Question

When a knife is sharpened on a rotating grinding wheel, the fiery particles move tangent to the wheel

Answer 1

When a knife is sharpened on a rotating grinding wheel, the fiery particles move tangent to the wheel sparks are produced due to heat.

• The given phenomena represent the inertia of direction.
• The grinding wheel lets the metal bits from the knife's edge to fall out. As a result the smaller pieces get heated up and start glowing due to elevated temperatures because of the friction between the two surfaces.
• The formation of sparks lets, the force acting on them to become zero. Thus,  due to the inertia of direction, the sparks start traveling in their initial direction of the  tangent motion at the grinding wheel's rim.