# What is Seconds: Definition and 123 Discussions

The second (symbol: s, abbreviation: sec) is the base unit of time in the International System of Units (SI) (French: Système International d’unités), commonly understood and historically defined as 1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each. Analog clocks and watches often have sixty tick marks on their faces, representing seconds (and minutes), and a "second hand" to mark the passage of time in seconds. Digital clocks and watches often have a two-digit seconds counter. The second is also part of several other units of measurement like meters per second for speed, meters per second per second for acceleration, and cycles per second for frequency.

Although the historical definition of the unit was based on this division of the Earth's rotation cycle, the formal definition in the International System of Units (SI) is a much steadier timekeeper:The second is defined as being equal to the time duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the fundamental unperturbed ground-state of the caesium-133 atom.
Because the Earth's rotation varies and is also slowing ever so slightly, a leap second is added at irregular intervals to clock time to keep clocks in sync with Earth's rotation.
Multiples of seconds are usually counted in hours and minutes. Fractions of a second are usually counted in tenths or hundredths. In scientific work, small fractions of a second are counted in milliseconds (thousandths), microseconds (millionths), nanoseconds (billionths), and sometimes smaller units of a second. An everyday experience with small fractions of a second is a 1-gigahertz microprocessor which has a cycle time of 1 nanosecond. Camera shutter speeds are often expressed in fractions of a second, such as 1⁄30 second or 1⁄1000 second.
Sexagesimal divisions of the day from a calendar based on astronomical observation have existed since the third millennium BC, though they were not seconds as we know them today. Small divisions of time could not be measured back then, so such divisions were mathematically derived. The first timekeepers that could count seconds accurately were pendulum clocks invented in the 17th century. Starting in the 1950s, atomic clocks became better timekeepers than Earth's rotation, and they continue to set the standard today.

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1. ### B How to Add Metres & Seconds for Equal ds2: Einstein's Theory

Reading this PDF from Professor Richard Conn Henry, I am confused by the multiplication by c on page 2. x, y and z are metres. t has units seconds. So I would think, "We can't subtract seconds from metres , we can't subtract dt from dx." To sidestep that, Einstein multiplied dt by c. c has...
2. ### Distance traveled by a Ball affected by friction after t seconds

Hi everyone, i have been trying to find an answer to this problem I have but couldnt find any good answers... (I dont know much about this stuff, but need a formula for a Project I am currently working on). So The problem goes as follows: Assuming we have a ball with a mass of m which is...
3. ### Time Dilation in the ISS: 2 Seconds in a Year

Using the above formula I get that the time goes 6.5∗10−86.5∗10−8 percent faster in ISS. Thus, this is approximately 2 seconds in a year. But the answer is much lower. Where am I making a mistake?
4. ### [Ohm's law] Why does the answer key use the time after 5 seconds?

This the answer key:: im confused because it say "how much energy has been dissipated after 5s". So shouldn't you be looking at the ground after 5 sec. but apparently the solution look at it before 5 sec, am I missing anything, can someone explain
5. ### Calculate the time to reach the floor in seconds

r = 0.25m I = 7.14kgm^2 h = 6.01m Ei = Ef mgh = 1/2mv^2 + 1/2Iw^2 2mgh = mv^2 + I(v^2/r^2) 2(35.8)(9.81)(6.01) = 35.8v^2 + 114.24v^2 v = 5.304 m/s v = d/t 5.304 = 6.01/t t = 1.133 (The correct answer is 2.2673. What did I do wrong?)
6. ### B Fewer seconds or shorter seconds?

In the twin experiment, the travel time is shorter for the traveling brother than for the static brother. Since the unit of time in physics is the second, is the travel duration shorter because: (1) it contains fewer seconds or (2) the number of seconds is the same for both brothers but the...
7. ### Scientific analysis -- How many seconds does it take for the paper to burn?

I have a problem: in the same anime I saw that Senku estimated the time to start burning the paper in sixty seconds, one minute and with a lens. The data is as follows: The lens he used has a diameter of 5 centimeters. The solar constant, assuming it is the same as 3700 years ago, is 1362 watts...
8. ### Velocity after t seconds with a time varying Force

Figure given in question-: I first found out the time when force will be equal ro friction.After force becomes equal to friction there will be no acceleartion further,so velocity after that time will be same.I calculated the velocity by getting a relation of it with time.I got the velocity as...
9. ### In how many seconds will the n-th wagon pass next to me?

Homework Statement Train starts to travel in a straight line at increasing speeds. The first wagon passes next to me in 4 seconds. In how many seconds will the n-th wagon pass next to me? Homework Equations s= vo.t + 1/2at^2 v= vo + at The Attempt at a Solution First of all we didn't learn...
10. ### MHB [ASK] Determine its velocity and direction after √(3)/2 seconds

Something was thrown with an elevation angle 60^{\circ}. Determine its velocity and direction after: a. \frac{1}{2}\sqrt3 second b. \sqrt3 second I tried solving the (a) question by substituting the angle to the equation y=v_0\sin\alpha t-\frac{1}{2}gt^2 and got 0 (the book uses 10m/s^2 as the...
11. ### Unit conversion meters Newtons years seconds

Hi, I need to convert a value of 12*10-16 m7 N-3 y-1 to the units of kPa-3 m2 s-1. Can anyone help me? where: m = meters, N = Newton, y = year, s = seconds. Thanks!
12. ### MHB How far will the car travel in 10 seconds

$\tiny{Embry-Brittle \, 12}$ $\textsf{A car, starting from rest, accelerates in a straight line at a constant rate of$\displaystyle 2.0 \frac{m}{s^2}$}$$\textit{How far will the car travel in$10$seconds}$\begin{align*}\displaystyle \Delta t&=10\\ a&=2\\ d_i&=0\\ v_i&=0\\...
13. ### Energy absorbed by the inductor in 4 seconds

Homework Statement Homework Equations V = L di/dt Energy = V*I*t The Attempt at a Solution First we find out V across L This V will be there only for 1st 2 seconds as after that there is no change in current. So V(across L) is L * di/dt = 2 * 6/2 = 6V equation 1 Now Current is a function...
14. ### MHB Radians to Degrees, Minutes, Seconds

Reduce the following numbers of radians to degrees, minutes, and seconds. (a). 0.47623. (b). 0.25412. Can someone work out (a) in steps? I can then use it as a guide to solve (b).
15. ### MHB Minutes, Degrees, Seconds to Radians

Express the following angle in radians. 12 degrees, 28 minutes, 4 seconds that is, 12° 28' 4". I cannot apply pi/180° to this problem.
16. ### How many Photons per second are entering the pupil?

Homework Statement (a)Estimate the number of photons per second emitted by a 100-W lightbulb, assuming a photon wavelength of 550nm.(b) A person can just see this bulb for a distance of 800m, with the pupil dilated to 7.5mm. How many photons per second are entering the pupil? Homework...
17. ### Projectile motion: equal distances in 5th and 6th seconds of trajectory

Homework Statement With what speed should a body be thrown upward so the distance traversed in the 5th second and 6th second are equal? Homework Equations No idea since I fail to comprehend the statement of the problem. The Attempt at a Solution This doesn't make sense to me, the distance...
18. ### What Angle Maximizes Air Time for a 34.6m Football Punt?

Homework Statement A football punter can punt a maximum range of 40.8 m. If he instead wants to punt only 34.6 m, but maximize the time the ball is in the air, at what angle from the horizontal should he kick the ball, and how long will it stay in the air if he hits it perfectly? (neglect air...
19. ### Find the angular speed at t=3 seconds

Homework Statement A shaft is turning at 65.0 rad/s at time zero. Thereafter, its angular acceleration is given by α = -10 rad/s 2 - 5t rad/s 3 where t is the elapsed time. (a) Find its angular speed at t = 3.00 s. (b) How far does it turn in the 3.00 s seconds? t=3 seconds wi= 65.0 rad/s α =...
20. ### Why is my video blurry for 5 seconds?

I have a video to present to my class and for five seconds it goes all blurry. Does anyone know how to sort it out and why it happened?
21. ### Find the speed of the object after 4 seconds

Homework Statement An object is thrown horizontally and after 3 seconds the speed vector forms the angle pi/4 radians with the horizontal direction. FInd the speed after 4 seconds. Homework Equations v=gt The Attempt at a Solution As it forms the angle pi/4 radians, vx=vy, so v0=gt=3*10=30 vy...
22. ### Find the speed of the particle after 0.2 seconds

Homework Statement The particle is thrown horizontally with speed 10 m/S (I believe from a height). Find the speed of it after 0.2 seconds. Homework Equations vx=v vy=gt v=sqrt(vx^2+vy^2)[/B] The Attempt at a Solution vx=10 vy=10*0.2=2 v=sqrt(100+4)=10.198m/S Am i right?
23. ### When I lit a laser ray for 10 seconds from a distant planet

I am on Alpha 4 light years away from earth. On 1st Jan, 2016 I lit a powerful laser light towards Earth for 10 seconds and then switched it off. My friend on Earth knows that he has to detect that light after 4 years on the night of 1st Jan, 2020 from a space station using a very powerful...
24. ### Functions in C to calculate hours, minutes, seconds from milliseconds input

Homework Statement Write three functions int get_hour(int timestamp), int get_min(int timestamp), int get_second(int timestamp) which will respectively return the hour of the day, the minute of the hour, and the second of the minute from a value given as parameter which is in milliseconds...
25. ### What frequency did you hear 3 seconds after police pass?

Homework Statement The police was headed to a felony and passed you so you stopped. What frequency did you hear 3 second after the police passed you? Homework Equations f=1/T The Attempt at a Solution f=1/3 f=.33Hz
26. ### Heat-shield for a Mach 30 missile at 10km for 10 seconds?

Using an ablative carbon-carbon heat-shield, what thickness would be used up? Or might a ceramic insulator be able to handle it? What would happen if the nose was solid aluminium?How can this be calculated? What information do I need to figure this out?
27. ### James Jumps: Calculating the Fall in Seconds & Meters

Homework Statement To escape the fire which has just declared itself in the building, James jumps through the window. One second before reaching the mattress, he traveled half of the height of fall. What is the total time of the fall in seconds ? What is the total height of the fall in meters...
28. ### How fast is ball thrown up to come down in 2 seconds

Homework Statement Ignoring air drag, how fast must you toss a ball straight up for it to take 2 seconds to return to same level you threw it from. 1. 20 m/s 2. 7.5 m/s 3. 15 m/s 4. 5 m/s 5. 10 m/s Homework Equations vf = vi + a x t The Attempt at a Solution To me this problem seems...
29. ### Adding Degrees Minutes Seconds

Homework Statement (42°12'13'')+(59°56'15'')+(257°51'35'') Homework EquationsThe Attempt at a Solution 42°12'13'' 59°56'15'' 257°51'35'' -------------- 358°228'63'' +3° +1' -60'' --------------- 361°229'3'' -180' --------------- 361°49'3'' The answer is 360°0'3'' Where did I go wrong?
30. ### Energy unit to kelvin, seconds, density, length

Homework Statement Convert 1 ##Gev## to Kelvin, and convert ##GeV^{-1}## to meters, seconds, and convert ##GeV^4## to density ##(kg/ m^3).## Homework Equations natural units ##c=h=k_B=1## The Attempt at a Solution I know to convert energy to meters, I can use ##\lambda =hc/E##, I get the...
31. ### How many seconds will it take before the cars meet?

Homework Statement Two cars are initially 17.50 km apart on a straight road. If the cars are moving toward each other, car 1 with a speed of 7.50 m/s and car 2 with a speed of 10.40 m/s, how many seconds will it take before the cars meet? Round your answer to three significant figures...
32. ### How is average power calculated using volt-seconds and RMS voltage?

If I have a voltage magnitude that I can modify, say I'm measureing the RMS of it. And that it is at a set frequency, and I want to know the quantity (that I am only just familiarising myself with) known as volt-seconds, on a coil and magnetic core. Say I was looking at how many volt seconds the...
33. ### Unusual Patient -- Pulse Pressure Varying Every Few Seconds

As part of an EMT shift at an athletic event yesterday, I took vitals on a 45y/o female Pt who had completed the stressful event about 30 minutes prior. She is very fit and experienced in athletic competition. When I was auscultating her BP, I thought that it sounded like she was skipping some...
34. ### MHB Sand Pile Growth Rate: 10 Seconds After Falling

Sand falls on to horizontal ground at the rate of 9m^3 per minute and forms a heap in the shape of a right circular cone with vertical angle 60^{\circ}. Show that 10 seconds after the sand begins to fall, the rate at which the radius of the base of the pile is increasing is...
35. ### Wavelength, period of vibration in seconds

< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > Okay, I am having trouble with the units. I have the values for the wavenumber and I am trying to find the period. These are the formulas that I am trying. T = 1/f ; f = c/lambda example...
36. ### How far bullet travels in 2,5 seconds

I am solving some problems of my physics book for fun and for some reason I am getting a wrong answer from this one. 1. Homework Statement A bullet is shot at an angle of 35o with a speed of 90 m/s. I assume that air resistance is ignored. Calculate bullet's distance from launch site 2,5...
37. D

### MHB How to Calculate Cube Root of a Number in 10 Seconds

The first and the most important step is to memorize the cubes of 1 to 9. These would form an important part of your toolkit in solving the cube roots. Here is a table for your convenience. 1 –> 1 2 –> 8 3 –> 27 4 –> 64 5 –> 125 6 –> 216 7 –> 343 8 –> 512 9 –> 729 Once you memorize this list...
38. ### How long will it take cars to overtake?

Homework Statement A car starts from rest and accelerates uniformly at 3.0 m/s2. A second car starts from rest 6.0 s later at the same point and accelerates uniformly at 5.0 m/s2. How long does it take the second car to overtake the first car? Homework EquationsThe Attempt at a Solution So let...
39. ### How can I think of rotational diffusion inverse seconds?

When thinking of a spherical shaped particle moving about under Brownian motion, one describes its motion by Diffusion. The units being \frac{m^2}{s} I can understand this physically as a distance it will travel from a certain point in space averaged over x-y and z direction. Now rotational...
40. ### Reaching the Moon in 0.9 Seconds: A Physics Challenge

Homework Statement Nothing travels faster than light, which manages to get to the moon from the Earth in 1 second. However, we can still get there in a shorter amount of time. How fast would we have to travel to reach the moon in 0.9 seconds? Homework Equations I know the question is weird but...
41. ### Why do fusion reactors only work for a few seconds?

Hi! I wonder why it is so hard to make a fusion reaction last for more than a few seconds. I have read a few elementary courses in Plasma Physics but do not remember so much. What I do rememeber is that they said that whenever a fusion reaction starts within a Tokamak the plasma tends...
42. ### Pulse powder delivery of 0.25mg for a few seconds

Hi, I am trying to create a laboratory scale system, where I would like to deliver 0.25 mg of a substance which is granular and powder like consistency. I would like to pulse it for a few seconds and stop it. Can anybody tell me a good delivery mechanism for this. I have a method to disperse...
43. ### Convert Radians to Seconds - Solve f(t)=Rsin(ωt + θ)

Homework Statement Given an equation such as f(t)=Rsin(ωt + θ) find the value of f(t) when t=5s Homework Equations N/A The Attempt at a Solution What I'm not understanding is that generally a function sin(ωt + θ) describes what happens when the angle t changes. However the...
44. ### I on finding seconds from maximum height.

A human cannonball was fired from a cannon with a muzzle velocity of 107 km/h. The firing angle was 45 degrees from the horizontal Ive converted 107 km/h to 29.71 m/s 1.How many seconds did it take for the human cannonball to reach maximum height? 2.How high did he rise? h =...
45. ### Dumb integral question, can be answered (or hinted) in 2 seconds no doubt.

Homework Statement Ok, so I am doing areas between curves, but one of the functions is y=50/(25+x^2) This is stupid, but I THINK I am having trouble finding the anti-derivative (I just know my final answer is wrong, but I'm pretty sure it is related to this.) The Attempt at a...
46. ### Need quick help with Series, it will only take a few seconds

So the differential equation I have to solve using power series is y''-xy=0 when x0 = -1 So i set it up Ʃ(n+2)(n+1)an+2(x+1)n - x Ʃ an(x+1)n I know how to generally solve equations like this, but I never solved one like this, where I have to distribute the x ... x(x+1)n ... I just...
47. ### How to Calculate Power Required to Keep a Car Stationary on a Steep Hill?

Homework Statement You are in a car that is on the top of a steep 500 meter high hill. You are stepping of the brakes so your car is not moving. How much energy per second( power) must be expended to keep the car stationary Homework Equations The Attempt at a Solution
48. ### Is there a delay of 1 or 2 seconds in generation of back emf in a dc motor

Does the back emf in a dc motor start to appear after a slight delay(say 1 or 2 seconds) after starting up the motor? I have had this simple doubt for a long time.According to the "generator principle" both applied emf and back emf will always exist simultaneously.Also it would be in violation...
49. ### Equation z = ct + d, z is measured in meters and t in seconds; dimensions of D?

Homework Statement In the equation z = ct + d, z is measured in meters and t is measured in seconds. What are the dimensions (units) of d? answer options are... s/m, m/s, m, s, m*sHomework Equations The Attempt at a Solution plugged in m for z, s for t, and m/s for c. solved for D and got 0.
50. ### Simple Harmonic Motion: Displacement after s seconds

The question is: A 56.0 kg bungy-jumper hangs suspended from her bungy-cord, at rest. She is displaced from this position by 15.0 m downward, and then released. She bounces up and down, with a period of 5.800 s. Assume the woman undergoes simple harmonic motion, described by y(t) = X cos(2...