Type the name for the lines that show, at each point, the direction of the force a field would exert.
A field drawing is a working tool: at any marked point, it hands you the direction of the force there. This lesson is the read, practiced until it is automatic.
You have all three direction conventions. The read puts them to work.
Here is the read, on Earth's field with a point P marked.
First, find the marked point and the arrow on the nearest field line.
Second, check what the arrows were drawn for. Gravitational arrows are drawn for any mass. Electric arrows are drawn for a positive test charge. Magnetic arrows are drawn for a magnet's north pole.
Third, give the direction. An object the arrows were drawn for feels the force along the arrow.
An object of the opposite kind, a negative charge or a magnet's south pole, feels the force opposite the arrow.
A 2 kilogram rock sits at P. Which way does the force on it act?
A 3 kilogram probe sits at the marked point near Mars. The nearest arrow points toward Mars. Which way does the force on the probe act?
The probe is a mass.
Gravitational arrows are drawn for any mass, so the probe matches the arrows.
A matching object feels the force along the arrow.
The force on the probe acts toward Mars, along the arrow.
A bead with positive charge sits at P. Which way does the force on it act?
A bead with positive charge sits at P. Which way does the force on it act?
A bead carrying negative charge sits at the marked point near a positively charged sphere. The nearest arrow points away from the sphere. Which way does the force on the bead act?
Electric arrows are drawn for a positive test charge.
The bead's charge is negative: the opposite kind.
An opposite-kind object feels the force opposite the arrow.
The force on the bead acts toward the sphere, against the arrow.
A bead with negative charge sits at P. Which way does the force on it act?
The drawn field is an electric field. A bead with positive charge sits at P. Which way does the force on it act?
A compass needle's north pole sits at P. Which way does the force on that pole act?
A bead carrying negative charge sits at P in the drawn field. What force, if any, acts on the bead?
A small magnet's south pole sits at P. Which way does the force on that pole act?
The drawn arrows point away from the charged sphere. Which object placed at P would feel a force back toward the sphere?