heat capacity values depend on a material’s types of atom, atomic bonding and electrical properties.
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Heat is transmitted by conduction, convection or radiation. This experimental allows you to investigate thermal conduction by measuring the time for thermal energy to pass through different materials.
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The thermal conductivity of materials is hugely important for how we live today.
Thermally-insulating materials are found in lots of places around the home. This includes safety items such as oven gloves or fire blankets and inside ovens and refrigerators to stop them heating or cooling the rest of your kitchen! Your hot water pipes and water heating system will probably have thermal insulation around them to stop unwanted heat loss. Houses and other buildings usually have thermal insulation around them to reduce heat loss when it is cold outside and reduce heat entering when it is very hot outside. This is important as we try to reduce CO2 emissions from energy use as part of our fight against climate change. Insulating materials are also used around industrial furnaces, in refrigerated vehicles and packages (e.g. for transporting food or medical supplies) in aircraft to keep crew and passengers warm in the cold air, and in spacecraft to stop the insides reaching temperature extremes and protecting the spacecraft itself from burning up if it re-enters Earth’s atmosphere.
Thermally-conducting materials are also very important to heating and cooling systems, such as heating elements in kettles and furnaces, radiators, high speed industrial machines and heat-sinks found in electronic devices.
Heat conduction is also really important in many renewable energy technologies, such as solar cells (photovoltaics), which work less efficiently if they heat up, and ‘thermoelectric generators’ (TEGs), which are most efficient if they conduct electricity well but conduct temperature weakly.
This huge range of applications means there is a lot of research and development of materials with new thermal conduction properties. How materials conduct heat is also related to their atomic-scale structure – this means that we can learn about the materials from how they conduct heat and change their structure in order to create new properties that are better suited for particular applications.
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Download the file below for the background science behind the Thermal Insulation experiment (requires log in).
This experiment allows you to measure the infrared emission from the four different surfaces of a Leslie cube. You can choose which surface to measure, see what happens as temperature changes, and adjust the signal strength by changing the detector position and the level of signal amplification. Advanced activities involve calculations of emissivity, how signal varies with source-detector separation, and the temperature-dependence of infrared emission.
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Any object emits electromagnetic radiation due to having a temperature above absolute zero (about -273.15°C), although different surfaces emit the radiation to different levels. This might seem like a curiosity created just for lab measurements but it has lots of real-world relevance.
The hotter an object is, the stronger this thermal emission is. Objects with different temperatures emit different parts of the electromagnetic spectrum too. Objects close to room temperature (like us!) only emit infrared radiation (‘IR radiation’), which we feel as warmth. Objects at hundreds of degrees Celsius start to emit visible radiation (wavelength from 400 – 700 nm), those at thousands of degrees Celsius emit ultra-violet (UV) radiation (wavelength from 100 – 400 nm), while the hottest objects in the galaxy (e.g. regions around black holes) emit X-ray radiation (wavelengths shorter than 100 nm).
The most important aspect of thermal emission is that life on our planet would not exist without it! Our nearest star, the Sun, is so hot its IR emission reaches across over 140 million kilometres (that’s over 90 million miles) of space to warm our planet. The Sun’s visible light also allows us to see. The Earth’s ozone layer plays an important role in absorbing most of the UV light from the Sun, which would otherwise reach us at harmful levels.
Astronomers also use the thermal emission from other stars and astronomical objects to learn about how they were formed, their lifecycle, and the processes that go on within them.
Climatologists and meteorologists (scientists who study the Earth’s climate and weather) use satellites to map the IR emission of the Earth’s atmosphere and land to help predict future weather events and trends. The surface of the Earth can also be imaged to locate underground heat sources, objects and water flows.
In smaller-scale applications, surface materials are often chosen to help either cool or insulate an object by either maximising or minimising IR emission, depending on what is needed. IR emission is used in some household or industrial heaters and to measure temperature in areas such as industrial manufacturing processes and medical applications, e.g. measuring the temperature of a patient.
‘Thermal imaging’ cameras create images from IR emission for a huge range of applications, including night vision (e.g. for security systems or non-invasive imaging of wild animals), analysing heat sources in electronic circuits, industrial monitoring (e.g. web servers, aircraft engines), and analysing the thermal efficiency of objects from miniature devices to houses.
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Download the file below for the quick guide for the Leslie Cube (IR emission) experiment (requires login).
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Download the files below for activities and associated worksheets for the Leslie Cube (IR emission) experiment (requires login).
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Download the file below for the background science behind the Leslie Cube (IR emission) experiment (requires log in).