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. Two candles making shadows of one another on opposite walls

I copy and paste the problem as it appears in the text along with the diagram alongside. It is clear from the image that the base of the shadows don't move - only their tops would move either up or down. Let us assume the time ##t_1>t_2##, implying that candle 1 burns at a slower rate. How would...
2. MHB Shadow Lengths: Friend vs Tree

At certain time of day, the shadow of your friend who is 5 ft tall measures 8 ft. At the same time, the shadow of a tree measures 28 ft. Draw a diagram to represent the situation. How tall is the tree?
3. B Can a Planet Have a Moon that Never Casts a Shadow?

I am a newbie, and really uninformed (read stupid.) Here is my question: Would it be possible for the Earth (or any planet,) to have a moon whose orbit was such that it never came between the sun and the Earth? In other words, could we have a moon that never cast a shadow on the Earth? Or is...
4. How will light react in this situation....

Dear Physics Forum, I need help with this problem. In the diagrams above I try to show my difficulty. My main problem is working out how shadow will fall on a completely flat surface with the light source at more or less a 0 or 180 degree angle (depending on how you want to look at it) ...
5. A Oddly specific question for help regarding a satellite in a shadow

Hello fellow Space People, Currently trying to create a function in MATLAB to input an R and V vector and have it spit out all the orbital elements as well as shadow entry/exit locations. I have the Vallado "Fundamentals of Astrodynamics" book and I've used it religiously. I searched on here...
6. MHB 2.6.284 AP calculus Exam Lamp and Shadow related rates

yes I know this is a very common problem but likewise many ways to solve it ok I really have a hard time with these took me 2 hours to do this looked at some examples but some had 3 variables and 10 steps confusing to get the ratios set up... ok my take on it is here see if you can solve...
7. How accurate can the shadow of a large sundial be?

Saw a sundial the other day and it occurred to me that a larger one would be more accurate. But then shadows get less sharp at a distance so there is a trade-off. What would be the maximum accuracy that can be achieved by making a sundial larger?
8. I The Shadow Of An Atom - False Colour Images Reveal Structure

I've been adding some renderings I did of the M87 black hole on a different thread and was asked to elaborate on the source of this technique which was investigating images of the shadow of an atom. You can look up the original experiment on Google, as well as observe the final image. The...
9. Why does flowing water cast a shadow?

I found that water flowing from a tap is casting a shadow, somewhat like this: If you see through the water flowing from the tap, you can see that the pink colour of the wash basin is visible almost clearly. What is the cause of the flowing water casting a shadow? Is it because the...
10. Decreasing size of person's shadow as they walk toward a lamp

Homework Statement If a man of height 6ft moves with 5ft/sec velocity towards a lamp hanging at 15ft height, then at what rate his shadow will decrease? Homework Equations Not sure but dynamic equations can help. The Attempt at a Solution I have no idea about how I can approach.So I want some...
11. B Is our 3D universe a shadow of a 4D Universe?

Is it possible that our 3D universe is just a shadow in 3D space of 4D or higher dimensional reality? And we are limited in our perception of it by our 3-dimensionality. In other words like Flatlanders would just see s square of a cube sitting on the plane or passing through the plane...
12. Calculate Height of Light Pole from Shadow Length

Homework Statement At the outside, there is a vertical stick with a length of 1.1 meter and its shadow on the surface of an Earth is 1.3 meter, there also is light pole and its shadow length is 5.2 meters, what is the height of that light pole? Homework Equations Trigonometry equations to...
13. B Explaining the Lack of a Visible Edge in Shadows of Clouds over the Sea

I have seen shadows of clouds over the sea. What could be the explanation? Let me explain why there needs to be an explanation: Radius of sun: ~600000km Distance to sun: ~150000000km (assumed) distance to cloud: 2km This means that there should be a 16 metre edge around the shadow where the...
14. MHB 2214.17 Related Lamppost And Shadow

ok just seeing if this is ok where does the 35 come in ? I tried to follow an example but?? is not x=35
15. Question: Shadow Speed Related Rates

Homework Statement 2. Homework Equations Similar triangles The Attempt at a Solution $$\frac{y}{30}=\frac{50}{x}~\rightarrow~x=\frac{1500}{y}$$ $$\frac{dx}{dt}=-\frac{1500}{y^2}$$ $$s=16t^2=16\frac{1}{4}=4$$ $$\frac{dx}{dt}=-\frac{1500}{16}$$ The answer should be ##~\displaystyle...
16. Using Gamma Ray reflector to reduce mass of Shadow shield

Let's say we have manned space vessel powered by a highly power but radioactive rocket engine, producing a lot of deadly gamma rays. The classical answer to this problem is to use a shadow shield. However, Nuclear Shadow Shields are very heavy. What about the idea of instead of trying to absort...
17. Completely black shadow cast through perfectly clear water.

Today while filling a mortar tub with water for all the wildlife in my backyard and surrounding area, I noticed that vortex swirls produced a completely black circle shadow, surrounded by a white sunlight ring, the ring was very bright and the reflection on the bottom of the tub (black) was very...
18. Physics Connecting with Medical Physicists: Tips for Shadowing and Networking

Hi, I've recently graduated with a BS degree in applied physics and I'm interested in pursing medical physics. I'm currently looking for medical physicists to shadow and I haven't been able to find any. I know that hospitals that have radiology oncology departments are likely to employ...
19. MHB Computing height given shadow length and angle of elevation

Simple geometry can compute the height of an object from the object's shadow length and shadow angle using the formula: tan(angleElevation) = treeHeight / shadowLength. Given the shadow length and angle of elevation, compute the tree height. #include <iostream> #include <cmath> using namespace...
20. Why shadows become dark when light intensity increases?

I observed following phenomena today: in my room with some lightings, there is a stuff toy placed in front of a wall. The ambient lighting doesn't cause any shadow on the wall currently. Now, I switched ON a torch and pointed it to a stuff toy which was kept in front of a wall and a shadow...
21. How Does Teller Cut a Flower by Manipulating Its Shadow?

This magic trick was performed by Teller on Penn and Teller: Fool us. In this trick the magician is basically cutting a flower by doing movements on a shadow. I don't see here sleight of hand or any threads attached. The screen may be recorded but how the real flower or artificial is being cut...
22. Project sharp shadows from LED

Using a high-power LED light (the surface mount kind, about 4x4mm with 120 degree viewing angle) I'd like to project shadows of a fine metal mesh onto a wall. I have tried various lens arrangements and found that placing a pinhole in front of the LED makes the sharpest shadows. This makes...
23. Question about higher dimensions and what connects them

It's my understanding that, if we ignore the temporal dimension and just focus on spatial ones, then you get to the third dimension by starting with a point and adding perpendicular lines to them. Once you've done this a couple of times, you get three dimensions. Obviously, to the layman, it...
24. How a very short λ enable light, not obliterate all shadow? (diffraction)

Hello all, Guys, I just pointed out that I actually lacking in somewhere in the understanding of the phenomenon of diffraction of light, of which I am aware from no less than 10 years. Recently I revised Huygens wave theory of Light and studied in what ways Newton criticize it. At one of the...
25. Earth Shadow Tapering: Why Does It Happen?

The Earth casts a shadow. Why does this shadow taper?
26. Calculate Length of Shadow from Two Street Lamps

Homework Statement Hi everybody; a teacher of mine has given me a photo of two street lampd and their shadows; he has said to me that it's height is 3 metters, and the distance between the lamps is metters, and with that information I should be able to tell the length of the shadow. The image...
27. What is faster the cannon ball or its shadow?

I'm trying to finish my physics homework and one of the questions is somewhat philosophical. Problem: A cannon ball is shot at noon (12pm), what is faster? The cannon ball or its shadow? That's all the question is :p
28. Lagrange Multipliers and Shadow Prices

This is a homework in mathematical modeling and optimization; we're up to Lagrange multipliers and shadow prices. 1. Homework Statement A manufacturer of PCs currently sells 10,000 units per month of a basic model. The cost of manufacture is 700$/unit, and the wholesale price is$950. The cost...
29. Shadow of Steam: Seeing the Unseen

My mother was ironing clothes a few days ago, and the iron was really hot. It was giving out steam, i couldn't see it, but i could see its shadow on the wall. How so?
30. Calculate shadow path & size + object size based on distance

What are the variables I need to take in account if I want to calculate shadow path and size? I will try to simplify my questions. I have a 2d circle (radius: 28) which means the size of the circle (in box) is 56x56 at specific point (lets say 300,300). I tell the 2d circle to go in specific...
31. Maximize Sunlight: 3 Object Shadow Formation

How should I place three objects for e.g three pencils so that no shadow is formed for them throughout the day(light source:sunlight to be considered)??
32. (Elastic collision / shadow problem) I suspect my professor is wrong.

Homework Statement Suppose that two elastic balls moving through three dimensional space collide and rebound, conserving both kinetic energy and momentum. The balls cast shadows, and these shadows moving over a flat two-dimensional surface come together, collide and rebound. Now pretend the...
33. Earth's shadow in the atmosphere

If a clear view is available of the horizon,theory says that I'll be able to view the Earth's shadow(the curvature of the Earth in the direction of sunlight). Is it possible to calculate the curvature of the Earth just by looking at this different colored band in the horizon? Was it done...
34. MHB Solving the Tightrope Walker's Shadow Problem

Im stuck on this question! so can someone please please help me? Thank you! A tightrope is 40 ft above ground between two buildings that are 60 feet apart. A tightrope walker starts along the rope and walks from building A to building B at a rate of 2 feet per second. 80 feet above the starting...
35. Can a Gamma Ray Burst create a shadow on Earth from the Sun?

Would a nearby Gamma Ray Burst (GRB) cause the Sun to cast a shadow on Earth if it were to shine from behind it?
36. Find the velocity of the shadow variation

Helo, I've been working out this exercise, but my solution and the text's aren't the same. Homework Statement We have a spotlight on the floor located at a distance of 30.5 m from a wall of a building. There is a person 1.83 m tall between the spotlight and the wall moving away from the...
37. Earth's axial tilt and the shadow from the Sun

I have watched the Sun's shadow make its trek from the solstice moments for many years. I have it marked and like to observe it as Earth's tilt reaches it's maximum point, from Summer to Winter and back. I used a heliodon to built a large structure (80 feet long/12 feet tall=roofline of my...
38. Solve x3-6x2+1=0: Find Real Numbers & Reasons

Homework Statement Determine how many real numbers satisfy the equation x3-6x2+1=0. Give reasons for your answer naming any theorems you use. 2. The attempt at a solution let:f(x)=x3-6x2+1 →f'(x)=3x2-12x for stationary points:f'(x)=0 →3x(x-4)=0 ∴x=0 or x=4 to determine...
39. Shadow on Wall: Light Blur from Wave or Quantum?

Hello, As we know, if one turn a light blub(and no other light is present) on and put his hand in front of a wall to make a shadow, the shadow is blurry, depending on the distance between the hand and the wall. I want to ask you if this blur is caused by quantum uncertenty (like this...
40. Why does the shadow of Skylab appear so large in this video?

Please ignore the UFO reference and watch for 5 seconds in the below link. One can see the shadow of Skylab on the Earth. Skylab is in a 235 mile orbit above the surface of the Earth. Clouds are about 5 miles above the surface of the Earth. So the camera capturing the images is at least 230...
41. Speed of moving shadow due to light source

Homework Statement A girl 5 feet tall is running at the rate of 12 feet/second and passes under a street light 20 feet above the ground. Find how rapidly the length of her shadow is increasing when she is 20 feet past the base of the street light. The Attempt at a Solution I let the distance...
42. MHB Rate of how fast a shadow grows as you walk

So here I thought it might be something to formulate a triangle, or actually two: So the problem is asking me to find the derivative of the shadow's length with respect to time: \frac{dB}{dt} I think the triangles are similar: \frac{15}{A+B} = \frac{6}{B} \\ \\ \cdots \\ B = \frac{2}{3}A...
43. A man standing x ft. from a light pole, length of man's shadow?

Homework Statement A man 6ft. tall is standing x ft. from a light pole 15 ft. high. Express the length of the man's shadow L as a function of x. Homework Equations Pre-Calc. NO TRIG The Attempt at a Solution I assumed that the man's shadow creates another like triangle within in the larger...
44. Shadowing a Physicist: Is it Practical?

I know for most jobs it is recommended that you shadow someone of the profession you are interested in and I was wondering if this is possible with a physicist. Is it possible to shadow a physicist for a day in their workplace to see a first hand view of what they do in day to day life? (note: I...
45. Angle between line and its shadow on a plane

Homework Statement A line intersects a vertical wall at 40.78° (that is, 49.22° with respect to the normal vector of the wall). The line is contained within a vertical plane perpendicular to the wall such that the aforementioned angle is measured with respect to the plumb line dropped from the...
46. Determining the Radius of the Moon (Ratio and shadow measurements)

Hello. I have been going through some old OU books on the sciences and started working through an excercise when I came to a stumbling block. I have come here in the hope that someone may be able to shed some light on my problem. This is all for personal study as I am not enrolled on any...
47. Calculate Speed of Hawk's Shadow on Ground

When the Sun is directly overhead, a hawk dives toward the ground with a constant velocity of 4.15 m/s at 54.5° below the horizontal. Calculate the speed of her shadow on the level ground.Homework Statement Homework Equations vxi=vicosθ vyi=visinθ (i think) The Attempt at a Solution...
48. Finding the Height of an Object Casting a Shadow that is Moving at a Given Speed

I'm trying to solve a seemingly basic question but it seems to be taking me towards some advanced dynamics that is over my head. Any help would be appreciated. (If it matters, this is not a homework problem - I am simply curious about the answer and how to solve it.) Homework Statement...
49. Why you can't prove a single mathematical thing beyond a shadow of a doubt

Oyez! I'm an amateur philosopher and I'd like to start up an interesting debate. The topic will be mathematics (and, in general, everything) and how it is not logically possible to prove such a system. This is my informal argument: 1. Humans live in a "reality" governed by laws, axioms...
50. What is the origin of the strange shadow in a laser beam?

Hello! I have for you some questions about the lasers. When ordinary laser beam directed at a small ball (few millimeters) on the screen I saw a bright spot in the middle of the shadow. What it is due?