# View all Ask-a-Physicist

In general relativity, gravity is described as a distortion of space time. Most vulgarized books use the simplified image of a 2D plane being bent downwards by a mass, so that any matter traveling in the area would have to follow the bending of the plane, which would then explain why things are attracted to one another.

Keeping the same simplified metaphor, could we imagine something that would bend the plane upwards, thus causing objects to be repelled? Would such a thing be considered to have negative mass? Is the concept theoretically possible?

Find out the answer »

My friend and I are having a debate on wind turbines or anything that travels in a circular motion. One of us says that the very tip of the turbine blade is traveling faster than the inner part that is close to the axis. We both agree that it has the same rpm, but what part travels at a faster mph?
Find out the answer »

If you had a light in a room which was entirely sealed with mirrors, then switched the light off, would the room stay lit?

Would the light just keep reflecting off the mirrors?

Would it slow down? Perhaps to the point where it is no longer visible?

Find out the answer »

I understand what happens and why, when I drop a tennis ball that is resting on top of a basketball. What I am trying to figure out is, why do I not get the same results with a ping pong ball on top of a basket ball. Any ideas?

Find out the answer »

It looks like they are looking for positive mass particles at the LHC at CERN. Isn't it logical that there are negative-mass "anti-particles"? Does the LHC have the capability of measuring negative mass?

Find out the answer »

If a person stepped on a home bathroom scale, and weighed 170 lbs, he would weigh a different weight on this same scale when on other planets due to the force of gravity.

If, however, a person stepped on a professional medical scale — the kind with weights attached that you slide (as opposed to a bathroom scale) and weighed 170 pounds on Earth, would the weight of the person be the same on the other planets as it is on Earth (170 lbs)? This has become a bone of contention in an otherwise ideal marriage.

Find out the answer »

Is there a particular range of frequencies at which parts of the human body (or the human body overall) normally vibrates? Because in an episode of the sci-fi TV series Fringe, they claimed that they could figure out if one character was from this universe or a parallel universe by measuring the frequency at which he was vibrating.

Find out the answer »

If air is heated and its starts to go towards the space, what is the reason for this? Do you think the air molecules will get accelerated and because of this they will resist Earth’s gravitational force?

Find out the answer »

My 9 year old wants to know if a single atom exists in a certain state of matter — or must it be associated with other atoms in order to define a state?

Find out the answer »

With the latest telescopes, we can look at some galaxy's some 13 billion light years away, correct?

And that is much older than the earth is thought to be. I also heard that we have seen what the universe looked like only a short time from its birth. So how can all this be true? If nothing can travel faster than light and the light from that moment in time would have passed the spot the earths current location long ago, how can we see that light? What am I missing? I can not fathom how we beat the light from the early universe to this spot. Something doesn't add up for me, so can someone break it down for me?

Find out the answer »

I've read that orbiting objects like the space station stay in orbit because they are falling at the same rate the Earth is curving away underneath them.

What I don’t understand is their downward velocity should be increasing because it is caused by gravity / acceleration due to gravity. Shouldn’t it be “falling” with a greater velocity the longer it travels? Does it reach a terminal velocity like that of a skydiver? If so Why?

Find out the answer »

Under acceleration, a helium-filled balloon inside of a car will jump forward in the direction of acceleration. I have been searching for the reason why with no definitive results. This is the dilemma: An acquaintance of mine, who has a degree from Johns Hopkins is attempting to argue for some magical force that drives the balloon forward, also that it has something to do with gravity.

Find out the answer »

Hello, I am trying to figure out the practice behind the experiment I've heard about in a National Geographic documentary, so please help me a bit.

How do they generate entangled particles in the lab (photons)? Also, how do they make photons to interact with each other and what kind of interaction do they make?

Find out the answer »

I’m not a physics guy, but with all the discussion around the disaster in Oklahoma recently it had me pondering a terminal velocity question. From what I understand, any object with mass would possess a terminal velocity.

Since air has mass, what would be the terminal velocity of air? Specifically, how fast can a tornado/hurricane/natural disaster hurl air before it reaches a terminal velocity?

Find out the answer »

How does one measure the kinetic energy of the ejected electrons resulting from the photoelectric effect?

My understanding is that the KE of the ejected electrons was dependent on the frequency of the incident light, not the intensity. A higher intensity light, however, would [have] ejected MORE electrons; provided that the light's frequency is high enough to overcome the work function of the metal.

Thus, it seems to me that an ammeter would show a higher current either way. A higher frequency light would produce faster electrons and a higher intensity light would produce more electrons. Given that current is a rate of charge (I = dq/dt), how did Einstein know that the frequency was the primary factor for the KE and not the intensity?

Find out the answer »

My 7 year old son Ben (who is sitting next to me now) has recently become interested in how small things can be. He is not convinced that nothing can be measurably smaller than a Planck length because whatever is Planck sized can always be divided into something smaller.

He thinks perhaps Planck lengths can be divided into energy beams that then become infinite.

Find out the answer »

A friend of mine claims to notice that when he takes a hot frying pan (with a warm, insulating handle), and pours cold water into it, the handle seems to get hotter. He thinks it is because the handle is less insulating than the air, thus the path of least resistance is through the handle.

This would make sense to me when you take the pan off of the heat, but he claims that it isn't until the water hits it that the handle gets significantly hotter. If this is true, what does the water have to do with it? If anything, wouldn't the water become the path of least resistance, and heat would move from the metal to the water, and from the handle to the air?

Find out the answer »

My 4 year old would like to know: "If marbles are made of glass then why don't they break when you throw them?
Find out the answer »

In figure skating, if you are doing a spin on ice and you leave your arms spread out it creates resistance. If you pull the arms in toward the body, you create less resistance so you spin more easily. How do I express this with mathematical equations in physics?

Find out the answer »

Does Einstein's relativity of simultaneity mean that two events cannot be simultaneous or that we cannot prove that two events occurred simultaneously?

Find out the answer »

If somehow there was a tunnel straight through the center of the earth and we dropped a capsule through it, what will happen to the capsule? Would the tunnel shoot the capsule into space?

Find out the answer »

Assume two photons are moving in opposite directions from each other from a common light source. How fast would they be traveling relative to each other? Twice the speed of light? If the speed of light is the ultimate speed limit in the universe, how can something travel twice that speed?

Find out the answer »

I have a question about waves and particles. Since waves and particles seem to be somewhat interchangeable at the subatomic level, at what wavelength does the wave / particle duality stop?

Find out the answer »

As the nucleus gains mass by adding protons and neutrons does the size of the nucleus increase into the empty space of the atom or does the innermost orbital move away from the nucleus? Basically, is an atom of Ununoctium larger than an atom of Sodium?
Find out the answer »

In the proton-proton chain reactions which happen, for instance, in our Sun, two protons collide and form a proton and a neutron. However, this just blows my mind.

What is the mechanism by which a proton simply loses its charge, becomes slightly more massive, and turns into a neutron?

Find out the answer »

Prof. Brian Cox recently stated that the universe is 100 billion light years in diameter. Since the universe is no more than 14 billion years old and nothing exceeds the speed of light, shouldn't it be about 28 billion light years in diameter, not 100?
Find out the answer »

If photons have no mass, why is it impossible for them to reach the escape velocity of a black hole? It seems that a massless particle/wave would have no difficulty escaping the gravity of a black hole, no matter how massive the singularity.
Find out the answer »

Can electricity (static or not) be used to move very large objects? Could you somehow control a sufficiently strong electrical current through the air or across a surface to lift a log or a car? Are there certain objects it could lift and certain ones it couldn't?

Find out the answer »

I am lost about neutrinos. I thought a neutrino was just a neutrino since it is neutral. What are the differences between electron, muon, and tau neutrinos?
Find out the answer »

How can 'greenhouse' gases transfer heat to the earth's surface? Doesn't that mean energy is being transferred from something low energy to something at a higher energy? Does this theory violate thermodynamics law?
Find out the answer »

How was the universe created if physics states matter can neither be created nor destroyed?
Find out the answer »

Since water molecules are negatively charged on one side and positive on the other, can you freeze a container of water which you place in a magnetic field and create an ice-magnet?
Find out the answer »

A ninth grader wants to know what it's like to be a physicist. Here is one physicist's response.

Find out the answer »

On Saturday, I accidentally left a full cup of diet soda sitting in my car. It was originally full of ice, which of course melted over the course of a day and a half. When I got into my car on Monday morning, the straw was just over half full of soda, extending about 2" above the full level of soda in the cup. This condition held constant for quite some time, even when the cup was lifted and jiggled/disturbed. Once I had taken a tiny sip, the level of soda in the straw went back down to where I would have expected to find it (at the same level as the soda in the cup). Given that this was a standard lid (with an opening at the top for the straw that is certainly not airtight, nor was the top opening of the straw airtight at all) I could not imagine how the soda in the straw was being pushed or pressured to a higher level than the soda in the cup. The weather over the weekend was cold, but not freezing, averaging in the low 50's. Why did the liquid level in the straw from my soda rise above the liquid in the cup after being left in my car for the weekend?
Find out the answer »

Why do planets rotate counter clockwise around the sun?

Find out the answer »

What is an electric dipole?
Find out the answer »

Why does a flame from a fire or match go up?

Find out the answer »

If the recent result of the tests of the speed of the neutrino are validated by other research groups what are its implications for the standard model of particle physics as it has been described to date?

Find out the answer »

There seems to be a lot of debate about how accurately CERN measured the departure of their neutrinos. Could they not aim them at some other neutrino detector in the world and just use the difference in distance and time from the readings in Italy as this would eliminate the error in not knowing exactly when the neutrinos left CERN?

Find out the answer »

When carrying out the double slit experiment using electrons or buckyball molecules, do the particles have to be traveling at near light speed velocities to produce an interference pattern?

Find out the answer »

When we talk about an object on an incline, the force of gravity has two components, one vertical and one parallel to the incline, as you know, while the normal force is matched in magnitude by the vertical component of gravity. When we talk about a banked road, however, the normal force becomes the force whose both components are considered, while gravity becomes the force that is matched by the vertical component of normal force. In a way, they almost reverse their roles. Why is that?

Find out the answer »

Do laws of physics pose limitations to biological evolution?
Find out the answer »

If you shake the sun, how long would it take before it had an effect on the position of the earth?

Find out the answer »

Since the earthquake in Japan the country has been having trouble with their nuclear energy plants and possible meltdown. The question is why aren’t they using lead to absorb the radiation?

Find out the answer »

Does an ice cube have heat energy (kinetic energy)? If so, does a glass of water with ice have more heat energy than a glass of water without ice?

Find out the answer »

If a helicopter hovers in a fixed position for 24 hours will the earth rotate around it?

Find out the answer »

Are airport whole body x-ray scanners safe for frequent travelers?

Find out the answer »

I built a sand art box for performing sand art but I have a problem. The sand I use keeps bouncing around on the glass as opposed to being pencil thin. How or what kind of sand can I use to remedy that?

Find out the answer »

If an object is sitting on the ground, not moving, is it accelerating towards the earth? I ask because gravity is an acceleration and gravity is always acting on all objects, but acceleration measures the change in speed of an object. So if it is not speeding up, but gravity is acting on it, is it accelerating?
Find out the answer »

Can you explain why a penny under a glass beaker of water disappears? If you add some water to top of the penny and return it to under the beaker it is visible.

Find out the answer »

How when pressure is decreased, volume increases?

Find out the answer »

How can you make electric currents from magnets?

Find out the answer »

Why do ice cubes sometimes stick to your skin?

Find out the answer »

Why does a cyclist bend or lean during a turn?

Find out the answer »

What are the scientific reasons for spin or curve on a soccer ball? What forces are affecting this?

Find out the answer »

Why is it said that increasing heights of building affect the revolution time of earth?

Find out the answer »

Why does a stationary body above the surface of the earth not change its position after some time while the earth is moving? Suppose if we place an object above the surface of the earth, would it be at the same position after some time and why?
Find out the answer »

Is it true that pressure exerted by a human foot is more than than exerted by that of an elephant?
Find out the answer »

Explain how beautiful sunrises and sunsets are the result of dust in the atmosphere?
Find out the answer »

How is the photoelectric effect used to produce a current in a photovoltaic cell?
Find out the answer »

Can you change 50 degrees and 85 degrees each into Radians?
Find out the answer »

Question: I want to ask why water is shaped like a ball when it is in space without gravity?
Find out the answer »

What does physics have to do with weight lifting?
Find out the answer »

If someone was 137 and 5 foot 7 in. how many newtons would it take them to escape the gravity of earth?
Find out the answer »

I understand now why the sky is blue, but why are sunsets red and orange? - AB, Oak Ridge, TN
Find out the answer »

Is it possible to have an instantaneous zero speed but still have an acceleration? Please give an example. - J
Find out the answer »

Would a vertical pipe 50 miles long, one end at or near sea level and the other end in space, suck air into space? It seems as though the vacuum of space should create a flow through the pipe since the pressure at each end is different. - P
Find out the answer »

It was my understanding that the velocity of an object falling through air has to do with gravity and wind resistance only. Does the object's velocity have anything to do with its weight or mass? - JVN, Brisbane, Australia
Find out the answer »

How does a siphon work? — C
Find out the answer »

What happens when you use the tab on an inside rearview mirror to diminish the brightness of the headlights behind you? RC, Vail Colorado
Find out the answer »

How does pressure affect humans? Why do our ears pop at high altitudes? — KC, Chino Hills, CA
Find out the answer »

How do the machines that concentrate oxygen out of the air work? These machines are used by people with breathing problems - DK, New Orleans, LA
Find out the answer »

On earth, two objects of different masses fall at the same rate. However, in space, larger masses exert greater gravitational attraction than smaller masses. This seems inconsistent. What am I confusing? - DD, Miami, FL
Find out the answer »

Why does aluminum foil spark in the microwave? - BB, Iowa City, IA
Find out the answer »

How does MP3 recording compress digital music by factors near 10? I roughly understand zip encoding, but that usually only reduces file sizes by 2 or less. — J, Greenbelt, MD
Find out the answer »

What is mass? I thought mass was the same as weight, but my friend pointed out that in orbit you have no weight but you still have mass. So what actually IS mass? — TP, London, UK
Find out the answer »

Why is it that when you hear an airplane it sounds like it is coming from somewhere behind where the airplane really is? Is it because light travels faster than sound? - S, TX
Find out the answer »

Some lights in my home are controlled by two different switches. How is this possible? - V
Find out the answer »

Why is it that when you severely kink an Ethernet cable, you can no longer transmit data on it? That cable contains 4 twisted pairs of copper wires and kinking the cable doesn't break or short out those wires. Why should the kink matter? - DB, Evansville, Indiana
Find out the answer »

My brother asked me if there's a difference in weight between an empty and a full hard disk. He was kidding, but it made me wonder if there might be a small difference on the molecular scale. Is there? — RVO, The Hague, The Netherlands
Find out the answer »

How does house insulation work? — JB
Find out the answer »

What are the advantages and disadvantages of convection ovens over standard ovens? – KK, Rochester, NY
Find out the answer »

My electric toothbrush charges up by sitting in its base unit. There is no metal-to-metal contact—only plastic-to-plastic. Since the plastic is non-conductive, how does it charge? – RS
Find out the answer »

How does the placement of a car's center of gravity affect it? - SM, York Beach, Maine
Find out the answer »

Why are the earth and other large celestial objects always spherical? – SP, Mumbai, India
Find out the answer »

How does a catalytic converter work? - WK
Find out the answer »

I've heard that digital encoding on audio CDs represents a pressure wave. But audio has so many components like volume, pitch, and timbre; how can the binary encoding of a pressure wave encompass all these attributes? RY, Madison Wisconsin.
Find out the answer »

Why does a steel ball bounced on a steel surface bounce higher than any other ball on the same surface? - JL, California
Find out the answer »

Why if you drop a ball from say 2 meters does it bounce higher than a ball dropped from 1 meter? - E
Find out the answer »

How do water-bottle rocket work? I know about Newton's third law and everything, but I don't know how it all goes together in a bottle rocket. - Z, Vancouver, WA
Find out the answer »

Why is the sky blue? CL, Hong Kong
Find out the answer »

Do bubbles last longer in cold weather or hot weather? Why? — A, Alpharetta, Georgia
Find out the answer »

After a tropic thunderstorm, why does it feel so nice to breath? - WM, Kota Baru, Kelantan, Malaysia
Find out the answer »

For a science project, I made a parallel circuit and a series circuit. Each is powered by a 6.3-volt battery and has three six-volt lights on it. Why is the series circuit so much dimmer than the parallel circuit? - ML, Woodbridge, CT
Find out the answer »

I have a question about a tennis racquet: when I hold the racquet like a frying pan (plane of the head horizontal) and give it one flip, it changes from smooth up to rough up (or vice versa). When I flip it with the plane of the head vertical, nothing peculiar happens. In both cases, I try not to impart any rotation about the long axis. - GF, Shawnee, Kansas
Find out the answer »

I can't understand the instruction stated on my tennis racquet about the relation between string tension and string power. It says "higher tension for more control and less power and vice versa". How can it happen? – AT, Hong Kong
Find out the answer »

What does physics have to do with global warming? — ML, New York
Find out the answer »

Why does an electric generator slow down when you begin to use the power it is generating? – WV, Waverley, South Africa
Find out the answer »

If you coupled a motor to a generator and connected them to the same power source, would the generator be able to recycle wasted power from the motor and thereby reduce costs? — JH, Australia
Find out the answer »

Why can a human being sense some accelerations, such as in a car or airplane, but not others, such as free fall? - MDJ, Ozark, MO
Find out the answer »

In his book "Understanding Physics," Isaac Asimov writes "As the earth rotates about its axis, the surface of the earth is continually undergoing an acceleration inward toward the center of the earth (just as the moon does in revolving around the earth." Does that mean that the acceleration on the surface (g = 9.8 m/s2) is directly related to the centripetal acceleration of an object traveling in a circle (a = v2/r)? - DW, Raleigh, NC
Find out the answer »

How do I explain the difference between the following two situations to my junior high son: (1) The horizontal velocity of a bullet fired horizontally from a gun has no effect on how long the bullet takes to hit the earth, i.e., how long it takes gravity to bring the bullet down to earth. (2) The horizontal velocity of the Space Shuttle orbiting the earth does affect how long it takes for the Space Shuttle to hit the earth. The velocity of the Space Shuttle makes it keep missing the earth in its free fall. – MMH, Ohio
Find out the answer »

Why do we see only one side of the moon and the other side is permanently hidden? - KS, Vienna, Austria
Find out the answer »

Why does humidity affect temperature? - H, Heyworth, IL
Find out the answer »

How does temperature affect the sound of a flute? — S
Find out the answer »

Why does my older farmhouse feel warmer and seemingly easier to heat the colder it gets outside? I live 20 minutes north of Maine, which should give you an idea what kind of winter temperatures we have to endure. - JS, Greenfield, New Brunswick, Canada
Find out the answer »

Do you think humans will ever be able to predict the weather? BL, Schenectady, New York
Find out the answer »

I'm studying how wind power is used to produce electricity and would like to know how a generator works. - MO, Canandaigua, New York
Find out the answer »

As a downhill cyclist, I enjoy riding "drop-offs," i.e. riding off the edge of drops in the ground and landing at the bottom. It seems common sense to me that the faster I go when I hit the edge, the easier the landing. However, some of the physics I have learned in school suggests that my horizontal velocity would not matter, as my vertical velocity would be the same in any case. Is there something I am forgetting? - IE, Oban, Argyll, Scotland
Find out the answer »

An electron beam, such as the one found in a TV picture tube, is composed of negatively charged electrons. Why is it that this beam does not rapidly spread out owing to the electric repulsion? I realize that the tube has various focusing magnets and such, but I would think the electronic repulsion would be a serious problem. - JT, Buffalo Grove, IL
Find out the answer »

Why does a basketball bounce higher when it has more air in it? - SR, Charlotte, North Carolina
Find out the answer »

Why do mylar balloons lose or seem to lose helium when taken outside in the cold and blow back up or seem to blow back up when you take them back in where it is warm? — TS, Alabama
Find out the answer »

How do astronauts weigh themselves while they are in space? - LE
Find out the answer »

How can we see anything? - D
Find out the answer »

If a truck full of parrots hits a bump in the road and all the parrots begin flying around inside the truck, does the truck's weight stay the same or not? HJ, Thisted, Denmark
Find out the answer »

We're confused about the difference between fluorescent and halogen bulbs. Fluorescent bulbs are classified as hazardous waste because they contain mercury. Do halogen bulbs also contain mercury? - LR and APM, Washington, DC
Find out the answer »

What causes the smoke produced when you extinguish a candle flame?— SB, Plymouth, England
Find out the answer »

Why is it easy to stay on a bike while moving, but impossible once it stops? - AS, Switzerland
Find out the answer »

Which color is hotter, red or violet? — LL, Falls Church, Virginia
Find out the answer »

If you fell into a swimming pool full of Jello, would you be able to swim to the other side? — LM, Charlottesville, VA
Find out the answer »