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Speed limits
The back pages Almost the last word Did this T. rex sound more like a screeching bird than a roaring lion?
Speed limits The most powerful cars intended for road use tend to have a top speed that ranges between 300 and 350 kilometres per hour. Is this due to some physical limitation or just practicality of design because you will never be able to reach these speeds let alone go faster on public roads?
Mike Clarke Castle Hedingham, Essex, UK It is both difficult and expensive to design tyres capable of speeds over 300 kilometres per hour. Even tyres designed for these speeds need to be in “as new” condition to operate safely. After only a few weeks of use at normal speeds, they probably wouldn’t be safe to use at high speeds. A further limitation is the driver. At 300 kilometres per hour, you are travelling more than 80 metres per second, but human reaction times vary between about 0.7 and 3 seconds. That means anything 100 metres ahead of you on the road, such as debris, would be almost impossible to react to. 54 | New Scientist | 1 June 2019
UNIVERSAL PICTURES
Gordon Drennan Adelaide, South Australia The amount of power it takes a car to go faster goes up exponentially. To double a car’s top speed, its engine must be eight times as powerful. Aerodynamic lift over the body also increases exponentially. At the same time, the traction of the tyres has to be better to deliver the higher power required to the road. Such cars consequently cost a lot more, and as a result, there are far fewer people who can afford to pay for them and who see any point in having such a car. The fastest road-legal car currently on the market is the Koenigsegg Jesko, which is expected to have a top speed of 483 kilometres per hour – and would cost around A$6.5 million here in Australia, if it weren’t already sold out. But there is no fundamental reason why a road car couldn’t go faster.
dry food on the inside without showing any signs on the outside.
This week’s questions When a Tyrannosaurus rex or other carnivorous dinosaur is depicted on screen, it roars like a carnivorous mammal. But birds developed from dinosaurs, so could they have screeched or called like the modern cassowary, or made no noise at all? Andrew Johnson, Banbury, Oxfordshire, UK When I drain a can of chickpeas, the liquid forms a soapy foam. What causes this, and if it is related to soap, could it be used as an eco-friendly replacement? John Munroe, Edinburgh, UK
Stephen Johnson Eugene, Oregon, US A powerful car whose top speed isn’t restricted by an onboard computer eventually reaches a speed where the vehicle can’t compress any more wind in front of itself. This compression goes up with the square of speed, so that each doubling of speed requires four times as much energy to overcome this effect. In addition, there is drag at the rear of the car from the induced vacuum. A final limit of sorts on speed is the strength of the suspension system of the car. To prevent highspeed cars from trying to fly as the wind speed under the vehicle increases, spoilers are employed at the rear of the car and air dams at the front. These increase downward force to the point where the effective weight of a moving car on the road can more than double. In a tunnel of the right shape, it would be possible to drive such a car upside down, as it would effectively stick to the road with a force greater than its weight.
Toast, not toast Heating bread in a toaster and a microwave oven creates very different results. What do microwaves do to bread?
Isabella Van Damme Arborfield, Berkshire, UK The results are different because microwaves heat bread from the inside, while a toaster heats from the outside. In a toaster, the bread’s surface quickly reaches temperatures at which the Maillard reaction causes browning and a toasted flavour. Excessive heating can lead to carbonisation or burning. In contrast, heating a slice of bread in a microwave will dry it out without achieving the surface temperatures required for the browning reactions. Excessive microwave heating can “burn”
Parvez M. Ashraf Dhaka, Bangladesh As well as heating only the surface of the bread, using a toaster causes the bread to lose moisture, making it dry and crispy. In microwave heating, the starch of the bread is re-gelatinised. That is to say, the starch molecules bind to water molecules, which sort of dissolve or plasticise the starch, making the texture of the bread softer overall. Maria Tsikkinis London, UK One of the properties of microwaves is that they are absorbed by water. When bread is irradiated with microwaves, the water in the bread heats up and conducts the heat to the surrounding food. When the water molecules absorb enough energy, they evaporate, which is why the bread is steaming when you remove it from the microwave and why the slice, soft when you take it out, quickly becomes rock hard once it cools down. A toaster, on the other hand, uses infrared radiation. These are heat waves and their energy is absorbed by the whole of the bread, rather than just the water. Theo Megarrity, Brisbane, Australia “Toasting” toast in the microwave is like trying to start a fire with a pot of boiling water. Microwaves cook through radiation (emitting waves), and toasters cook through proximity to hot elements, which results in the crispy delight that is toast.
Want to send us a question or answer?
Email us at [email protected] Questions should be about everyday science phenomena Full terms and conditions at newscientist.com/lw-terms
Speed limits The most powerful cars intended for road use tend to have a top speed that ranges between 300 and 350 kilometres per hour. Is this due to some physical limitation or just practicality of design because you will never be able to reach these speeds let alone go faster on public roads?
Mike Clarke Castle Hedingham, Essex, UK It is both difficult and expensive to design tyres capable of speeds over 300 kilometres per hour. Even tyres designed for these speeds need to be in “as new” condition to operate safely. After only a few weeks of use at normal speeds, they probably wouldn’t be safe to use at high speeds. A further limitation is the driver. At 300 kilometres per hour, you are travelling more than 80 metres per second, but human reaction times vary between about 0.7 and 3 seconds. That means anything 100 metres ahead of you on the road, such as debris, would be almost impossible to react to. 54 | New Scientist | 1 June 2019
UNIVERSAL PICTURES
Gordon Drennan Adelaide, South Australia The amount of power it takes a car to go faster goes up exponentially. To double a car’s top speed, its engine must be eight times as powerful. Aerodynamic lift over the body also increases exponentially. At the same time, the traction of the tyres has to be better to deliver the higher power required to the road. Such cars consequently cost a lot more, and as a result, there are far fewer people who can afford to pay for them and who see any point in having such a car. The fastest road-legal car currently on the market is the Koenigsegg Jesko, which is expected to have a top speed of 483 kilometres per hour – and would cost around A$6.5 million here in Australia, if it weren’t already sold out. But there is no fundamental reason why a road car couldn’t go faster.
dry food on the inside without showing any signs on the outside.
This week’s questions When a Tyrannosaurus rex or other carnivorous dinosaur is depicted on screen, it roars like a carnivorous mammal. But birds developed from dinosaurs, so could they have screeched or called like the modern cassowary, or made no noise at all? Andrew Johnson, Banbury, Oxfordshire, UK When I drain a can of chickpeas, the liquid forms a soapy foam. What causes this, and if it is related to soap, could it be used as an eco-friendly replacement? John Munroe, Edinburgh, UK
Stephen Johnson Eugene, Oregon, US A powerful car whose top speed isn’t restricted by an onboard computer eventually reaches a speed where the vehicle can’t compress any more wind in front of itself. This compression goes up with the square of speed, so that each doubling of speed requires four times as much energy to overcome this effect. In addition, there is drag at the rear of the car from the induced vacuum. A final limit of sorts on speed is the strength of the suspension system of the car. To prevent highspeed cars from trying to fly as the wind speed under the vehicle increases, spoilers are employed at the rear of the car and air dams at the front. These increase downward force to the point where the effective weight of a moving car on the road can more than double. In a tunnel of the right shape, it would be possible to drive such a car upside down, as it would effectively stick to the road with a force greater than its weight.
Toast, not toast Heating bread in a toaster and a microwave oven creates very different results. What do microwaves do to bread?
Isabella Van Damme Arborfield, Berkshire, UK The results are different because microwaves heat bread from the inside, while a toaster heats from the outside. In a toaster, the bread’s surface quickly reaches temperatures at which the Maillard reaction causes browning and a toasted flavour. Excessive heating can lead to carbonisation or burning. In contrast, heating a slice of bread in a microwave will dry it out without achieving the surface temperatures required for the browning reactions. Excessive microwave heating can “burn”
Parvez M. Ashraf Dhaka, Bangladesh As well as heating only the surface of the bread, using a toaster causes the bread to lose moisture, making it dry and crispy. In microwave heating, the starch of the bread is re-gelatinised. That is to say, the starch molecules bind to water molecules, which sort of dissolve or plasticise the starch, making the texture of the bread softer overall. Maria Tsikkinis London, UK One of the properties of microwaves is that they are absorbed by water. When bread is irradiated with microwaves, the water in the bread heats up and conducts the heat to the surrounding food. When the water molecules absorb enough energy, they evaporate, which is why the bread is steaming when you remove it from the microwave and why the slice, soft when you take it out, quickly becomes rock hard once it cools down. A toaster, on the other hand, uses infrared radiation. These are heat waves and their energy is absorbed by the whole of the bread, rather than just the water. Theo Megarrity, Brisbane, Australia “Toasting” toast in the microwave is like trying to start a fire with a pot of boiling water. Microwaves cook through radiation (emitting waves), and toasters cook through proximity to hot elements, which results in the crispy delight that is toast.
Want to send us a question or answer?
Email us at [email protected] Questions should be about everyday science phenomena Full terms and conditions at newscientist.com/lw-terms