Van der Waals and electrostatic force between polystyrene spheres

[Mr.A.Gibson]

Homework Statement

Compare gravitational, electrostatic and van der Waals forces between two 100nm polystyrene spheres which are separated by a) one micrometer b) one millimetre and c) one centimetre

Homework Equations

Gravitation and electrostatic equations are standard.

The Attempt at a Solution

After looking up a reasonable density of polystyrene, the gravitational force is easy to calculate.

Surely the electrostatic force is zero, as no charge is mentioned in the question. Also surely Van der waals force is zero at this sort of distance. But I have a feeling I'm missing something any ideas?

 

[mark726]

You are correct in your calculations for the gravitational force between the two polystyrene spheres. However, you are also correct in questioning the presence of electrostatic and van der Waals forces in this scenario.

Firstly, as you mentioned, the electrostatic force would be zero as there is no mention of charge in the question. This force is dependent on the charges of the particles involved, and without any information about their charges, we cannot calculate this force.

Secondly, the van der Waals force is a weak intermolecular force that is only significant at very small distances (on the order of nanometers). At distances of one micrometer, one millimeter, and one centimeter, this force would be negligible and can be considered to be zero.

In conclusion, for two 100nm polystyrene spheres separated by distances of one micrometer, one millimeter, and one centimeter, the only significant force would be the gravitational force. I hope this helps clarify any confusion. Let me know if you have any further questions.