Infrared Laserdiode

The direction of frictional resisting forces is in the common tangent plane of the two surfaces, and directly opposed to their relative motion.

Infrared LaserPointer for Rifle

[Specifications] Mode: CW Wavelength: 850nm Output Power: <1500mw(choose) Operating Voltage: 12-24V Operating Current: <450mA Operating Temperature: -20°~+50° Storage Temperature: -40°~+85° Housing Material: Environmental aluminum Mean time to failure: >10000H Laser Safety: Class ⅢB Line Width:<3mm at  1m distance Divergence Angle: 110deg Lens: Glass collimator Diameter x Length: 33x33x75mm Driver circuit: ACC

A cone of second order is uniquely determined by five of its edges or by five of its tangent planes, or by four edges and the tangent plane at one of them, &c. &c.

Infrared LaserPointer Amazon

If we revolve this about the line of the radius in question, as an axis, the circle will generate the sphere again, and the tangent line will generate the tangent plane.

Considered as a curved surface, concentric with the earth, a tangent plane to such a surface is the plane of the horizon.