MIT Physics Demo -- Potential Energy to Kinetic Energy

[ceNorene189]

:)yeppp

[dayspeace]

Woah.. this is cool, I really though the result that could be gotten from the two balls would be different, but the result of the experiment proved otherwise. I thought the it would have a significant difference because the other was hooked with a string and the other not. It is nice and very informative, nice video.

[emeemmanuel]

I think its measuring time because the photo gates are placed in the same position. As mentioned before, think of vertical and horizontal components separately, gravity is the only one affecting the vertical direction thus they should reach the same vertical position at the same time. Its like the example of shooting the cannonball horizontally-- it will reach the ground at the same times if the cannon was simply dropped.

[chemlink1]

I would like permission to use this video in my science classes. I appreciate your consideration.

[cheerklk89]

So, I typed kenetic energy in the search bar to get a BASIC understanding of the definition for my physical science class. I guess I should have read the part of the video labeled "MIT Physics"....ill be back to this video after I get my PhD, which I am guessing will be in about 10 years.

[polarautumn]

(oops, ran out of room)...

And, since t=d/v, t=(0.04m)/(4.429m/s)=0.0091sec­onds. It works out nicely. ;)

[polarautumn]

I'm almost positive the units of the photogate are in seconds: (0.0091seconds). The photogates are measuring the time for the diameter of the ball to pass by the photogate. The balls diameter is about 0.04 meters (same as 4.0cm) and it passed through the p-gate at 4.429m/s if dropped from 1 meter. Ek = Ep, so 1/2mv^2 = mgh. Mass cancels out, so we have 1/2v^2=gh where g is acceleration of gravity at 9.81m/s^2 and h is height. So, v=sqrt(2gh). v=sqrt[2(9.81m/s^2)(1m)] = 4.429m/s. And, since t=d/

[polarautumn]

What are the photogates measuring - time or speed? 0.0091 (units??)

[davsone]

Second one should go longer if distance is the same. It goes under lower acceleration becouse the string "takes" some of the gravity acceleration. It is my point of view.

[aliyoop3]

very enlightening. Thank you 

[Maxuras]

Yes, I was confused about this, too. I thought: Hey, that second thing is supposed to be slower, why does it take 0.091 in both cases ...

... Oh wait, that thing does not measure the dropping time, it measures the speed at ground level. - Yeah, now it makes sense.

[betiuxyricky]

@Maxuras right thank you!

[yogibret]

@Maxuras Thanks for the clarification. I was confused too.

[ajskilton]

@Maxuras think about vertical and horizontal motions separately and I mean separately!!

[sroyle01]

love the idea but please try it from 100 meters

[jbignes5]

Seeing that both nodes, time points are equal there should be no difference and there wasn't. This was to show that two methods of dropping did not slow the time it took to get the same distance. This was to show that "Gravity" is constant. Even when the methods differ the speed of the ball is faster in the second method but takes the same time to get there. But only slightly faster due to the string.

[gennaman2bit]

@jbignes5 Absolutely wrong, the speed of the ball is exactly the same, the string changes only the direction of the ball (vertical to horizontal) but the speed have same modulus. in 1st try we have full vertical speed, in the 2nd we have no vertical speed (we are in the lower step of the pendulus, vertical speed is converted to horizontal speed due to the string. As u can see, the time of dark picked up by the photo gate is the same, that means same speed (same modulus)

[shriramvenu]

@gennaman2bit actually its circular motion not vertical or horizontal.. speed is purely horizontal exactly at the photogate, which is when the angle of the string is 0 degrees (ie straight down) if left to right is -90<angle<90

[gennaman2bit]

@shriramvenu are u kidding me? U said speed is purely horizontal at the photogate, that's what i said.

[LouSaydus]

*smack* oops..

[bjstechbjstech]

Hi very ambitious technology. However my only question is. In your 2nd demonstration, i believe the metal ball is magnetized by holder and passing through - + rods/Multi-meter will create energy. No different to an alternator correct?

[yogibret]

according to my timer, the pendulum takes longer, but that would make sense since the string is acting to oppose the force of gravity and at the bottom of the swing the force is entirely pulling upwards - perpidicular from the velocity.

[yogibret]

It would take pi/2 times longer or 57% longer than the free fall since that is the added length of the arc.

[fredrikhcs]

wrong

[betiuxyricky]

@yogibret you dumb ass read the description its not talking about how long it takes the ball to fall, its talking about the velocity (acceleration) (gravity is an example because it increases the speed of objects every second)

[crippled82]

in other words: gravity is conservative?

[MarkTwist20]

Great experiment. You should repeat the test with Milkovic's pendulum - veljkomilkovic(dot)com

Check out these YouTube videos: "Testing Large Milkovic 2 Stage Oscillator Video 6" or

Veljko Milkovic - Hand water pump with a pendulum" or

"Veljko Milkovic - Laboratory pump with a pendulum".

I'm wondering what kind of results you will get in that case?!

[crippled82]

:P

they don't like devices that challenge thermodynamic laws

[700]

plz use formulas too.

[pashaahsj]

well its just its just

ut+1/2gt^2

for both drops as the horizontal velocity does not matter

[muchadoaboutnothingg]

displacement = ut + 0.5at^2

as for KE = PE:

0.5mv^2 = mgh (or GMm/r^2)

[muchadoaboutnothingg]

and as for the above experiment,

the initial velocity is 0, making s=0.5at^2 where a is gravitational field

anyways, you don't use this formula to deal with the above experiment, you use PE loss = KE gain

[pashaahsj]

OH ! thats correct.

I made this same mistake in my physics mock !!

used SUVAT !! for a skateboarder coming down a parabolic ramp :(

i assumed that its similar to projectile motion !

whereas, its not, the horixontal V changes too !!

thanks anyway !

[feruwehr]

Ye but the main formual for KE is E=mv^/2 and for PE E=mgh, but it depends on which height is the ball and from which starting point does it start.And since we don't have speed then we use 2gh.