Introductory Physics Volume Two

6 Electric Field 1.1
θ
First draw a free body diagram for one of the masses:
θ
2
F T
F E
mg
Sum forces:
∑ ⃗F = î(FT sin θ 2 − F E) + ĵ(F T cos θ 2 − mg) = 0
This gives two equations:
F E = F T sin θ 2
F T cos θ 2 = mg
Solving for the electric force F E gives
F E = mg tan θ 2 = (.004kg)(9.8 m s
) tan(5 ◦ ) = 3.4mN
2
Demo
Moving Charges: Place an aluminum can on a table. Perviously we
showed that we had two types or charge. If we produce either of these
types of charge the can is attracted toward the charge.
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