6. When kept at the same temperature, a metal block will feel colder than a wooden block. It’s due to the higher thermal conductivity of metal that draws heat away from your hand at a higher rate than the wood, making your hand perceive it to be colder.
Metals are better thermal conductors than any non-metal object because they can more easily transfer or absorb heat. So, when placed with a colder object, it will easily transfer heat, and when kept with warmer objects, it will easily absorb heat.
Our skin cannot detect the actual temperature of any object, but the numerous temperature-sensitive nerve endings of the skin help us to detect and “feel” the difference in temperature. When we touch an object that is colder than our hand, our finger loses heat and therefore feels cold. The opposite happens when we touch a hotter object. Since metals are good conductors of heat, we feel the temperature difference instantly. But non-metal objects, such as plastic and wood, are thermal insulators. They do not transfer heat as easily as metals.
Here are some real-life examples of this phenomenon:
a. When you get out of the shower and step on the carpet, it feels warm, but if you step on tiles, it will feel cold.
b. When you take a cake from the oven, you can touch the cake but not the pan, even though both cake and pan are at the same temperature in the oven. (1, 2)
7. There is gravity in space, but astronauts feel weightlessness in space because they have the same acceleration as the spaceship.
Watching an astronaut appear weightless and float around in the spaceship can make anyone believe that space is devoid of gravity. The truth is gravity exists everywhere, including space. Every object exerts some gravitational force on other objects, however small or big. Gravity is what keeps this universe together. Gravity makes the Moon orbit around the Earth and the planets around the Sun.
Astronauts in a spacecraft or inside the International Space Station appear to be floating due to the speed. Gravity does exist in this scenario. It is the Earth’s gravity that keeps the ISS in its orbit. The effect of Earth’s gravity is such that the ISS is actually falling towards the Earth. As the ISS accelerates towards Earth, the Earth curves away from beneath it, and instead of falling into the Earth, the space station orbits around it. Astronauts inside the ISS have the same acceleration as the space station. That’s why they feel weightless.
If you are still thinking weightlessness can only be achieved where there is zero gravity, then think again. Because momentarily, you can experience weightlessness even on Earth. A person inside an elevator would feel weightless if they are on the top floor and the cable suddenly snapped. Also, while riding in a roller coaster, each time it starts to go down from a height, people in it will feel weightlessness. (1, 2)
8. You are safer inside a car during a lightning storm than outside under a tree, because when struck by lightning, the metal body of the car acts as “Faraday’s cage,” limiting the charge to the external surface, keeping its occupants safe.
Lightning can strike anytime, and believe it or not, it can strike even if there aren’t any clouds overhead. Bolts of Lightning are known to strike more than three miles from the center of the thunderstorm cloud. In such a situation, there is little you can do to save yourself. But what if you are in a park or near a forest and can see the thunderstorm approaching? However tempting it might seem, never stand under a tree during lightning. A tree cannot save you when lightning strikes. The best decision would be to the park the car at the side of the road and just stay in it until the lightning subsides.
It is a widespread belief that the rubber tires of car insulate the car and its occupants from the ground, saving them if lightning strikes. Actually, this is just a myth, even though it is not completely illogical as rubber is a good insulator, the tires cannot stop electricity of such a high-magnitude charge as is present in lightning. What actually saves you is the metal body of the car. The metal roof and body act as a Faraday cage when lightning strikes. The charge disappears into the ground by traveling through the metal body frame. So, it’s important that you don’t lean on the door or touch any other metal part of the car’s body during lightning. (1, 2, 3)
9. The heat generated during re-entry of a spacecraft isn’t (primarily) the result of friction against the atmosphere. It’s caused due to rapid compression of the atmosphere by the spacecraft.
We all know that that a meteor burns up when it enters Earth’s atmosphere. This is due to the extreme heat generated due to friction with Earth’s atmosphere. This can be dangerous when planning for space travel at extremely high speed. So, while planning for space programs, scientists take special precautions to protect the spaceship from heat. So, what causes the atmosphere to heat up while a spacecraft re-enters? The most common answer would be friction. While friction does play a role in a later part, the heat produced just as the spacecraft re-enters is actually due to compressive heating.
During re-entry, the spacecraft arrives at a speed of about 17,000 miles per hour. As the spacecraft enters the atmosphere at such a high speed, it heavily compresses the air in front of it and pushes the air off to the side. This compression raises the air temperature as high as 3,000 degrees Fahrenheit! As the compressed air heats up, the expanding air cools down (according to the Ideal Gas Law). However, this super-hot air doesn’t even touch the surface of the spacecraft. It’s because when the spacecraft enters the atmosphere, the air heats up so much that it forms a shock-wave of plasma around the aircraft. This insulating shock-wave saves the nose and the underside of spacecraft from direct friction caused by the air. Heat moves to the spacecraft from the compressed air through convection and radiation. To protect the crafts from heat, the body of spacecraft are fitted with heat shields such as heat-resistant silica tiles. (1, 2)
10. It is more difficult to shoot a spacecraft to the Sun than to exit the Solar System because the launched spacecraft must accelerate almost equal to Earth’s velocity and in the opposite direction.
The first spacecraft to leave the Solar System was NASA’s robotic Voyager 1 probe. After streaking through space for nearly 35 years, it achieved this feat in August 2012. The next one was NASA’s Voyager 2 which escaped from the Solar System on 5 November 2018. Both these missions are an incredible feat in space travel. But the actual testament of human ingenuity and engineering is reaching the center of our Solar System, i.e. the Sun. NASA had already taken the first step towards it. On 12 August 2018, NASA launched the Parker Solar Probe. The aim is to swoop the probe within four million miles of the Sun’s surface. Since 2018, it has twice encountered the Sun. The third Solar encounter will begin on August 27, 2019.
Believe it or not, sending a spacecraft to the Sun is harder than sending it outside the solar system. A common belief is that since the Sun’s gravity is extremely high since it is what keeps the solar system intact, we can just send a spacecraft to space and let it fall into the sun. As easy as it may seem, it cannot be done, and here is the reason why. To launch a spacecraft towards the Sun, it must accelerate to nearly match the Earth’s velocity, and that, too, in the opposite direction. This will cancel out Earth’s motion, and the spacecraft can surrender to the Sun’s gravity and begin to fall towards it. But we cannot achieve this feat with the current rocket technology. So, how did Parker Solar Probe go to the Sun? Well, it actually got help from the planet Venus and used a slingshot maneuver called “gravity assist.” (1, 2, 3)