Interactive Physics^TM

Giving an Object a Particular Acceleration

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I am trying to simulate a kinematical situation in which an object is supposed to have a particular acceleration, say 5 m/s². How do I do this in Interactive Physics^TM?

There are at least a couple of convenient ways.

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The "Physicist's Way"

The method that springs to the mind of a physicist is "Use Newton's Second Law!"

• Give the object to be accelerated a mass of 1.0 kg (Properties Window).
• Create a force () in the direction that you want to accelerate the object.
• Set the magnitude of the force equal to the amount of acceleration you want (using the force's Properties Window).
• You can make the force invisible, if it bothers you, using the Appearance Window - just uncheck "Show".

If, for some reason, you can't make the mass of your object equal to 1.0 kg, simply use Newton's Second Law - F_net = ma (m = mass of the object, a = its acceleration) to calculate the force you need.

Here is an example.

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The Other Way

The object shown below will have an acceleration of 5 m/s in the x-direction. It will not be affected by any gravitational forces.

It turns out that the Interactive Physics^TM' Anchor Tool () has the effect of removing the object that it is attached to from normal force and acceleration calculations in the simulation. This property can be exploited, with the use of formulas, to make an object do just about anything - from following an arbitrary path, to having a particular acceleration. To do this:

• Attach an anchor () to the object that you want to accelerate.
• Open the Properties Window of the object you want to accelerate.
• In the Vx and/or Vy fields, enter "(whatever acceleration you want)*time".
• You can make the anchor invisible, if you wish, by unchecking "Show" in its Appearance Window.