Not a member yet?    Get Free Membership    Username:        Password:         Remember me        Forgot your login?   Ask the Experts   University Departments   Discussion Forums   Online Chat   Einstein eGreetings   Science eStore Become a Sponsor      Ask the Experts: Classical Mechanics What are Kepler's laws of motion and what exactly do they mean? Why the law of momentum conservation is not violated when a ball rolls down a hill and gains momentum? What do external forces have to do with equilibrium? How many times should all the people in the Northern-Hemisphere should jump simultaneously into the air to alter the Earth's orbit by 1 m? When a car is driving up a hill, is the friction between the tires and the ground static friction or kinetic friction? What are the six simple machines used in the study of physics? If a car is traveling with a helium-filled balloon in the back seat, and the car suddenly stops, what happens to the balloon? What is the physics involved in skydiving? How can one prove that the world is round? What are Eigen Values? I have often read that scientists are searching for the next prime number. My question is why? What use is it? How can knowing the next highest prime number be of any benefit? Is it possible to place a satellite in geostationary orbit over the north pole? What exactly is the purpose of the spoiler on a car and how does it work? If I am on a merry-go-round with a friend, and the friend is closer to center than I am, are they going faster then I am? What is it aliasing? When it occurs? Why does your hand look funny when you move it fast in front of the tv or computer screen? How is force related to momentum? What would be the force required to accelerate 1 gram to 20% of the speed of light? What is the physics involved in snowboarding? How does a sailboat move upwind? Why does a golf ball slice or draw? What is the difference in the flight of a golf ball hit with back-spin and one hit with top-spin? Does the sun move at all? I have a clear plastic ball with some electronics inside. When bounced, LEDs flash on and off. I suspect that it contains a piezoelectric crystal and I would love to know how it operates. If I am standing on a mountain, Am I going faster than someone at sea level? If so, is my day shorter or will the higher vantage point of the horizon allow my day to seem longer? How does a cat land on its legs when dropped? How do sea navigators measure their ships speed? What are the advantages of ABS braking systems compared to other hydraulic braking systems? Do sub-atomic particles obey Newtons Laws of motion? Is it purely coincidental that the moon rotates on its axis in synch with its revolution around the Earth, keeping the same face always pointed toward us? Where in the United States is the force of gravity the strongest? Does seismic activity on Mauna Kea effect the operation of the telescopes there? Do the moon and sun appear larger on the horizon, or is it just me? Can energy be converted back into mass? Why does the stream of water from a faucet become narrower as it falls? Can you hit a golfball into orbit on the moon? How is time a function of the fabric of nature, and not perception only? Where do I find a list of metals with their heat expansion index? What are the physics involved in throwing a frisbee? And why its specific shape? What is the difference between the inertial and gravitational mass? Do gyroscopic forces from the wheels make any significant contribution to the rideability of a bicycle? Which of these 3 sports will be the hardest or the easiest to play on the moon? Basketball, Soccer or Football? How fast would the Earth have to rotate so that it would neutralize gravity? Are coriolis forces strong enough to cause an open basin of water to create whirlpools moving in opposite directions when the basin is transported 20 feet either side of the equator? I saw this demonstrated in Kenya (for money), but I wonder if there wasn't a trick. What happens when a tablecloth is pulled out from underneath a table setting, and everything on the table stays put? What is the angular velocity of the Earth around the Sun? How do we get it? If there is anti-matter, couldn't there be anti-energy? How does a dunking ducky work? What is the difference between a physical change and a chemical change? If nothing sticks to Teflon, how does it stick to the pan? How can I prove that the earth rotates around the sun? If both friction and air resistance were eliminated from acting on the swinging pendulum, would gravity act on the pendulum to slow it down and eventually stop? Lets just say a huge asteroid hits the earth at the right speed and with the right amount of force and stops it's orbit around the sun. How long would it take for the earth to plummet into the sun? If I know the diameter of a balloon can I find it's volume? If space is a vacuum, then how do space capsule's retrorockets steer? Do you get wetter if you run or walk in the rain? Is our moon's gravitational field strong enough to retain a gaseous envelope and is there a gas with a sufficiently high molecular weight that could be used to create an 'atmosphere' for our moon? A stationary van is filled with 1 tone of bees sitting down. Is it true that the overall weight of the van is the same if bees are flying instead of sitting? Assuming the probability of obtaining heads in coin flip is exactly fifty percent, why should a test group of a ten flips produce less accurate results than one of one million flips? If you hover any distance above the earth (in a helicopter, for example) for a day or so, why aren't you and the helicopter occupants on the other side of the world if the Earth is going through its normal revolution? Could a circular space station simulate the Earth's gravity by spinning at a certain velocity? (I have seen something like this in A.C. Clarke's 2001) I am curious as to what causes the Earth's spin, and why does the Moon not spin? As an engineer, I know that friction does not depend upon surface area. As a car nut, I know that wider tires have better traction. How do you explain this contradiction? I am 11 yrs old and soon to be going to Magic Mountain to ride a roller coaster for the first time. My Dad says that I really don't need a safety harness when the roller coaster goes upside-down because centrifugal force will hold me in. Is this true? Which is heavier, wet or dry sand? The tires of airplanes (at least the big ones) are inflated by nitrogen (instead of air). Why is this done? I'm an actor playing the role of a balloonist and I want to be able to explain in scientific terms why helium and hydrogen make balloons rise. Atmospheric pressure is supposed to be very large. Then why is it that we, along with everything else on the earth, do not get crushed under this tremendous pressure? Why is it that when you put your finger over the tip of a hose the water shoots out farther? Does a car use the same amount of gas traveling a given distance at 60 mph than it does traveling the same distance at 10 mph (or any other speed)? And if so, does a person burn the same amount of calories walking a given distance as running it? Is there any device that has, for a moment or so, zero momentum and possess kinetic energy? How can you measure the mass of the Earth or any other planet? Is the rotation of the earth considered the initial kinetic energy for a rocket before take-off? What is rest mass? How to explain it especially to the high school students? What is escape velocity? Is it easier for an airplane to travel East to West or West to East? In rotational motion, when the radius is decreased, does velocity increase or decrease? I often get confused between the terms centrifugal force and centripetal force could you please enlighten me? Who is responsible for the theory/maxim/idea ... 'every action has an equal but opposite action'? A pendulum is hanging in a lift and is oscillating. The lift is given a free fall. What will happen to the bob of the pendulum? Why doesn't friction depend on surface area? Where can I get a list of friction coefficients for different materials? Why is simple harmonic motion 'simple'? Is there a complex harmonic motion? If you were in a plane and shot a bullet vertically down from a gun and dropped a bullet by hand, at the same time, would they reach the earth at the same time? Does a car makes more pressure to the floor when it goes faster, or the car could fly if it goes even faster? I was told by my Physics instructor that there is such a thing as negative time. Is that true, or was he just pulling my leg? If Newton's law of motion, which states that any object in motion will remain in motion, is true, then why is it that as a comet gets close to the sun and it melts, and a tail forms, and why wouldn't it be just a big ball of melted stuff? Two cars traveling at 60 mph collide head on. Another car crashes into a wall at 60 mph. Which one has more damage? If the term 'absolute motion' has no meaning, then why do we say that the earth moves around the sun and not vice versa? How come a drop of water can stay hanging from the ceiling without falling immediately on the floor? How does it stick to the ceiling surface? Are the electrons spinning around the nucleus of an atom travelling faster than the speed of sound? Why does a piece of chalk produce a squeal if you hold it incorrectly. What determines the pitch you hear? Do we weigh more at Death Valley than on top of Mount Everest and if we do would it be from gravity or from atmospheric pressure? Why does oil float to the top in liquid if you try to mix it with the liquid? Is the velocity of a baseball pitcher's arm 100 MPH if his pitch is clocked going that fast? Can an object be said to: accelerate from 50 km/h to 0 km/h? Or must one say that the object has decelerated? Is it true that in the late 1800's they took away or added 11 days to the calendar that didn't exist? Why is it, that if you lower your hand flat into, say, a pool there is no or hardly any resistance but if you were to raise your hand and slap it down hard into the water, there is so much resistance? How they can reach zero gravity in a plane (when astronauts are practicing)? Since the sun is one giant ball of gas, what force holds its consistent shape and size? Why doesn't it expand and burn up quickly? Is the angle at which the object rebounds, in a perfectly elastic collision, from the surface equal to that at which it is incident? When you throw an object into the air, is the initial velocity the same as the velocity just before it hits the ground? If so, why? Why does a solar eclipse move from west to east, while the sun moves from east to west? Why is it that when one is taking a hot shower, the shower curtain tends to be pulled inward, inside the shower(as opposed to being pushed outward)? What is terminal velocity? How can I more easily visualize what a horse-power means? Where is the force of gravity stronger, on the top of Mt. Everest or at sea level? Is weight determined strictly by the distance between and mass of two objects, or are other factors figured in; i.e. can a person be considered weightless underwater? How fast must a car be travelling to generate 1G (gravity) of force on itself and it's occupants when stopped, as if hitting a wall? Would this be perpetual motion: 1) You make hydrogen from water using energy. 2) you let the H2 rise through a pipe capturing all its energy. 3) you burn the H2 in a fuel cell at its highest height. 4) Then you let the water from the fuel cell run down a pipe capturing all of its energy. 5) Now all the energy you captured from the H2 rising, the fuel cell burning,and the water falling is used to make more H2. What speed defines Mach 1? and why? If I fire a cannon straight up into the air, the cannon ball slows down as it rises to its apex, then speeds up as it falls. At any given distance from the ground, is the ball travelling at the same speed on the way DOWN as it was on the way UP? When was the first experiment done, or how old is experimental physics? What is a geo-stationary orbit? Are there any other orbits? If I were in an elevator that was free falling, would it help at all if I perfectly timed a jump before it hit the ground floor? Would anything help the situation? What is a sonic boom and how is it produced? If there was a hole through the earth would you be stopped in the middle due to gravity or would you fall straight through? Why can you ride a bike with no hands? How a satellite can pick up more speed after circling the sun? I believe it is called the slingshot effect? Wouldn't any speed gained from the gravitational pull of the sun be counteracted by the same gravity when the satellite was distancing itself from the sun? Why do dimples on a golf ball allow it to travel farther? Why your ears pop when you are riding on an airplane? What is the physics behind the voice change which occurs when one inhales Helium? How do you determine the distance of lightening from where you are standing using the sight of lightening and the sound of the thunder? Is the geographic NORTH pole of the earth a magnetic NORTH pole? Once you have reached the north pole of the earth, what happens to your compass? Which way would it be pointing? What are Newton's three laws? How do airplanes fly and where can I find more information about it on the internet? In movies why do wheels of a moving car appear to rotate backwards to the actual direction? How do yo-yos work? Why do they come back up after being thrown down? What is the physics behind a frisbee in flight? Can you compress a liquid (water)? I know that gravity keeps us on the earth, but what prevents us from being pushed or pulled through the floor, earth, etc. (besides concrete, wood, and soil)? Does it have something to do with opposite forces? Why can a person lay on a bed of nails and not be injured? What is this scientific theory called? Do falling objects drop at the same rate (for instance a pen and a bowling ball dropped from the same height) or do they drop at different rates?

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