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Review Forces.

Review the 211 textbook, Chap 3 is on vectors. Section 9.3 covers dot product. Section 12.10 covers the cross-product. Chap 5-8 cover forces. Chap 13 is about the gravitational force. You can access all those chapter on the etext in MasteringPhysics.

A summary of the video is available here:

Unit Vectors.

A unit vector is a vector of length 1. They are used when we need to indicate the direction of a physical vector quantity without changing its magnitude.

For example the force of gravity can be written as

\vec{F}_{G} = \frac{Gm_1m_2}{r^2}\hat r

where the \hat r is a unit vector along the straight line joining the two objects.

Sometimes the unit vector will be obvious, sometimes you will need to calculate it by finding a vector you know in that direction and dividing by its length.

\hat r= \frac{\vec{r}}{r}

Let me illustrate this procedure with the force of gravity and next week we will apply this with the electric force (and later with the magnetic force).

The worksheet for this problem solving video is available here:

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