Block Definition and 998 Threads

A block of the periodic table is a set of elements unified by the orbitals their valence electrons or vacancies lie in. The term appears to have been first used by Charles Janet. Each block is named after its characteristic orbital: s-block, p-block, d-block, and f-block.
The block names (s, p, d, and f) are derived from the spectroscopic notation for the value of an electron's azimuthal quantum number: sharp (0), principal (1), diffuse (2), or fundamental (3). Succeeding notations proceed in alphabetical order, as g, h, etc.

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  1. V

    Friction problem of a block sandwiched between 2 surfaces

    I don't know how to post a picture so I tried my best to describe my question in words. X is horizontal, Y is vertical and there is no gravity effect. There is a block is sandwiched by 2 surfaces (top surface and bottom surface). Both surfaces are fixed in X direction and the bottom surface is...
  2. Heisenberg7

    B Why Does Hooke's Law Use a Negative Sign in Scalar Form?

    Assume that we have a block connected to a spring. Also, assume that there is no friction, the spring is massless and ideal. If we were to pull on the block with some force ##\vec{F_{pull}}##, we are going to get the spring force ##\vec{F_{s}}## in the opposite direction. Assume that we are...
  3. T

    Dynamics of a Block on top of a slab with friction between them

    I need to determine: 1) The accelerations of both the slab and the block, the moment right after the spring was released. => I can consider Fspring as a constant force. Both bodies can be considered as points of mass. I'm taking as positive the left direction. I've analyzed both objects using...
  4. T

    Energy analysis of this system (curved ramp up and a spring)

    For point one it's clear that I have to use energy => ##ΔE_{AB} = W_{friction}## ; ##\frac 1 2 mv_0^2 - \frac 1 2 mv_1^2 = mgμ_d d## After that there is the path BC, but I don't know how to analyze it from an energetic standpoint. Then after BC the block will now have a different velocity, I...
  5. S

    Find the coefficient of friction between block and surface

    Ff.x= mv2/2 - kx2/2 umgx= mv2/2-kx2/2 u= mv2-kx2/2mgx =
  6. N

    Block and wedge problem -- Where am I going wrong?

    This question is from the book Kleppner and Kolenkow Q 3.8: ___________________________________ My attempt is posted here: ___________________________________ The value of a(minimum) that I'm getting is different from the official solution. The official solution is posted here...
  7. Sep

    B Rotational Dynamics: Confused about the tension in this string pulling a mass up an incline

    Question A wheel of radius r and moment of inertia I about its axis is fixed at the top of an inclined plane of inclination θ as shown in the figure. A string is wrapped round the wheel and its free end supports a block of mass M which can slide on the plane. Initially, the wheel is rotating at...
  8. M

    Lagrange equation for block and incline

    For this problem, Does someone please know where the term highlighted in blue came from? Thanks!
  9. M

    Lagrangian of a block on an inclined plane

    For this problem, I am confused where they get these two terms from Can someone please explain? I get all the other terms expect those. Thanks alot!
  10. hello478

    Horizontal force by block on a beam

  11. chwala

    Find the value of ##θ## and frictional force acting on the block.

    Refreshing on this...This is a relatively new area to me ...my solutions should be correct...what i am trying to engage on is if there are any other ways of looking at the same problem. Ok in my working i have, ##30 + 35 \cos β-45=0## ##\cos β=0.4286## ##β = 64.62^0, ⇒θ=25.4^0 ## to one...
  12. chwala

    Calculate acceleration and speed of block

    Pretty straight forward, ...reason of posting is to check why i am having a negative value for ##a##. From my study, i know that ##R(||)## to plane ##F - 40 \cos \dfrac{π}{3} = 4a## ##a = -5 m/s^2## or can i as well have the equation ( friction and tension are at equilibrium) as, ##40...
  13. abrogard

    B What forces are required to tumble a block?

    I just want to know how strong I have to be to move a large stone block by tumbling it over. A formula is what I'm looking for I guess. Assume a perfect cube. Begin with a raised edge making say 10 degree angle with the ground. I get my fingers in there and start lifting. I suppose when I get to...
  14. L

    Block on slope. Different answers using energy vs forces

    The first equation is when I use forces. The block is in static equilibrium, therefore the spring force should balance the gravitational force. The second equation is when I use energy principles. Energy before compression = Energy at compression. The height before is x * sintheta, and the...
  15. S

    Point particle model for a person pushing a block on ice

    a) For the model, I'm not sure how to include all the forces I think are present. Gravity, normal force from the ice, contact force from ice to person, and person to ice. Is there also a normal force keeping the person's hands from going "into" the ice? b) As for part b, I would think to use...
  16. Memo

    Pulling a block along a surface using a string inclined at an angle

  17. yashboi123

    Force exerted on block B by Block A when being pushed on a frictionless surface

    I was just wondering why you would do mB * a to get the force A is exerting on B instead of mA * a
  18. Y

    How to prevent being blocked when I use VPN?

    I use Norton protection. They offer VPN. I try to use it. But I was blocked by a site after I use the VPN. I had to turn VPN off to get to the site. Why? and what can I do to resolve this and still use VPN? Thanks
  19. R

    Problem about a block of ice melting (specific latent heat)

    Energy lost by water = Energy gained by ice Energy lost by water = 0.16 x 4200 x (100-t) Energy gained by ice = 0.205 x L + 0.205 x (t) (where t is the temperature at thermal equilibrium). However, there does not appear to be enough info to continue. The solution, however, considered t to be...
  20. A

    Block and pulley on movable incline

    This was the question: I derived the equations as mentioned in the relevant equations. But I could not solve the equations to find the answer. I realise with respect to inclined plane the acceleration must be a since string cannot slack. With respect to ground, the acceleration of incline is...
  21. A

    Oven controller block diagram, transfer function and temperature calcs

    FIGURE 5 shows an electrically heated oven and its associated control circuitry. The current, I, to the oven's heating element is fed from a voltage-controlled power amplifier such that I = EK1. A voltage, VD, derived from a potentiometer, sets the desired oven temperature, TD. The oven...
  22. T

    How do websites block unauthorized requests?

    If I say run the httr library on R and send DELETE or PUT or POST requests to a website, can it alter the contents and display of the webpage or do we devs have methods to block requests from unidentified sources. E.g if I send a DELETE request to Physics Forums website does it mean I can take...
  23. Simon Peach

    B What is the building block of maths?

    Sets are called the building block of maths, but why? To me sets are a collection of 'things'. Were as numbers are what give the 'things' a meaning. Myself I think that addition is the building block and maybe subtraction, all the other processes, addition and division are only quick ways of...
  24. A

    Solving the Basic Mechanics Bullet Block Collision Problem

    $$ \frac{5E-3*v^2}{2} = (2 + 5E-3)(10)(0.2)(2) $$ v = 56.64 I just don't get how this is the wrong answer....it's just simple conservation of energy, right?
  25. E

    Exploring Mental Blocks in Mathematics: A Personal Perspective

    Since this is a "general lounge" area, I will assume this rather personal story is not out of line. I am 64 years old (relevance of my age should become clear shortly) and graduated from an Ivy League University in 1980 with a degree in Electrical Engineering. I also scored over 700 on my math...
  26. H

    Finding the work done by a block

    We want to figure out how much work friction does on a block as it slides down an inclined plane with a rough surface. we find the force due to gravity that pulls the block down the ramp, that's found by M * g * sin(θ), The normal force on the block is given by M * g * cos(θ). The force of...
  27. L

    Find speed of block using energy and spring equations? Help please

    So here's what I did but it isn't right: W = (Kf + Uf) - (Ki + Ui) (2.6)(9.81)(0.45)(-0.01)=(1/2mvf^2 + 1/2kxf^2) - (1/2mvi^2 + 1/2kxi^2) -0.1 = (1/2(2.6)(vf^2) + 1/2(855)(0.02^2)) - (1/2(855)(0.03^2)) 1.3Vf^2 = 0.114 Vf^2 = 0.09 Vf = 0.3 m/s
  28. MatinSAR

    Forces acting on a block that is pushed against a wall

    Picture of problem: For the object to be moving, it must overcome friction. ##f=0.5*0.6F = 0.3F## ##mg=22N## Upward motion: ##0.8F>mg+f \rightarrow 0.5F>22 \rightarrow F>44N ## Downward motion: ##0.8F+f<mg \rightarrow 1.1F<22 \rightarrow F<20N ## I think correct option is D. Can you please...
  29. A

    Friction, Mass and Acceleration: Analyzing Block Motion

    The block starts to slide if friction can no longer hold the block. F=u*n and F=(m1+m2)a so: (m1+m2)a=uN=>am1+am2=uN=>am2=(uN)/(am1) So:am2=(uN)/(am1) is the force. The answer is F=(u*m1g(m1+m2))/m2 I do not see how the acceleration terms are canceled. Is my answer equivalent to this?
  30. paulimerci

    State whether the distance x for the block would be greater/less/same

    I was able to solve for a, b, c, and d. I don't know whether I'm saying it right for part e. The first scenario is a perfectly inelastic collision. After impact, the bullet transfers momentum to the block, causing the block to move (it was initially at rest), and the bullet + block fall at a...
  31. A

    Pistons have cracked and put a hole in the block

    Hi all so I had a injector go on my audi q5 2009 and had a mechanic to put a new injector in it and a Alternator and auxiliary belt so after the work be done I take it for a drive did about 2miles than Start it to make Allowed tapping noise so get hold of mechanic and he's said get it home than...
  32. T

    A Puzzling Equation: Will the Block Slide or Not?

    So far I have reached a pretty promising equation that if uk * g >= F/(m1+m2+…+mn) then kth block will atleast surely not slide wrt the lower one. But the converse to this that if uk * g < … then it will “surely” slide is wrong!! Stuck on this from many days! Thanks (:
  33. iceninja3

    Find acceleration of Moving incline with a block on it

    My attempt: As I need to find acceleration I believe that I need to use F=ma(and thus draw a free body diagram). I drew the block's weight components(mgsinθ, mgcosθ) and concluded that the only force acting on the plane in the horizontal direction is the horizontal component of...
  34. Elaren

    Final velocity of a block on a spring pulled downhill

    Note: wording is ambiguous so I assumed spring started from equilibrium, in which case it stretches as we go downslope. Final height (at lower point on slope) is 0. Distance along slope = Distance the spring stretches = d= ##s_f## = ##2/cos{\theta}## =2.13 Height change = h = ##2 tan{\theta}##...
  35. paulimerci

    How much force does the 20 kg block exert on the 10 kg block?

    The contact force on 10 kg due to 20 kg is taken as Fc2 m1 = 30kg, m2 = 20kg, m3 = 10kg F_A = Applied force μ = 0.15 Net force = mass X acceleration Fc2-Friction force = m3 X a, where a = F_A / (m1 +m2+ m3). Therefore the equation becomes Fc2 = m3 F_A/(m1+m2+m3) + μN = F_A/6 +15 I...
  36. Alaraity

    Static and Kinetic Friction -- Tilting a ramp until a block starts sliding

    None yet
  37. S

    Comp Sci 8 bit block division -- University Level Intro Course: Networking

    What I think I should do: 1 = 0001 7 = 0111 3 = 0011 First block = 00010111 Second Block = 00110000 Now, I do binary division 00010111/11010 = find the answer 00110000/11010 = find the answer This is what I think I should do, but I am not sure if this is correct. Is this basically CRC? Any...
  38. J

    Pushing on a spring connected to a block

    For the second force with the spring, I know the spring force will exert a force back on my hand, for example, but I'm confused whether the applied force is transmitted unchanged to the block or whether it will decrease because of the opposite spring force. What happens to the block when the...
  39. Rikudo

    What Determines the Direction of Motion in a Plank and Spring System?

    I don't understand the question. If it want the mass to stop and reverse its direction, then does that not means ##vo## can be anything? (obviously not 0 since it will make the system not moving at all).
  40. P

    Static Friction Question — A wood block sliding on a tabletop

    I have no idea how to start this other than that I think that Fn is 17.64N and Fnet is 0. But I don't have the mew, so I am not sure how I am going to get the force of static friction.
  41. A

    I Block with upward velocity tethered to a bottom block

    If I shoot a block with mass m1 with initial velocity v, and the block m1 goes to the end of the string tethered to the bottom block with m2 without lifting it up, what is the force equation involved with the block with m1? I am torn between whether it would be 1) -T -m1*g = 0, which I am...
  42. AspiringPhysicist12

    Block of mass M attached to rope of mass m

    We have the string's mass constraint m(x) = m(x/L). The block is accelerated right by force T(x=0) = Ma, where a = F / m + M. But at the point where the force is applied (i.e. x = L), I believe we have m(L/L)a = ma = F - T(L). But this would imply T(L) = F - ma = F - m(F / m + M) = F(M / m + M)...
  43. AspiringPhysicist12

    Block on an accelerating wedge (part c only)

    My solution for part b) (i.e. minimum acceleration) in case it's needed: https://ibb.co/D8CCQMM I'm confused about part c. 1) Since the block will travel up the incline if a > a_max, acos(theta) is up the incline. But based on my attached FBD diagram, acos(theta) should be down the incline...
  44. ols500

    Linking moments with friction force for a sliding block

    Hi so with this question, I am really confused. Even from the start. Like it doesn't tell us where the force is acting on. From top of block, middle of block etc? And I know how to determine the direction of moment for something on a pivot, not in this scenario though. The answer is A. They did...
  45. rudransh verma

    Accelerating wedge with a block at rest on it

    I have drawn a fbd and the logic I think is that at rest the block moves down the wedge but when a force P is applied vertical force becomes zero and the horizontal force ##F_N\sin \beta## = P?
  46. Y

    How Do Spring Force, Static Friction, and Normal Force Interact?

    i would like to understand why my answer is incorrect and how i need to solve this problem
  47. N

    A-level Maths Mechanics: Prevent Block from Sliding Down Inclined Plane

    The best I could do was draw a forces diagram. I know that friction would be working up when the block is on the point of slipping down the plane and friction will be acting down the slope against the direction of motion when the block is on the point of slipping up the slope. (not even sure if...
  48. Y

    Preventing a block from sliding down a frictionless inclined plane

    hey i would like to understand something, i solve this question but i don't understand why my answer is right, first of all we learn that in problems like this we need to disassemble into components the mg and that what i try to do here but i didnt get the right answer so then i try to do same...
  49. Shreya

    Momentum Conservation: Bullet enters a block

    I can understand that using conservation of momentum, we can find v. But we need V for that. The equation for V involves h and so we need h. But I am not able to comprehend the equation involving l,h and a. The question doesn't specify what a is. Please be kind to help
  50. shivajikobardan

    Comp Sci Confusion on motion estimation block diagram-MPEG video compression-:

    My doubts are as follows-: -> Why frame n is not segmented to blocks? -> Why no inputs from (n-1) side for block matching? -> What do we do in prediction error coding? Source-: https://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/AV0506/s0561282.pdf I have read this many times but that...
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