Time to Discuss: Is This Animation’s Result Wrong? ⚠️ Physics of Motion on an Inclined Plane | C4D4U

**Time to Discuss: Is This Animation’s Result Wrong?**
Before you watch: we realize now that our original claim—“the smaller sphere rolls faster”—may have overlooked some critical effects. Think carefully about which forces and energy sinks should be included to get the correct answer:

- **Gravitational Potential → Kinetic Energy:** Δh → v
- **Rotational Inertia & Rotational Kinetic Energy** of a solid sphere
- **Rolling Resistance** (material deformation at the contact patch)
- **Air Resistance** (cross-sectional area vs. mass)
- **Static Friction** (ensuring pure roll, no slipping)
- **Mass Distribution** (how radius affects moment of inertia vs. mass)

We’ve omitted the detailed calculations here—focus instead on *which* terms you’d need to add to your model so that the simulation matches reality.

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💬 **Let’s discuss in the comments:**
1. Which of these effects surprised you most?
2. Are there any other factors you’d include?

“Special thanks to everyone who left feedback in the comments—your suggestions helped us adjust the thumbnail and this description.”

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Why don't I enter the music title anymore.
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I hope for your understanding.

#physics #physicsexperiment #physicseasy

[CDU]

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[buddhiwijayarathna]

when consider the inertia, bigger one has higher inertia. if inertia is high it is more resist to roll or rotate. hence smaller one has high velocity

[Warsaw]

0:26 is when the video actually starts

[prakashdeshpande]

Both of the balls will ( theoretically) have identical increasing velocity during any part of the motion, but under following assumptions :
1) The small difference at the initial levels of the C. G. locations to be negligible.
2) No slipping while rolling.
3) Negligible air resistance.

Now apply the law of mechanical energy conservation. Equate initial P.E. of any ball to it's final K.E. of linear and rotational motion. For the sake of convenience, let the bigger ball have two times the radius of the smaller one. The mass will be eight times. In fact, any other proportion will not make any difference at the conclusion. The terminal velocity of both will come out to be same.
The difference which we see at the video is due to violation of the assumptions mentioned earlier.

[bodybuildhistory]

Lower moment of inertia for the smaller ball and the head start for the smaller ball as well. A ball will fall when the center of the ball has noting beneath it and the center of the small ball is ahead of the center of the large ball at start. But at the end the center of the small ball is further ahead than the initial advantage due to moment of inertia.

[TriumphProjects.]

Initially I thought both the balls will move in same speed. Now its clear to me. Thank you for the video.

[physicsclasswithputisir]

The center of the smaller sphere is little ahead of the larger one, because of the small radius. So it has to travel a smaller distance . So it takes less time.

[bradowen]

The air friction is high on the larger surface area, and the ground friction is also higher in a heavier object.

[kevinhardy]

If falling from the same height straight down in a vacuum, they of course would fall at the same speed. But on an incline, the potential energy of height is converted into kinetic energy AND rotational energy. The larger ball will therefore be slower.

[CorindaJansen]

The small one
I was right!! Pyshic class is not useless 😂
I love this idea!

[sheffd]

Over a long distance, a larger ball will have a higher speed.
As kids, we would roll old tires down a slope. The small diameter tires would accelerate quickly, but then the larger diameter tires would catch up and overtake them.

[marcelchamby]

JUST BOUGHT A EPIPHONE SG SPECIAL AM BLOWN AWAY .... SWEET ACTION AND TONE BEST I HAVE HAD IN 58 YEARS OF PLAYING... GOOD WORK FOR 200 BUCKS

[Downecker]

I just found you! I like what I see! I'm along for the ride!😂😂

[andresurdaneta]

Agradecido por el nivel de conocimiento de los comentaristas.Aprendí un poco de física.😊

[ganeshbhogaraju]

You have shown us what's happening from outside not from inside the balls.Thank you.

[wmchan]

The balls don't "fall down freely". Even if this is done in a vacuum to remove air resistance, because of friction between the balls and the slide, the balls rotate as they travel down. They convert potential energy to two kinds of kinetic energies, i.e. rotational and linear. At any given time, it takes more potential energy to accelerate / rotate the bigger ball than the smaller ball. The bigger ball converts more potential energy to rotational energy than linear energy compares to the smaller ball. As it rotates slower (but carries larger rotational energy) it travels down slower too. Therefore no matter how long the run is, the smaller ball always win. In an imaginary world where there is no friction, the two balls will not rotate and will ""just fall down"" at the same speed.

[JohnH-momb]

The laws of physics give you the answer. In a vacuum, both balls would freely fall at the same speed, because the force of gravity that accelerates them is proportional to their mass, and the “inertia that holds them back“ is also proportional to their mass. In this case, you have additional losses from friction in the air, and rolling friction, both are larger for the bigger ball, therefore it doesn’t accelerate as fast.

[Gardengap]

Why were the two videos uploaded 30 seconds apart?

[kevinlin]

As far as I know, the greater the mass, the more affected it is by the inertia of standing still when accelerating, so the acceleration is slower, right?🤔
Just like the starting speed of a truck is limited by its weight, its maneuverability is not as good as that of a car.

[ColinMill]

This is just a CG not an actual experiment. If it were in a vacuum the balls would have the same speed after the same height loss.
The moment of inertia of a uniform sphere is 0.4mr^2 so, at a given rolling speed the rotational energy will be 0.2mV^2. so the combined linear KE (0.5mV^2) and rotationsl energy will be 0.7mV^2. Note this is independent of the radius of the sphere and proportional to the mass.
So at each point we have mg delta h = 0.7mV^2. the mass cancels out leaving g delta h= 0.7 V^2
Air resistance would cause the larger ball to win due to its lower frontal area to mass ratio.