A student is experimenting with electric charges. The student rubs a plastic rod with a dry cloth. The plastic rod becomes positively charged. Explain why the friction between the plastic and the cloth causes the plastic to become positively charged. igcse physics

When you push downward on a book at rest on a table, you feel an upward force. does this force depend on friction? defend your answer.

If a tank filled with water contains a block and the height of the water above point a within the block is 0.8 meter, what is the pressure at point a?

In a simplified model of the human eye, the aqueous and vitreous humors and the lens all have a refractive index of 1.40, and all the refraction occurs at the cornea, whose vertex is 2.60 cm from the retina. what should be the radius of curvature of the cornea such that the image of an object 40.0 cm from the cornea’s vertex is focused on the retina?