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# Physics/Correct terminology

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QUESTION: Hello. I am not in school. Even when I was, physics was a challenge. Ok, I was wondering the difference between velocity and speed, or are they interchangeable.

For instance. Say there is a boat, and one boat raced up to that boat and attach a wire to it and share that 'rate' they are going.

Would the correct word be they shared the same 'velocity' or 'speed'? Or use the term Kinetic energy? Thank you.

ANSWER: It's a specific distinction in this case.  Velocity has a direction in x, y, and z coordinates as well as a magnitude.  Speed is the magnitude.  Rate=speed="how fast."  Velocity = "how fast and in (x,y,z) direction."

---------- FOLLOW-UP ----------

QUESTION: Oh!

If you wanted to absorb that magnitude, would it be 'kinetic' energy you would capture?

ANSWER: Kinetic energy depends on the square of speed or velocity and depends on the mass...they're not the same type of quantity at all.

---------- FOLLOW-UP ----------

QUESTION: Ok, maybe I"m asking wrong. Suppose, one could 'steal' Superman's ability to travel very fast. What is that 'fast'? Magnitude? Does it have to have a direction as well? Thank you.

Answer
That question doesn't really make sense.  Stealing Superman's ability to travel very fast isn't the same as stealing is current speed or velocity.  But if you were to steal his speed, it would necessarily have to have a direction, so you'd be stealing a velocity.  Even if you bounced off him at some random angle, you'd acquire a velocity (because motion has to have a direction), and the "size" of that velocity would be your speed.

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#### Dr. Stephen O. Nelson

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I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

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I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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