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I am trying to complete a blender animation where a ball rolls down a slope under the influence of gravity.

To simulate gravity I have calculated the time and distance the ball needs to travel to accomplish an acceleration of 10 m/s^2.

However, I want the transition from the flat part of the slope to be seamless, but the ball seems to suddenly slow down, as you can see from the graph editor.

How do I make the ball act the way that I want? I have used the interpolation type quadratic.enter image description here

enter image description here

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    $\begingroup$ There is a much simpler way if you just want to roll a ball down a hill...Rigid bodies would make things much easier. $\endgroup$
    – Timaroberts
    Commented Jan 1, 2021 at 22:29
  • $\begingroup$ Unfortunately, I have no idea how to use rigid bodies, though it was something that I thought of. If they are very simple and don't require much learning, then that could be an option. Do you have some sort of basic tutorial? $\endgroup$
    – Sid
    Commented Jan 1, 2021 at 22:45
  • $\begingroup$ See my answer, maybe it helps.. $\endgroup$
    – Timaroberts
    Commented Jan 1, 2021 at 22:50
  • $\begingroup$ The ball should never reach the acceleration of 9.81 m/s^2. Even if the ball falls completely vertically, as long as there's some significant friction in neighboring surface causing the ball's angular acceleration, it's some of the potential energy converted to kinetic energy elsewhere than to the ball's falling speed. $\endgroup$
    – Markus von Broady
    Commented Mar 19, 2021 at 8:29

2 Answers 2

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An easier way to roll a ball downhill is to use rigid bodies. This way, the active objects are subject to the scene gravity.

enter image description here

For this, you will want two rigid bodies, one active and one passive. The active one will be the ball, the passive will be slope.

Add rigid body physics to each object in the physics tab:

enter image description here

These are the settings for the ball:

enter image description here

These are the settings for our slope:

enter image description here

A note on the difference between active and passive rigid bodies from the manual

Active

The object is dynamic and is directly controlled by simulation results.

Passive

The object remains static and is directly controlled by animation system, thus does not have Dynamics properties.

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  • $\begingroup$ Thanks for the information, it was helpful. I wished that you would have added how to animate with rigid bodies, as I had to find out how to do that myself, but overall, great solution! $\endgroup$
    – Sid
    Commented Jan 2, 2021 at 20:35
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To modify the vectors that define the curve, you can press the V key (or select Key > Handle type)

That will allow you to align the handles into a straight line, making a smoother transition between two vectors.

enter image description here

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  • $\begingroup$ I wanted the ball rolling to be accurate to how it would behave in the real world. While this solution would work, I don't think it would have been perfectly accurate, and I would have to do a bit of guessing unless there is some way of defining the properties in blender. $\endgroup$
    – Sid
    Commented Jan 2, 2021 at 20:37
  • $\begingroup$ It is indeed easier to do it with physics. For curves you would need to calculate the rate of acceleration to determine the placement for the handles. $\endgroup$
    – susu
    Commented Jan 2, 2021 at 20:41

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