Relative motion Definition and 283 Threads

We can determine the earth’s movement in relation to other astronomical objects, but we have no idea of our absolute movement, correct? The earth is spinning and revolving around the sun which is revolving around a galaxy that is expanding from other galaxies in the universe. The entire...

My attemp : ##\vec r_1## : Position of the river in reference frame. ##\vec r_2## : Position of the walker in reference frame. ##\vec r_x## : Position of the walker measured by the river. We have: $$\vec r_1 + \vec r_x = \vec r_2$$ $$\vec v = \dfrac {d \vec r}{dt} $$ $$\vec v_1 + \vec v_x =...

Hello everyone, I've been thinking about 2nd postulate of relativity, it seems that and the Michaelson-Morley experiment seems to imply that there is no ether, but I was thinking about a special situation that doesn't seem to go against that postulate. I think my question is basic so hopefully...

TL;DR Summary: What should be the geometries of two contacting solids that may have a relative rotation and translation along the same axis? a) Consider two rigid bodies that have a relative motion characterized by a rotation and a translation with respect to the same axis (like a bolt and a...

We only measure time via the relative movement of a standard, agreed reference, a clock for example. If we replaced all instances of "time" in the formulation of SR and GR by "relative motion [ie, of an agreed reference]", would SR/GR remain correct/consistent? Or does SR/GR rely on a deeper...

(Please refer the image below. ) The velocity of Nick ##v_N=\omega r## and the velocity of John ##v_S=\omega R## is depicted. The relative velocity of Nick with respect to John will be ##v_{NJ} = \omega (R-r)##. The velocity is along the tangent to the circle centred at B. If Nick were to move...

This is much like the "grain of sand" at near speed of light hiting Earth, but now targeting Jupiter with a needle! What if... Any way, which is the correct way to analyze this kind of scenarios? For example, I think than being the speed of the needle near c, is nonsense to think about the...

I think the question is wrong. My answer : But it should be wrong because : I think the question is wrong … But I'm not sure …

vcanoe_wrt_ground = 3 m/s + (-6) m/s = 3 m/s - 6 m/s = -3 m/s Thus, if I understand this correctly, the rower will never reach his goal 36 m away as his canoe's resultant velocity is negative (i.e., his canoe is effectively going downstream even though it is trying to go upstream). My only...

Given the relativity concept between twin 1 and twin 2 what is the difference between relative motion and 'relative' acceleration? Are not either twin experiencing the differential between them as a consequence of acceleration. When twin 1 instigates motion relative to twin 2, a moving carriage...

Does the position of the origin for the body’s rotating coordinate frame 1) stay fixed to the moving body or 2) does it stay fixed to the inertial frame, yet still able to rotate as the body rotates with the only restriction that it cannot translate with the body i.e. only affixed at the...

I do not agree, this is bullocks. We can simply set up position vector of ##\vec A(t)## and ##\vec B(t)## with respect to the fixed center of the carousel, their relative velocity is simply ##\frac{d (A-B)}{dt}## or ##\frac{d (B-A)}{dt}## Since this is a pretty popular book, I am wondering if I...

I'm having trouble understanding the plane one This is what I understand so far v I'm sitting at a chair right now and if I compare my relative motion to the ground my relative velocity would be 0m/s but if I compare my motion to the solar system I would be moving very fast. I just can't grasp...

Hi, I'm stucked in this exercise. I don't know how to proceed. Any hints I appreciate it.Two bars of the same proper length L, moves in the same way on the x axis. In the referential of one of the bars the time interval between the events, when the extremity right of one bar and the extremity...

Hi, I am just writing a post to follow up on a previous thread I made which I don't think was very clear. The question is mainly about how to use the below equations when there is also a rotation of the body around the fixed reference point. Please see the diagram here to see how the vectors...

its a short question...

Velocity of B wrt C = (v +v*cos 60) i^ - vsin60 j^ = (3v/2)i^-((3)^(1/2)/2v)j^ But since C is also moving this initial velocity would vary. So how to find a function which defines its path and hence I can find time at which the particles meet. I was told to take rotating frame of reference that...

In Introduction to special relativity by Resnick,there is a thought experiment to compare lengths perpendicular to relative motion as given in the below image. What if we try to perform such an experiment to compare lengths parallel to relative motion? Suppose there are two horizontal rods...

I know that ##v_{M/S}=v_M - v_S##. I also know that ##v_M = (-24.1;0)##. Then, using some trigonometry, ##v_S=(-19.3 sin 30°;19.3 cos 30°)##. So I can find ##v_{M/S}##. But that doesn't tell me anything about the angle ##\beta##.

The thing is that my professor said that if the velocity of ##A## is ##400 cm/s##, the velocity of ##B## is ##200 cm/s## because "##B## is connected to two parts of the rope and ##A## is conected just to one part", and he also said that that ##200 cm/s## is the velocity of ##B## with respect to...

Here, I have two doubts 1) if the surfaces are frictionless, then there's no force being applied on the ##x' axis## of ##m_1## except from the weight, so it should be sliding, shouldn't it? So, there's no force that I could apply to ##m_2## to keep ##m_1## in equilibrium since any force that I...

Well, ##r(t)## in ##A## is just a vector ##(0;y)## because is tangent to the trajectory. Then, from the perspective of ##B## the particle moves in an uniform circular motion. Is this right? The velocity from ##B## must be ##\omega##, right? And what about acceleration?

Well, first I tried to understand the relation between the velocities and accelerations of both bodies and I got that the velocity of ##B## is half the velocity of ##A##. This is because a change in length of the cord "that touches ##A##" must be equal to the change in length of the two cords...

Well, I tried plugging the data in the formula. I know that ##\vec a_b = 0; \vec \omega=3 rad/s ; \vec r## can be calculated using trigonometry. Then I also know that ##v_{relx}= 10 cm/s##, ##a_{relx}=15 cm/s^2##, ##\vec {\dot{\omega}}=-10 rad/s^2##. But how do I get ##v_{rely}## and...

As the problem asks for the spaceship's perspective, I know that I should take ##\vec v_S=0## and ##\vec v_M=24.1-19.3## because the motion is relative to the spaceship. Then, the relative velocity of Mars and ##SM## should have the same direction. If they have the same direction, that angle...

The first doubt that comes to my mind is "I have to determine the acceleration with respect to what?", because the problem doesn't tell. Then, I have some problems when having to plug the data in the formula of acceleration. ##\vec a_B=0## because the origin isn't accelerated, ##\vec{\dot...

I think my approach is quite wrong, still I gave it a shot: First I know that ##v_A=13.3 m/s=r\omega=60\omega \rightarrow \omega=0.2 \frac{rad}{s}## Then $$\vec a_A=-r\omega^2 e_r=-2.4 e_r$$ But ##e_r=\cos{\theta}i+\sin{\theta}j## and substituing the latter in the acceleration equation I have...

Consider the example of flashing light in spaceship. The observer in the spaceshipe and the observer in the Earth measure different times. Both observers could argue that the clock of the other tick slower(motion is relative). But is anyone right ? I mean the one will measure proper time...

This problem seems pretty simple but I don't understand how the correct answer is 500,000 smaller than what I calculated. You have an electric field that has a magnitude of 10^6 V/m in the positive z direction. I assumed (though it was not stated) that the cause of this field was a sheet of...

Here's a experiment. There is a magnetic field vertically downward and a charged particle is kept inside it. Simple. Does it experience a force? Now if we move a speed of 2m/s relative to the frame of rest charged particle. Then it must experience a force right?(Becuz now its velocity is not...

Homework Statement 15.1 The airspeed of the plane is 200m/s, directed north. If the wind speed is 30m/s in the direction shown, determine the ground speed and the course (angle θ) of the plane. Homework Equations The Attempt at a Solution Is it so far correct the above? More questions...

Homework Statement A river of width 4 km flows at 5 km/h. A swimmer whose speed relative to water is 4 km/h, starts swimming from a point A on a bank. What minimum distance will the swimmer have to walk on the other bank to reach point B directly opposite to A? [/B]Homework Equations Vba = Vb...

Hi everyone! Sorry for the bad english! Quick question Just to see if I understood: If a person on a spaceship moving at 0.7c in relation to a person in the earth, and both of then agreed they started making microwave popcorn at the same time (like when the spaceship is just above the head of...

https://www.physicsforums.com/attachments/221718 Say if we have two particles P, and Q, traveling at velocities Vp and Vq respectively. If it is IMPOSSIBLE for Q to collide with P, let us find the distance of closest approach. So from the frame of reference of P, itself is stationary, and Q is...

Homework Statement If a river is going 6 km/hr relative to the ground, a boat is going 14 km/hr relative to the river, and a man is jumping from one end of the boat to the other at 6 km/hr relative to the river. What is the speed of the man relative to the ground? I'm stuck between the...

Homework Statement A plane is taking off from an airport directly west of the airport it wishes to touch down in. The plane in still air can travel with a constant speed of 730 km/h. If a wind is blowing constantly at 92 km/h [45° S of E], at what angle must the plane fly to compensate for the...

If two objects are traveling on paths at 90 deg to each other such that they will converge at a point how do we describe that motion. For example 2 cars are approaching a 4 way intersection and will collide. They see each other as moving diagonally yet when they collide one will t-bone the...

Is there any way to synchronize two clocks already in relative inertial motion? If so, how? And I am not sure exactly what “synchronize” would mean in that context. Maybe it would mean that their readings, or at least their running rates, would match when their relative motion was stopped? There...

Homework Statement In the figure below, a radar station detects an airplane approaching directly from the east. At first observation, the range to the plane is d1 = 412 m at 40° above the horizon. The airplane is tracked for another 123° in the vertical east–west plane, the range at final...

Consider an electric charge Q with rest frame R and a closed conductive loop L with rest frame R'. Q is moving relative to L, and vice versa. In R, the loop is moving and receives no magnetic flux from Q thus no voltage according the integral form of Faraday's law. In R', the loop receives...

Homework Statement Two observers having identical instruments carry out identical experiments to study the motion of a massive particle. First observer concludes that the particle is moving in a straight line with constant velocity while the second observer concludes that the particle is moving...

Hi, I'm reading a book explaining relativity. I previously understood the subject in layman's terms but am now confused. The author has introduced relative motion in an invariant universe with the concept that motion through space is only relative to the observer. Given this, I'm now...

Homework Statement A small airplane wants to fly from A to B which is 200 km due south. The wind is blowing towards the east at a velocity of 50 km/h. If the airplane can move through the air at 300 km/h, find the direction the plane should be heading; the speed of the airplane relative to the...

Based on my current understanding of the problem I do not see this following derivation as valid, although this is what was given in my course notes. Although this particular example is from an undergraduate physics course this is not a homework problem: I'm confused about the underlying...

Homework Statement A farmer is throwing bales of hay off the back of his tractor with a speed of 3 m/s relative to the tractor, which is moving west with a speed of 7 m/s. Determine the speed and direction of hay bales relative to the ground. Homework Equations subtract the speeds, since they...

Homework Statement Homework Statement A newspaper boy throws papers sideways onto the porches of his customers while riding his bicycle along the sidewalk. The sidewalk is 15m in front of the porches. The boy throws the papers at a horizontal speed of 6m/s relative to himself, and rides the...

Homework Statement After flying for 15 min in a wind blowing 42 km/h at an angle of 31° south of east, an airplane pilot is over a town that is 50 km due north of the starting point. What is the speed of the airplane relative to the air? Homework Equations Vx of wind=42km/hr*cos(31) Vy of...

Homework Statement Homework Equations a= omega^2*r The Attempt at a Solution a_A/B = a_A - a_B a_A = 10^2*r (-î) a_B = 10^2*r (+ĵ) a_A/B = 10^2*r (-î) - 10^2*r (+ĵ) => -200 î -200 ĵ why is the answer 200 î -200 ĵ (accelerate in +î direction) ?

Homework Statement Homework Equations v_theta = r * theta_dot 1 knot = 1852 m The Attempt at a Solution v_0 = 6 * (1852m/h) * (1/3600 h/s) = 3.087 m/s