What is Shadow: Definition and 122 Discussions

A shadow is a dark (real image) area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or a reverse projection of the object blocking the light.

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  1. M

    A Related Rates Shadow Problem

    EDIT: I think I figured it out - sorry for taking up space. I posted my answer below.* Homework Statement A light is at the top of a 16-ft pole. A boy 5 ft tall walks away from the pole at a rate of 4 ft/sec. a) At what rate is the tip of his shadow moving when he is 18 ft from the pole...
  2. B

    What causes the shadow below a whirlpool in a pool?

    Hi there, I have noticed that when the wadding pool I work at is draining, a small whirlpool appears over the drain in the center of the pool. When the sun is shining a shadow appears at the bottom of the pool(2.5-3 feet deep) below the whirlpool. The shadow is larger than the whirlpool...
  3. D

    Creating shadow of an object by radio waves

    Hi guys, We all know that a shadow could be generated by radiating light waves to an object. Would it be possible to design a system with radio waves, an object made by a special material and a sensor plane in order to create a shadow of the object on the plane? Cheers!
  4. M

    Shadow of light (Cardone et al)

    Subject: http://arxiv.org/abs/physics/0504166" DOI: http://dx.doi.org/10.1142/S0217979206033085" I am more interested in the apparent empirical results than any particular characterization the authors suggest, which are laid out clearly enough simply by comparing figure 5 to table 3...
  5. G

    Change in rate of a man's shadow length

    Homework Statement A man 1.8m tall walks at 1.5m/s along the edge of a road which is 8m wide. A street light 6.3m high is situated on the other side of the road. How fast is the length of the man's shadow changing when he is 8m past the point on the road opposite the light? Homework...
  6. A

    Shadow Matter,Psi-phenomena and Survival

    I've recently read(partially) the book written by G.D.Wasserman "Shadow Matter and Psi-phenomena and possible Survival of Human Personality". Here is description from Amazon: "A scientist casts new light on psychic phenomena, such as clairvoyance, telepathy, and 'out of body experiences'. He...
  7. M

    Basic Related Rates: Rate of change of length of shadow

    Homework Statement A 6-ft man walks away from a 15-ft lamppost at a speed of 3 ft/s. Find the rate at which his shadow is increasing in length. Homework Equations Pythagorean Theorem, Theorem of Similar Triangles (ratios of corresponding sides are equal) The Attempt at a Solution...
  8. D

    Shadow of vertical circle on wall?

    A ball is spun in a vertical circle on a string. A light is shining from the side of the circle so that a shadow of the balls motion is shown on a wall behind it. The shadow is simply a circle moving up and down in a straight line (I can't attach the image). The amplitude of the shadow is 0.5m...
  9. H

    Similar Triangles, Light and Shadow.

    Homework Statement A man 6 feet tall walks at a rate of 5 feet per second away from a light that is attached to a pole 15 feet above the ground. At what rate is the length of his shadow changing when he is 30 feet from the base of the pole? I get that this is really like a two similar...
  10. N

    Cast Focused Shadow: Solutions and Tips

    Hi, I have an object and I need to cast its shadow on a surface. The object is about 20cm away from the surface. When I point a light into it, if the light is too close (30cm), it casts an unfocused shadow. When I move the light away from the object, the shadow gets more and more focused. At...
  11. C

    Trigonometry homework: length of shadow

    Homework Statement The sun was shining in the yard of engineer Jack Smith. Jack was reading in the shadow cast by the pine tree planted by his grandfather Tom Smith. The length of the horizontal part of the shadow was 6.0 m and the height of the vertical part of the shadow on the wall was 3.6...
  12. P

    Why Does a Nearby Light Source Produce a Blurry Shadow?

    I was wondering why does a large, nearby light source produces a somewhat blurry shadow? While looking for a reply i found that when we are close to own own shadow, the outline of your shadow is sharp because the Sun is so far away. But i couldn't quite understand it.
  13. S

    Why Can't We See Mountains on the Moon from Certain Places on Earth?

    I may be wrong, and I will feel pretty stupid if i am, but i think that we can see Earth's shadown on the moon, that's why it has cycles right? if so, then why can't we see mountains and stuff from certain places on the earth. Is it because the moon is so far away?
  14. D

    Shadow Dynamics with Varying Velocity

    Homework Statement A small light source is located a distance L from a vertical wall. An object of height h moves with constant velocity v towards the wall, causing a shadow on the wall. At time t = 0 the object is located at the source S. (a) Compute the height of the shadow, D, as a...
  15. O

    Problem involving ratios to find the length of a shadow

    Homework Statement The shadow cast by a vertical pillar in Alexandria at noon during the summer solstice is found to be 1/8 the height of the pillar. The distance between Alexandria and Syene is 1/8 the Earth's radius. Is there a geometric connection between these two 1-to-8 ratios? I already...
  16. stevmg

    Stargazing Velocity of shadow of solar eclipse

    If a solar eclipse is visible near the equatorial region on the Earth, does it move from West to East at about 1000 miles/hr?
  17. T

    How Does Karagiozis Confirm Einstein's Theories in a Shadow Play?

    A new story of the Greek traditional shadow theater with muppets. In this story except of Karagiozis (the main character of the greek shadow theater) there are also characters like Einstein and Newton. Karagiozis help Newton to make his theory but at the end, (8:00+) happens a total solar...
  18. A

    Why Do Shadows Bend When Objects Come Close Together?

    good morning/evening/afternoon everyone. i always wanted to know why does shadow bends? if you hold any 2 objects togather and from distance, slowly bring them togather but never touch, at some poing the shadows start getting mixed up.. for instance if you point your index fingers and bring...
  19. S

    Related rates question, shadow

    Homework Statement A man 6m tall walks away from a light 10m above the ground. If his shadow lengthens at a rate of 2m/s, how fast is he walking? Homework Equations The Attempt at a Solution I have nothing.
  20. E

    Speed of Shadow: A Mysterious Phenomenon

    My friend was explaining to me once how the only faster then light is shadow. It was very odd. He said that if we have a star being orbited by a planet with a period of one days and surronding this system is a "wall", upon which to cast a shadow, 1 light year away. So, if the planet circles the...
  21. B

    Comparing Half Earths: Horizontal or Vertical Shadow Line?

    Sorry, I'm a newbie here and didn't know how to start a new thread, so I posted a question in another forum and then figured out how. I'm trying to redirect answers here. I'm arguing with a friend about how a half-Earth would appear from the Moon. Since we see the Moon in phases, it makes...
  22. S

    Webpage title: How Fast Does the Shadow of a Dropped Ball Move Along the Ground?

    Homework Statement a basket ball is dropped from a height of 10 m and at a horizontal distance of 2 m from a light pole. A light source at the top of the light pole is 15 m above the ground. How fast is the shadow of the ball moving along the ground one second after the ball is dropped? it can...
  23. R

    Is it possible to restructured an upright object from its shadow only,

    is it possible to restructured an upright object from its shadow only, for example an cube or any model?
  24. S

    Related Rates: Shadow Problem with Moving Object

    Homework Statement A spotlight on theground shines on a wall 12 m away. If a man 2m tall walks from the spotlight toward the building at a speed of 1.6m/s. how fast is the length of his shadow on the building decreasing when he is 4m from the building? The Attempt at a Solution x=4m...
  25. U

    Find Shadow Length Decrease Rate for Spotlight 12m Away

    Homework Statement A spotlight on the ground shines on a wall 12 m away. If a man 2m tall walks from the spotlight toward the building at a speed of 1.6m/s, how fast is the length of his shadow on the building decreasing when he is 4m from the building? Homework Equations x2 + y2 = z2 The...
  26. C

    Related rates falling rock with shadow

    Homework Statement a light shines from the op of a pole 50ft high a ball is dropped from the same height from a point 30 feet away from the light , how fast is the shadow of the ball moving along the ground .5second later. So is the ball falling at 32ft/s^2 would we set it up...
  27. C

    Brightness of ISS in Earth's shadow

    I observed the ISS when it was almost overhead and well inside Earth's shadow with binoculars. The brightness was perhaps magnitude 8 or so, I'm not sure. I observed the ISS enter the Earth's shadow when it was at 60 degrees over the horizon, the brightness declined rapidly as it entered the...
  28. S

    Shadow Rate of Change: Solving a Geometry Problem

    Homework Statement A street light is on top of a 20-foot pole. A person who is 5 feet tall walks away from the pole at the rate of 5 feet per second. At what rate is the tip of the person's shadow moving away from the pole when he is 20 feet from the pole? 2. The attempt at a solution...
  29. D

    Shadow Height on Wall: 2.6m Light Source

    1. A rectangular piece of cardboard 21.7cm high is held 1.0m in front of a point source of light. The cardboard is 2.6m away from a wall. How tall is the shadow on the wall? I have no idea how to do this my prof never talked about this in class and I looked threw the book with no help. I...
  30. M

    Caustic curve - shadow in the cup

    Hello, I need help... I have been assigned in physics to look at the shadow in the cup and mysearch shows me caustic curves... I have very little information on this to do a 4 page report on... can someone please point me to some sites, url etc on this... many thanks
  31. U

    Finding rate of change of shadow problem.

    Question: A 1.85 m tall man is walking toward a 12 m tall street light at night at a rate of 2.2 m/s. How fast is the length of his shadow changing when he is 12 m from the street light? so, using similar triangles, i got that (x+y)/12 = x/1.85. I can rearrange this into x= or y=, but then I...
  32. TheFerruccio

    Need an algorithm for satellite passing through non-penumbral earth shadow

    I have a simulation with a satellite that orbits Earth in 3d. Earth's shadow, for simplification purposes (the satellite is pretty close to earth) is either on or off. There's no light diffraction here. It can be represented as a cylinder with radius ~6378km, and an axis which aligns with...
  33. M

    Crazy Elliptical shadow problem

    Homework Statement The figure shows a lamp located three units to the right of the y-axis and a show created by the elliptical region x2+4y2\leq5. If the point (-5,0) is on the edge of the shadow, how far above the x-axis is the lamp located? Homework Equations Implicit Differentiation...
  34. L

    Does Fire Cast a Shadow?

    Hi. So my friend thinks he's smart, and one time, while we were talking, he asked me whether fire can produce shadow. Of course he does not know the answer, but knowing him, he asked me this question to show that I am not smarter than him. Nevertheless, his question started bothering me, because...
  35. H

    Exploring Pendulum's Shadow on C: V vs PHz

    Let's experiment with: A = a very distant source of light B = pendulum at a given distance from the light source C = a huge white wall Let's suppose the pendulum vibrates at PHz. Let's suppose the white wall is moving in the line of the light source and the pendulum at the very...
  36. rocomath

    Related Rates street light shadow

    A man standing 3 feet from the base of a lamppost casts a shadow 4 feet long. If the man is 6 feet tall and walks away from the lamppost at a speed of 400 feet per minute, at what rate will his shadow lengthen? How fast is the tip of his shadow moving? I'm unsure of how to solve the 2nd part, a...
  37. A

    Casting a Large, Sharp Shadow Through Lace

    I am an artist. I am trying to cast a large sharp (in focus) shadow through a piece of lace onto a wall. It either turns out large and blurry if it is far from the wall, or sharp and small if it is closer to the wall. I have tried the following experiments: 1. Increased the focus and...
  38. Z

    Exploring the Shadow & Light of Water Striders

    What accounts for the large shadows cast by the ends of the thin legs of the water strider? What accounts for the ring of bright light around the shadows? Here is my picture (below) (ATTACHED)
  39. J

    Fresnel diffraction; geometrical shadow

    What is geometrical shadow qualitatively? please don't refer me to hyper physics
  40. M

    Confirm Correctness of Ant's Shadow Movement Equation

    Homework Statement (Q) A lamp is placed at the point (5,0) and it casts the shadow of an ant onto the y axis. When the ant is at point (1,2), how fast is the ant's shadow moving when the ant's x-coordinate is increasing at the rate of 1/2 units/sec and its y-coordinate is decreasing at...
  41. A

    Finding the Rate of Change of Shadow: A Man 6 ft Tall

    Homework Statement A man 6 feet tall walks at a rate of 5 feet per second away from a light that is 15 feet above the ground. When he is 10 feet from the base of the light, (A) at what rate is the tip of his shadow moving? (B) at what rate is the length of his shadow changing?Homework...
  42. M

    Related Rates: Calculating the Speed of a Moving Shadow

    Question A street light is mounted at the top of a 15 foot tall pole. A man 6 ft tall walks away from the pole with a speed of 6 ft/s along a straight path. How fast is the tip of his shadow moving when he is 40 ft from the pole? Attempt Well actually, I've drawn it out and stuff, but I was...
  43. B

    Finding Velocity of Top of Object's Shadow

    Homework Statement A small source of light S is located at a distance L from a vertical wall. An opaque object with a height of h moves toward the wall with constant velocity v_vec of magnitude v. At time t= 0 , the object is located at the source S. Find an expression for v_s, the...
  44. N

    Calculating Hawk's Shadow Speed

    3. When the Sun is directly overhead, a hawk dives toward the ground with a constant velocity of 5.00 m/s at 60.0 degrees below the horizontal. Calculate the speed of her shadow on the level ground. I am having some trouble picturing this problem in terms of a coordinate grid (this is in a...
  45. EnumaElish

    NYT article about the speed of shadow > c

    The thought experiment is to glue a "bat" figure on a light source (e.g., lamp). The shadow created by the bat figure is projected into the void, as in Batman. The trick is to rotate the lamp. As the lamp rotates, so does the bat shadow, projected into the space. The trajectory of the shadow...
  46. ZapperZ

    VOTE Photo Contest - Me and My Shadow

    This promises to be another round of difficult voting. Please vote for the picture that best represents our theme: shadows! 1. hypnagogue http://img231.imageshack.us/img231/9183/archbt9.jpg 2. Task 3. larkspur 4. Janus...
  47. ZapperZ

    PF PHOTO CONTEST - Me and My Shadow (6/16-6/22)

    Me and My Shadow This week, your pictures must clearly show shadows of objects and/or persons. The picture may or may not include the object itself, but the shadow must be there.Contest Rules: 1. Any digital photo or digitally-scanned photo relevant to the theme will be accepted within the...
  48. B

    Sun Sensor Performance in Earth's Shadow

    Hi, Will a sun sensor work if the satellite is in the Earth's shadow? thanks!
  49. heusdens

    Big Bang afterglow fails intergalactic shadow test

    News article on Science daily. If the cosmic microwave background radiation was a remnant of the big bang fireball, galaxies should cast shadow on this CMBR. But this test seems to fail, as only 1 out of 4 galaxie clusters cast shadows...
  50. G

    A Man and His Shadow: Velocity and Relationship with Sunlight

    Homework Statement One man, with height h, is inside a room. On the ceiling of the room there is a candle that is at a height H from the floor. The man moves in a straight line with velocity v1, passing below the candle. a) Determine the velocity of the shadow of his head projected on the...
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