I am looking for interesting, easy to do experiments to Newton's second law of motion. This is for a high school, so nothing is known about momentum and the law is just $\mathbf{F}=m~\mathbf{a}$.
I found that some people do "crater" experiments dropping objects into flour (see for instance here), however I am still trying to understand how exactly this relates to Newton's law.
As far as I understand all objects dropped from the same height arrive with the same velocity at the flour. The flour provides a force on the object that decelerates it from its velocity down to zero velocity.
If I assume that the force is constant during impact (Does this make sense at all?), I get from Newton's law that the deceleration (absolute value) is smaller for the heavier objects, therefore they leave a deeper impact crater.
Does this sound like a good interpretation of the experiment?
They also mention measuring the width of the crater. How can this be used?
Are there any other (easy to do) experiments related to Newton's second law?
Best Answer
The depth of the crater will depend primarily on three things:
To investigate Newton's 2nd law, you are going to have to keep 1. and 2. constant. That means finding marbles of different mass but the same size -- not easy. Assuming the size of the marble is fixed, then it is ok to assume a constant force from the flour. I am not sure what they are trying to suggest with the crater width -- don't worry about it.
Check out this video by Bruce Yeany on Newton's 2nd and 3rd law. His YouTube channel is very good, so you might want to come back to it sometime for future experiments and demonstrations.