James
  • Member for 6 years, 5 months
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  • Avon Lake, Ohio, USA
A bob hanging in an accelerating train moves backward. What is the force moving it backward?
38 votes

The answer by rghome is correct when Earth's surface is chosen as the reference frame. Now consider this with the train car as the reference frame. According to the Equivalence Principle, the effect ...

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Backyard experiments to falsify the Flat Earth theory
33 votes

I live close to Lake Erie and often see scenes like in this picture. Note that the bottom of the cargo ship cannot be seen due to the curvature of the Earth.

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Is it more work to put more (apparent) effort to get the same outcome?
9 votes

The dog does more work when pulling harder. Work is force times distance. Consider the following two walks. Walk 100 meters while pulling with 10 Newtons of force. Walk 100 meters while pulling ...

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Backyard experiments to falsify the Flat Earth theory
6 votes

Can you convince your friend that time zones are for real? If he will believe that it is nighttime in China when it is daytime in the US, then his disk theory can't be correct.

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Is it in principle possible to store energy more efficiently (per kg) than as antimatter?
5 votes

I'm not a physicist, but I will attempt to answer. Mostly, I will restate a lot of your question and attempt to show why antimatter is the most efficient. As you know, a 1 kg mix of matter and ...

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if light source is bigger than the object, it is possible that shadow of the object is bigger than the object?
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5 votes

In this case, the likely explanation is that the surface of the water near the "floater" is not flat due to surface tension. This causes the light rays entering the water near the particle to be bent,...

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Why stress always flows through the shorter/stiffer path?
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4 votes

The majority of the load tends to be carried by a stiffer member. Stress is load per area, so if the stiffer member has a larger cross-sectional area then the stress is not necessarily higher. As to ...

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How to intentionally make water evaporate at faster rate at room temperature?
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4 votes

In addition to the other good answers... Agitate the water so that it's surface area increases. For example, stir the water or blow air (bubbles) through the water.

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How would this system behave?
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3 votes

In the absence of friction and drag, your 3D contraption would move forever given some initial velocity in the same way that a thrown ball would move forever if not acted on by external forces. You ...

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What is the mechanism of the semi-transparent glass?
3 votes

I don't think such a thing exists. Rather, the lighting on the two sides of the glass determine which side may be seen through. If your eye is on the bright side, then you see the reflected light ...

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G-force: difference between gravity and acceleration of an object
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2 votes

In the top image, your body want to accelerate downward relative to the ground. The ground prevents your acceleration through the force on your feet which you feel. In the bottom image, your body ...

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What does an acceleration greater than $g$ feel like?
2 votes

If you were being accelerated downward at 2g via a rope tied around your legs, you would feel the same as if you were hanging upside down with no acceleration. When in free fall, you would accelerate ...

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Is it possible to suggest a physical experiment in which measurement errors are dramatically increasing? (due to the accumulation of errors)
2 votes

A very simple example might be as follows... Measure the period of a single swing of a pendulum. Predict the position of the pendulum an hour from now.

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Where does the tritium on the Earth come from?
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2 votes

Wikipedia says that the half-life of tritium is 12.32 years, but that naturally produced tritium on Earth is the result of cosmic rays interacting with atmospheric gases. Tritium occurs ...

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How to prove that Gravity happens in one plane?
2 votes

I had never heard of Noether's theorem and I still don't understand it, but here's an intuitive explanation... Imagine that the initial velocity vectors of the two bodies lie in the same plane. The ...

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Drop of water sliding on a surface (curve of *steepest descent* )
2 votes

The following argument assumes the droplet is a point particle as mentioned by @m3tro in his comment. I think your question also assumed a point particle because you ask about "...THE curve of ...

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Analyzing dynamics of an object in a frictionless hemisphere
2 votes

My Assumptions: Gravity is acting toward the left in your diagram. The bead begins the experiment motionless at the lowest point in the hemisphere. Question: Will the bead climb up the frictionless ...

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Stiffness of a Cantilever Beam
1 votes

As others have said, the simple beam deflection equation assumes small deflections. You say that... Logically it should provide more resistance as deflection goes on increasing It's true that you ...

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Rolling a cylinder using a rope having one end fixed and another end mobile
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1 votes

The force in the rope (tension) $F_R$ is half the attractive force on the cylinder $F_C$. $$F_R=F_C/2$$ But the upper left end of the rope is moving twice as far as the cylinder. $$X_R=2X_C$$ So the ...

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Will splitting a tensed string by the ends and in the middle make the two long parts not go flying around?
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1 votes

The centers of mass of those two big parts would not move, assuming that the cutting could be done without imparting a force to the string. Conservation of momentum means that the center of mass will ...

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Will a dropped ball compress faster than it decompresses?
1 votes

I agree with the answer from @ManuelFortin In addition, the reason for the slower decompression is elastic hysteresis. As explained in the article, materials don't quite obey Hooke's Law, which ...

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To lift an object, do we need a force equal to its weight, or greater than its weight?
1 votes

Maybe you've heard of Isaac Newton's second law of motion... $F=ma$ where $F=$ net force on an object $m=$ mass of object $a=$ acceleration of object In your question, you ask about a situation ...

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Time taken by a Magnifying Glass to heat Metal
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1 votes

In your comment, you say you are trying to heat the following object... a soda can tightly selaed and painted black at the bottom ... inside the can is water. using a 70mm magnifying glass. In ...

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What is the work done by a force acting on a deformable body?
1 votes

If the forces were constant as the deformations increase from zero to the fully deformed state, then the work done at each force would be $$W=F\delta$$ However, the text is making the assumption ...

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Why is there a constant pressure when lifting a weight with expanding gas?
1 votes

The comment from @SwapnilDas was a good hint for you. For a slow process (quasi-static), the force pushing down on the piston is constant, equal to the weight of the piston and block. The opposing ...

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Hydrostatic force on spillway gate?
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1 votes

Imagine that the water height is at a point where the force at B is exactly zero but the gate has not yet moved upward. Part of the weight of the gate will now be supported by the hydrostatic force, ...

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Loading condition for analysis
1 votes

Approach 1 is correct. Consider a free body diagram of Link 2. The forces on Link 2 must balance. A force F will therefore exist acting on Link 2 toward the right. There will be an equal and ...

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Ideal rolling with friction - torque perspective
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1 votes

Your false assumption is that there is a non-zero static friction force at the point of contact. If an ideal ball is rolling at a constant velocity on an ideal level surface with no rolling ...

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Moving contained liquids vertically
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1 votes

The vertical movement would cause no extra forces in the container, but the acceleration at the top and bottom would cause some very small compression waves in the water. Think of an elevator. You ...

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Spring behaviour under high atmospheric pressure
1 votes

Damping The density of atmospheric air is approximately 1.225 kg/m$^3$. At 3000 atm, the density would be 3675 kg/m$^3$ compared to the density of water of 1000 kg/m$^3$. I don't know the viscosity ...

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