Top Ten Physics Questions and Answers
Top Ten Science Questions: Physics
Physics is seen as the most difficult of the sciences; my pupils usually greet a new physics module with a groan and "I can't do physics!" Not the greatest atmosphere for learning...
Physics deals with the laws of the universe and time - it ranges from how subatomic particles interact to form atoms, to how these atoms form some of the largest phenomena in the universe: planets, stars and galaxies. But physics plays a huge role in our everyday lives too: mobile phones, wi-fi, electricity, jet engines, gravity and magnetism all fall into the eclectic realm that is physics.
This hub looks at questions asked of me in a year of teaching physics - the questions have come from young and old alike, so there should be something of interest for you here. Hopefully the information here can overturn the image that physics is 'too hard' and 'boring' and instead reveal some of the wonderful mystery of our universe.
(BTW - the Northern Lights occur when charged particles from solar wind slam into the Earth's magnetic field. This creates the dazzling, dancing display that is snapped above.)
1. Why do Boomerangs Come Back?
Boomerangs work on the same principles of aerodynamics as any other flying object; the key to how a boomerang works is the airfoil.
An airfoil is flat on one side but curved on the other with one edge thicker than the other - this subjects the boomerang to lift, keeping it in the air. The lift is generated because the air flowing up over the curve of the wing has further to travel than the air flowing past the flat side. The air moving over the curve travels faster in order to reach the other side of the wing, creating lift.
A boomerang has two airfoils, each facing in a different direction. This makes the aerodyamic forces acting on a thrown boomerang uneven. The section of the boomerang moving in the same direction as the direction of forward motion moves faster than the section moving in the opposite direction. Just like tank tracks moving at different speeds, this causes the boomerang to turn in the air and return to the thrower.
Fast Fact: Most original boomerangs don't come back, and are not intended to do so! The returning variety are thought to have been made to scare birds into hunters nets.
2. When does the Sky become Space?
The official boundary between the Earth's atmosphere (sky) and space is called the Kármán line. This line lies 100km above sea level and is named after aeronautical scientist Theodore von Kármán.
Aircraft generate lift due to the flow of air over their wings; the air thins with increasing altitude meaning aircraft must move faster to remain airborne. von Kármán calculated that at 100km, it was more efficient for vehicles to orbit the Earth than to fly. Above 100km, aircraft would have to move faster than satellites orbiting the Earth to generate sufficient lift to stay airborne.
Fast Fact: The highest skydive in history was from 31,300m made by Joseph Kittinger - still well inside our atmosphere.
3. What is Wi-Fi?
The wireless age has dawned, and Wi-Fi is at the heart of it. Wi-Fi is a wireless network which uses radio frequencies instead of cables to transmit data.
A wireless network in not truly wireless as it is built around a source computer connected to the internet via an Ethernet cable. This computer has a router that changes data into a radio signal that can be picked up by an antenna inside your wireless device. To prevent outside interference, the router uses a precise frequency band - just like a walkie-talkie.
When you try to browse the internet using your laptop, an adaptor within the machine communicates with the router via radio signals. The router decodes the signals and fetches the relevant data from the internet through the wired Ethernet connection. This information is converted into radio signals and beamed to the laptop's wireless adaptor. The laptop then decodes this message and (hopefully) shows you the page you googled!
Fast Fact: Wi-Fi does not actually stand for anything. It is a play on the term Hi-Fi. Many people believe Wi-Fi is short for 'Wireless Fidelity' (what does that even mean?)
4. What is Electricity?
Electricity is the flow of any particle with a charge - in the case of our household supply, it is the flow of negatively charged particles called electrons (hence electricity).
In a simple circuit, the electrons are provided by the metal in the wires (usually copper). The battery provides a potential difference (voltage) that provides the 'push' to move electrons towards the positive terminal.
There are two types of electrical current available: Alternating Current and Direct Current. The electical current that comes out of your plug sockets is the former. The National grid provides electricity that reverses direction 50 times per second (50Hz) in the UK. You can actually prove this with a slow motion camera - alternating current explains why lights seem to flicker under slo-mo.
Fast Fact: A current of just 0.1 - 0.2 amps is sufficient to kill a person.
5. What is Radioactivity?
Radioactivity involves the spontaneous decomposition of an unstable atomic nucleus into a more stable form, in one of three decays: alpha, beta, gamma. The nucleus becomes more stable by releasing excess energy either in the form of particles (alpha and beta) or as a wave.
Fast Fact: Lead is the heaviest stable element in the periodic table. All heavier elements decay over time.
6. What is the Sound Barrier?
The sound barrier is broken by any vehicle exceeding the speed of sound: 660mph
Once thought to be an impossible speed, Chuck Yeager broke the sound barrier with the Bell X-1 rocket plant in 1947. As an object moves through the air, it pushes nearby air molecules causing a domino-effect on surrounding molecules. This causes a pressure wave that can be interpreted as 'sound.' As a plane approaches the speed of sound, its pressure waves stack up ahead of it to form a massive area of pressurized air that we call a shock wave.
These shock waves are heard as sonic booms.
Fast Fact: Felix Baumgartner is planning a skydive from 36,500m - he will fall so fast he will become the first person to break the sound barrier without mechanical help.
7. How long could you survive in Space without a Spacesuit?
Contrary to popular belief, and numerous Hollywood movies, you could survive unprotected in space for over a minute - provided you could get back to medical care immediately after. There are one or two things you need to think about if you found yourself in this situation:
- Breathe out: Just like an ascending scuba diver, if you hold your breath, the gas expanding in your lungs due to reduced pressure would cause them to rupture.
- Stay out of the sun: without protection, serious sunburn can ensue.
- You are going to swell up: In the vacuum of space, your body fluids will vaporise, causing tissues to swell up.
- You have ten seconds: Of useful consciousness that is. Due to oxygen depletion, you will also start to lose your vision after this time
NASA has limited experience of this phenomenon, but experience from training accidents suggests that injuries can be reversed. if astronauts are returned into a pressurized oxygen environment within 90 seconds.
Fast Fact: 2001: A Space Odyssey is one of the few films to deal with vacuum exposure correctly. The film's human protagonist, Dave, jumps out of a space pod to re-enter his spacecraft. At no point does his head explode.
8. What is Temperature?
Temperature is a measure of how hot an object is...but what does that mean?
All atoms have kinetic (movement) energy because all atoms move. Even the atoms in a solid vibrate around a fixed spot. How hot an object is reflects the amount of kinetic energy in its molecules.
You cool an object down by removing some of this kinetic energy. Eventually, you will get to a point where the atoms are not moving at all - this is the lowest theoretical temperature and is called 'Absolute Zero.' This theoretical temperature stands at 0K, or -273.15°C (-459.67°F).
Fast Fact: While the temperature of the Southern Ocean stands between -2°C and 10°C, it contains much more heat energy than a boiling kettle. This is because there are many more water molecules in the ocean; even though their individual kinetic energies are lower than those in a kettle, when taken together the overall energy is much higher.
9. What is Gravity?
Gravity is one of the four fundamental forces that apply in our universe:
- Weak Nuclear Force
- Strong Nuclear Force
Gravity is the force exerted by anything that has mass. Even sub-atomic particles exert a gravitational pull on nearby objects. Isaac Newton proved that objects with a greater mass exert a stronger gravitational pull. Weirdly, however, gravity is pathetically weak!
"Weak!? But gravity holds planets in orbit around the Sun, and holds us on the Earth's surface" Correct, but look at it this way - a tiny magnet can hold a paperclip against the gravitational pull of our planet. A newborn baby can defeat Earth's gravity by lifting a block off the floor.
Gravity has undergone some modifications since Newton, with Einstein's General Relativity providing an explanation of how gravity worked. Here is a helpful (although flawed) analogy:
- Space and time form a 2-D fabric analogous to a trampoline.
- Stars, and other objects of great mass, are like bowling balls sitting on the trampoline.
- Roll a ball bearing too close to the bowling ball and it will curve around it like a ball in a roulette wheel - this is a smaller mass being caught by the gravity of a greater mass.
Einstein stated that objects of mass bend and warp the fabric of space-time (bowling ball on trampoline). Large masses move in response to this curvature in space time; move too close to the curve and you are forced to move in a new direction. Matter tells space how to curve; curved space tells matter how to move. Gravity is thus the result of all the collective wrinkles in the fabric of the Universe.
Fast Fact: Even on Earth, gravity is not even. The Earth is not a perfect sphere, and its mass is distributed unevenly. This means that the strength of gravity can change slightly from place to place.
10. How do Magnets Work?
Magnetism is a property of materials that makes them experience a force in a magnetic field. But what makes a metal magnetic? It is all down to unpaired electrons: moving electrons create magnetism due to their magnetic charge, but in most atoms electrons are paired and so cancel each other out.
Most people know the basics of magnets:
- All magnets have two poles - North and South.
- Like poles repel, opposite poles attract.
- Surrounding every magnet is an area that will exert a force: the magnetic field.
- The closer together the magnetic field lines, the stronger the magnet.
What most people don't know is how this works. Unlike poles attract because the magnetic forces are moving in the same direction. Like poles repel because the forces are moving in opposite directions. Think two people trying to push a revolving door:if you push a door while someone pushes from the other side, the door wont move. If you both push in the same direction the door will swing round.
Fast Fact: The only definitive way to determine if a metal is a magnet instead of just magnetic is to see if it can repel a known magnet.
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