Which is a characteristic of a physical change?

the chemical bonds in the substance are unchanged.
the change cannot be seen.
the molecules all move at the same speed.
the substance has reacted with another substance.

An electron moves with a constant horizontal velocity of 3.0 × 106 m/s and no initial vertical velocity as it enters a deflector inside a tv tube. the electron strikes the screen after traveling 26 cm horizontally and 19 cm vertically upward with no horizontal acceleration. what is the constant vertical acceleration provided by the deflector? (the effects of gravity can be ignored.)