How to dilate a Body & let it 'kick' another body？

[finscn]

I change the radius of a circle quickly ， I want to it could kick other bodies.

But I found the power/force of the circle is too small.

How can I do that : if the radius of a circle change slowly , the power is small; if dilated quickly , the power is big ?

[schteppe]

Hi. The radius of a circle does not have dynamics, which means that it doesn't use velocity or force to update itself. It's assumed to be constant. In fact, the definition of "rigid body physics" states that geometry should be rigid and not change...

This said, you'll have to apply the needed forces or pulses manually. You could get the contact normal and use that to compute the "kick force"..

[finscn]

Thanks .

Another question : if I've computed the "kick force" , how to apply to the body which will be kicked?

Use appleForce or applyImpulse ? What's different between them?

Thank you very much.

[schteppe]

@finscn .applyForce is usually used to add forces during a longer time (for example gravity or springs), while .applyImpulse is used to add an instantaneous "kick" to an object (for example when hitting a ball with a baseball bat). To me it sounds like you want .applyImpulse()

[finscn]

Yes. Thanks very much!