Learning goal: to understand the nature of electric fields and how to draw field lines. electric field lines are a tool used to visualize electric fields. a field line is drawn beginning at a positive charge and ending at a negative charge. field lines may also appear from the edge of a picture or disappear at the edge of the picture. such lines are said to begin or end at infinity. the field lines are directed so that the electric field at any point is tangent to the field line at that point.

One hazard of space travel is debris left by previous missions. there are several thousand masses large enough to detect by radar orbiting the earth, but there are far greater numbers of very small masses such as flakes of paint. calculate the force exerted by a 0.110 mg chip of paint that strikes a space shuttle window at a relative speed of 5.00 ✕ 103 m/s and sticks, given the collision lasts 6.00 ✕ 10-8 s. such a collision chipped the window of the ill-fated challenger in june 1983, causing $50,000 of damage.