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This animation very simply demonstrates the motion of a screw relative to a meshed nut. This is important for understanding the cross product of two vectors. The cross product is written in the following way:

`bbv_3=bbv_1xxbbv_2`

where the third vector, `bbv_3` is perpendicular to the plane of the intersection of `bbv_1` with `bbv_2`. That leaves us with the question of which way of the two possible directions does `bbv_3` point? Conventional wisdom says that it points in the direction determined by the Right Hand Rule The right hand rule method is to position the right hand such that an arrow from the wrist toward the knuckles along the back of the hand is along `bbv_1` and then curl the the fingers of that hand so that they are along `bbv_2`. Then the direction of the right thumb will be in direction of the cross product `bbv_1xxbbv_2`
Because the cross product is the product
of two other vectors it is sometimes called a pseudovector of axial vector. But it does have both
direction and magnitude so it can represent physical quantities like angular momentum.

It much easier to determine the direction of cross product by noticing the direction of movement of the axis of screw with external threads that is meshed in a fixed nut with internal threads. There are two types of screw and nut threads: Clockwise and Counterclockwise or right handed and left handed. When a screw is turned clockwise into a clockwise nut thread, the screw advances into the nut. When a screw is turned clockwise in a counterclockwise nut thread, the screw recedes back out of the nut. It is that behavior of a screw into a nut that we will illustrate here.

`bbB(bbr)=(mu_0q)/(4pi)bbvxx(bbr-bbr')/|(bbr-bbr')|^3`

where `bbr'` is the location of the charge and `bbr` is the location of the field (observation) point.Note that in `xyz` coordinates the cross product can be written as a determinant:

`bbvxxbbr=|[bbhatx,bbhaty,bbhatz], [v_x,v_y,v_z], [r_x,r_y,r_z]|= (v_yr_z-v_zr_y)bbhatx-(v_xr_z-v_zr_x)bbhaty+(v_xr_y-v_yr_x)bbhatz`

The determinant expression shows how the handedness of the cross product comes into play. To simplify geometry we will set `bbv=vbbhatz` and choose `bbr=rbbhatx` which results in`bbvxxbbr=v_zr_xbbhaty`

In other words, if both `v_z` and `r_x` are both positive, then `bbvxxbbr` will be positive and along the `bbhaty` direction. Looking at a 3D coordinate system axes, if `bbhatz` is upward and `bbhatx` is outward and `bbhaty` is to the right then that is the direction of `bbB`. If we rotate `bbhatz` toward `bbhatx` then that is a counter-clockwise rotation and it would move a righthanded screw along the `+bbhaty`We need to make the crossproduct progress to the right. To show that, we need to displace all of the threads by small amounts for each animation frame.

For nomenclature of the parameters of a screw see Screw Thread Terminology We will use a subset of these names here. In order to advance along the screw axis when rotated about the axis, spirals will be displaced horizontally by the space between them. This distance is called the pitch which is called the ptich. In english units for a screw, this is the the inverse of the "threads per inch".